Is an Unusual Manganese Deposit Evidence of Precambrian Aerobic Photosynthesis?

Unusual manganese enrichment in the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa

Authors:

Ossa ossa et al

Abstract:

An unusual sediment-hosted manganese deposit is described from the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa. MnO contents up to 15 wt.% were observed in marine clastic and chemical sedimentary rocks. Mn enrichment is interpreted to have resulted from the hydrothermal alteration of manganiferous shale and BIF parent rocks, the primary MnO contents of which are as high as 8.5 wt.%. A detailed mineralogical and petrographic study shows that these parent rocks are characterized by manganoan siderite, ferroan rhodochrosite and other Mn–Fe-rich mineral phases, such as kutnohorite and Fe–Mn-chlorite. Their hypogene alteration gave rise to a diversification of mineral assemblages where ferroan tephroite, calcian rhodochrosite, rhodochrosite, pyrochroite, pyrophanite, cronstedtite, manganoan Fe-rich chlorite and manganoan phlogopite partially or totally replaced the previous mineral assemblage. Thermodynamic modeling performed on chlorite phases associated with the described mineral assemblages illustrates a decrease of average crystallization temperatures from ca. 310 °C during early metamorphic stages to ca. 250 °C during a hydrothermal stage. Mineral transformation processes were thus related to retrograde metamorphism and/or hydrothermal alteration post-dating metamorphism and gave rise to progressive Mn enrichment from unaltered parent to altered rocks. The timing of hypogene alteration was constrained by 40Ar/39Ar dating to between about 1500 and 1100 Ma ago, reflecting tectonic processes associated with the Namaqua-Natal orogeny along the southern Kaapvaal Craton margin. Manganiferous shale and BIF of the Mozaan Group may represent the oldest known examples of primary sedimentary Mn deposition, related to oxidation of dissolved Mn(II) by free oxygen in a shallow marine environment. Oxygenic photosynthesis would have acted as a first-order control during Mn precipitation. This hypothesis opens a new perspective for better constraining secular evolution of sediment-hosted mineral deposits linked to oxygen levels in the atmosphere-hydrosphere system during the Archean Eon.

The Recipe for Atmospheric Oxygen on Earth

Earth scientists from Rice University, Yale University and the University of Tokyo are offering a new answer to the long-standing question of how our planet acquired its oxygenated atmosphere.

Based on a new model that draws from research in diverse fields including petrology, geodynamics, volcanology and geochemistry, the team's findings were published online this week in Nature Geoscience. They suggest that the rise of oxygen in Earth's atmosphere was an inevitable consequence of the formation of continents in the presence of life and plate tectonics.

"It's really a very simple idea, but fully understanding it requires a good bit of background about how the Earth works," said study lead author Cin-Ty Lee, professor of Earth science at Rice. "The analogy I most often use is the leaky bathtub. The level of water in a bathtub is controlled by the rate of water flowing in through the faucet and the efficiency by which water leaks out through the drain. Plants and certain types of bacteria produce oxygen as a byproduct of photosynthesis. This oxygen production is balanced by the sink: reaction of oxygen with iron and sulfur in the Earth's crust and by back-reaction with organic carbon. For example, we breathe in oxygen and exhale carbon dioxide, essentially removing oxygen from the atmosphere. In short, the story of oxygen in our atmosphere comes down to understanding the sources and sinks, but the 3-billion-year narrative of how this actually unfolded is more complex."

Lee co-authored the study with Laurence Yeung and Adrian Lenardic, both of Rice, and with Yale's Ryan McKenzie and the University of Tokyo's Yusuke Yokoyama. The authors' explanations are based on a new model that suggests how atmospheric oxygen was added to Earth's atmosphere at two key times: one about 2 billion years ago and another about 600 million years ago.

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Increased CO2 in 20th Century Atmosphere Changed Photosynthesis

Researchers at Umeå University and the Swedish University of Agricultural Sciences have discovered that increasing levels of CO2 in the atmosphere have shifted photosynthetic metabolism in plants over the 20th century. This is the first study worldwide that deduces biochemical regulation of plant metabolism from historical specimens. The findings are now published in the leading journal PNAS and will have an impact on new models of future CO2 concentration in the atmosphere.

In most plants, the uptake of CO2 through photosynthesis is reduced by a side reaction called photorespiration. The research group has now found that the CO2 increase in the atmosphere over the 20th century has shifted the balance between photosynthesis and photorespiration toward photosynthesis. This shift has so far contributed to the global vegetation's ability to dampen climate change by absorbing a third of human-caused CO2 emissions. The photorespiration pathway is known to increase with temperature, which means that temperature and CO2 effects predictably oppose one another. This implies that the CO2 -driven metabolic shift will be counteracted by future temperature increases.

Vegetation's ability to capture CO2 from the atmosphere through photosynthesis is not only a decisive factor for the global CO2 balance but also in predicting future climate change and crop productivity. By monitoring plant metabolism retrospectively using historic plant samples, this research group has quantified how much increased atmospheric CO2 levels during the 20th century have contributed to plants' ability to capture the greenhouse gas carbon dioxide.

"Until recently, studying how plants respond to increases in CO2 on decadal to centennial time scales has relied on simulations based on short-term experiments, because methods to detect long-term metabolic changes were not available. By reconstructing past metabolic shifts in response to environmental changes, we lay the foundation for better modelling of future plant performance," says Jürgen Schleucher, professor at the Department of Medical Biochemistry and Biophysics at Umeå University, who led the study.

link.

paper link.

Did the Oceans get Arsenic Poisoning at the end of the Huronian Glaciations/Siderian PaleoProterozoic Snowball Earth?

By examining rocks at the bottom of ancient oceans, an international group of researchers have revealed that arsenic concentrations in the oceans have varied greatly over time. But also that in the very early oceans, arsenic co-varied with the rise of atmospheric oxygen and coincided with the coming and going of global glaciations. The study was recently published in the Nature Group Journal, Scientific Reports.

"In the article we argue that when we first see the appearance of complex life on Earth, is when life have developed mechanisms to resist catastrophic chemical changes forced by global glaciations. And that this enabled the expansion of complex life in oceans, and paved the way for our own evolution", says Dr Ernest Chi Fru of Stockholm University, who has led the research group.

The first appearance of oxygen in the atmosphere occurred at a time when marine arsenic concentrations were dramatically low, at about after 2.45 billion years ago. This is also a period when Earth experienced its first known global glaciation. At the end of these glaciations, considerable rise in marine arsenic concentrations concurred with rapid demise of atmospheric oxygen.

The authors infer -- from the way modern photosynthetic organisms react to changing marine arsenic concentrations -- that this event was due to widespread ocean toxicity resulting from the release of toxic elements into the oceans when the ice melted.

link.

Now THAT'S Green Power: a Fuel Cell Using Cyanobacteria Respiration and Photosynthesis

Researchers from Concordia University in Montreal are looking to tap into what may be the most plentiful yet overlooked source of power in the world. The group has invented a power cell that harnesses the electricity created during the natural processes of photosynthesis and respiration in blue-green algae.

The microorganisms, also known as cyanobacteria, can be found in just about any ecosystem on the planet, across all latitudes, with respiration and photosynthesis taking place in the organism's cells both involving electron transfer chains.

"By taking advantage of a process that is constantly occurring all over the world, we've created a new and scalable technology that could lead to cheaper ways of generating carbon-free energy," says Concordia engineering professor Muthukumaran Packirisamy.

We've seen algae put to similar use in a building in Germany, and on a smaller scale in algae-powered lamps, but algae is probably better know for its potential to produce energy as a biodiesel feedstock.

The Concordia group's prototype photosynthetic power cell is currently small scale, with the algae being placed in an anode chamber, alongside the cathode and proton exchange membrane that make up the unit. An external load connected to the device extracts the electrons released by the algae to the electrode surface.

According to the paper, the team was able to measure open-circuit voltage as high as 993 millivolts, while a peak power of 175 microwatts was obtained under an external load of 850 ohms. The team claims its Micro Photosynthetic Power Cell (μPSC) could produce a power density of 36.23 microwatts/cm2, a voltage density of 80 millivolts/cm2, and a current density of 93.38 microamps/cm2 under test conditions.

link.

Did Suspension Feeding Animals in the Ediacaran Cause an Ecological Revolution in Autotrophs?

Proterozoic photosynthesis – a critical review

Author:

Butterfield

Abstract:

Chlorophyll-based photosynthesis has fuelled the biosphere since at least the early Archean, but it was the ecological takeover of oxygenic cyanobacteria in the early Palaeoproterozoic, and of photosynthetic eukaryotes in the late Neoproterozoic, that gave rise to a recognizably modern ocean–atmosphere system. The fossil record offers a unique view of photosynthesis in deep time, but is deeply compromised by differential preservation and non-diagnostic morphologies. The pervasively polyphyletic expression of modern cyanobacterial phenotypes means that few Proterozoic fossils are likely to be members of extant clades; rather than billion-year stasis, their similarity to modern counterparts is better interpreted as a combination of serial convergence and extinction, facilitated by high levels of horizontal gene transfer. There are few grounds for identifying cyanobacterial akinetes or crown-group Nostocales in the Proterozoic record. Such recognition undermines the results of various ancestral state reconstruction analyses, as well as molecular clock estimates calibrated against demonstrably problematic Proterozoic fossils. Eukaryotic organisms are likely to have acquired their (stem-group nostocalean) photoendosymbionts/plastids by at least the Palaeoproterozoic, but remained ecologically marginalized by incumbent cyanobacteria until the late Neoproterozoic appearance of suspension-feeding animals.

Engineering Synthetic Chromophores to Improve Photosynthesis Through Using "Quantum Goldilocks Effect"

Nature has had billions of years to perfect photosynthesis, which directly or indirectly supports virtually all life on Earth. In that time, the process has achieved almost 100 percent efficiency in transporting the energy of sunlight from receptors to reaction centers where it can be harnessed -- a performance vastly better than even the best solar cells.

One way plants achieve this efficiency is by making use of the exotic effects of quantum mechanics -- effects sometimes known as "quantum weirdness." These effects, which include the ability of a particle to exist in more than one place at a time, have now been used by engineers at MIT to achieve a significant efficiency boost in a light-harvesting system.

Surprisingly, the MIT researchers achieved this new approach to solar energy not with high-tech materials or microchips -- but by using genetically engineered viruses.

This achievement in coupling quantum research and genetic manipulation, described this week in the journal Nature Materials, was the work of MIT professors Angela Belcher, an expert on engineering viruses to carry out energy-related tasks, and Seth Lloyd, an expert on quantum theory and its potential applications; research associate Heechul Park; and 14 collaborators at MIT and in Italy.

Lloyd, a professor of mechanical engineering, explains that in photosynthesis, a photon hits a receptor called a chromophore, which in turn produces an exciton -- a quantum particle of energy. This exciton jumps from one chromophore to another until it reaches a reaction center, where that energy is harnessed to build the molecules that support life.

But the hopping pathway is random and inefficient unless it takes advantage of quantum effects that allow it, in effect, to take multiple pathways at once and select the best ones, behaving more like a wave than a particle.

This efficient movement of excitons has one key requirement: The chromophores have to be arranged just right, with exactly the right amount of space between them. This, Lloyd explains, is known as the "Quantum Goldilocks Effect."

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In the Future, Artificial Photosynthetic "Plants" may Produce Natural gas and Gasoline

Imagine creating artificial plants that make gasoline and natural gas using only sunlight. And imagine using those fuels to heat our homes or run our cars without adding any greenhouse gases to the atmosphere. By combining nanoscience and biology, researchers led by scientists at University of California, Berkeley, have taken a big step in that direction.

Peidong Yang, a professor of chemistry at Berkeley and co-director of the school's Kavli Energy NanoSciences Institute, leads a team that has created an artificial leaf that produces methane, the primary component of natural gas, using a combination of semiconducting nanowires and bacteria. The research, detailed in the online edition of Proceedings of the National Academy of Sciences in August, builds on a similar hybrid system, also recently devised by Yang and his colleagues, that yielded butanol, a component in gasoline, and a variety of biochemical building blocks.

The research is a major advance toward synthetic photosynthesis, a type of solar power based on the ability of plants to transform sunlight, carbon dioxide and water into sugars. Instead of sugars, however, synthetic photosynthesis seeks to produce liquid fuels that can be stored for months or years and distributed through existing energy infrastructure.

In a roundtable discussion on his recent breakthroughs and the future of synthetic photosynthesis, Yang said his hybrid inorganic/biological systems give researchers new tools to study photosynthesis -- and learn its secrets.

link.

Improving Photosynthesis Through Biotech for Food and Bio Fuels

Redesigning photosynthesis to sustainably meet global food and bioenergy demand

Authors:

Ort et al

Abstract:

The world’s crop productivity is stagnating whereas population growth, rising affluence, and mandates for biofuels put increasing demands on agriculture. Meanwhile, demand for increasing cropland competes with equally crucial global sustainability and environmental protection needs. Addressing this looming agricultural crisis will be one of our greatest scientific challenges in the coming decades, and success will require substantial improvements at many levels. We assert that increasing the efficiency and productivity of photosynthesis in crop plants will be essential if this grand challenge is to be met. Here, we explore an array of prospective redesigns of plant systems at various scales, all aimed at increasing crop yields through improved photosynthetic efficiency and performance. Prospects range from straightforward alterations, already supported by preliminary evidence of feasibility, to substantial redesigns that are currently only conceptual, but that may be enabled by new developments in synthetic biology. Although some proposed redesigns are certain to face obstacles that will require alternate routes, the efforts should lead to new discoveries and technical advances with important impacts on the global problem of crop productivity and bioenergy production.

Was There an Oxygen Spike, Crash and Mass Extinction During the PaleoArchean?

Variations in the abundance of photosynthetic oxygen through Precambrian and Paleozoic time in relation to biotic evolution and mass extinctions: evidence from Mn/Fe ratios

Author:

Jackson

Abstract:

This paper reports new information about variations in the abundance of photosynthetic oxygen through Precambrian and Paleozoic time. Non-detrital marine sediments (cherts, limestones, and dolomite) were analysed for NH2OH·HCl/acetic acid-extractable Mn and Fe, and the Mn/Fe ratio (a proxy for the oxidation–reduction potential of the sediment at the time of deposition) was plotted against geologic age. The method has never before been applied to ancient sediments, but previously published data produced independently by other methods confirmed its applicability and underlying assumptions. The Mn/Fe ratio was unexpectedly high ca. 3.416 Ga, implying localised oxidation due to oxygen production by cyanobacteria, but fell dramatically over the interval 3.416–3.298 Ga, suggesting mass mortality or mass extinction of early Archaean cyanobacteria owing to asteroid impacts. However, the ratio increased continuously, though at episodically varying rates, from a minimum at ∼1.8783 Ga to a maximum at ∼0.680 Ga, signifying accumulation of oxygen in the atmosphere and hydrosphere. The rate of increase was relatively high at first but dropped abruptly at some point during the interval 1.8783–1.6 Ga, possibly signalling the appearance of eukaryotic herbivores. The ratio increased exponentially from 1.6 to 0.8 Ga and then rose more rapidly from 0.8 to 0.680 Ga, indicating a late Proterozoic upsurge of oxygen production, whereupon it fell catastrophically to a minimum in the Cambrian, reflecting widespread anoxia due to mass extinction of Ediacaran organisms. The crisis at the Precambrian–Cambrian boundary was followed by a logarithmic increase from the Cambrian to the Permian, indicating a resurgence of photosynthetic activity.

Trace Hydrocarbons in Archean Rocks are NOT Reliable Biomarkers

Reappraisal of hydrocarbon biomarkers in Archean rocks

Authors:

French et al

Abstract:

Hopanes and steranes found in Archean rocks have been presented as key evidence supporting the early rise of oxygenic photosynthesis and eukaryotes, but the syngeneity of these hydrocarbon biomarkers is controversial. To resolve this debate, we performed a multilaboratory study of new cores from the Pilbara Craton, Australia, that were drilled and sampled using unprecedented hydrocarbon-clean protocols. Hopanes and steranes in rock extracts and hydropyrolysates from these new cores were typically at or below our femtogram detection limit, but when they were detectable, they had total hopane (less than 37.9 pg per gram of rock) and total sterane (less than 32.9 pg per gram of rock) concentrations comparable to those measured in blanks and negative control samples. In contrast, hopanes and steranes measured in the exteriors of conventionally drilled and curated rocks of stratigraphic equivalence reach concentrations of 389.5 pg per gram of rock and 1,039 pg per gram of rock, respectively. Polycyclic aromatic hydrocarbons and diamondoids, which exceed blank concentrations, exhibit individual concentrations up to 80 ng per gram of rock in rock extracts and up to 1,000 ng per gram of rock in hydropyrolysates from the ultraclean cores. These results demonstrate that previously studied Archean samples host mixtures of biomarker contaminants and indigenous overmature hydrocarbons. Therefore, existing lipid biomarker evidence cannot be invoked to support the emergence of oxygenic photosynthesis and eukaryotes by ∼2.7 billion years ago. Although suitable Proterozoic rocks exist, no currently known Archean strata lie within the appropriate thermal maturity window for syngenetic hydrocarbon biomarker preservation, so future exploration for Archean biomarkers should screen for rocks with milder thermal histories.

Carbonaceous Compression Fossils of Macroscopic Benthic Phototrophs Found From Marinoan Cryogenian NeoProterozoic South China

The survival of benthic macroscopic phototrophs on a Neoproterozoic snowball Earth

Authors:

Ye et al

Abstract:

The greatest ice ages in Earth's history occurred during the 654–635 Ma Marinoan glaciation, when glaciers reached tropical oceans and our planet approached a snowball Earth condition. Paleontological and genomic data suggest that several eukaryotic groups must have survived the Marinoan glaciation. But their fossil record is scarce and limited to microbes, whose ecological and physiological ranges are poorly constrained, thus hampering a full understanding of how and where eukaryotic life—particularly macroscopic phototrophs—survived this snowball Earth. Here we report carbonaceous compression fossils from the Marinoan-age Nantuo Formation in South China. These fossils are preserved in thin black shales sandwiched between glacial diamictites deposited in inner shelf environments of the mid-latitudinal Yangtze block. Some of these fossils are interpreted as benthic macroalgae. Thus, the Marinoan glaciation must have been punctuated by episodes of open waters where habitable benthic substrates were available in the photic zone and along the coast of mid-latitudinal continents. Such open waters may have been the refugia where macroscopic phototrophs survived the Marinoan glaciation and subsequently diversified in the early Ediacaran Period.

Evidence of Pre Great Oxidation Event Aerobic Photosynthesis

Selenium isotopes support free O2 in the latest Archean

Authors:

Stüeken et al

Abstract:

Selenium (Se) undergoes redox transformations and isotopic fractionations at relatively high redox potentials and could therefore provide insight into changes in oceanic and atmospheric O2 levels over Earth's history. We test this idea with Se data from the 2.5 Ga Mount McRae Shale (Hamersley Basin, Australia), which records temporary enrichments in abundances and isotopes of other redox-sensitive elements indicating a "whiff of oxygen" in Earth's atmosphere before the Great Oxidation Event. Se isotopic ratios expressed as δ82/78Se and abundances relative to crustal background show significant positive excursions of up to 1.1‰ and an enrichment 13 times above background, respectively, overlapping with excursions in Mo and N isotopes and abundances. Because Se has a relatively high redox potential and photosynthetic oxidation pathways are unknown, our data thus suggest that Se was mobilized by free O2 during this interval. The isotopic fractionation likely occurred during transport of Se oxyanions from the site of weathering to the outer shelf. Although O2 could have been produced locally on land and may not necessarily have increased in the global atmosphere, our results strengthen the inference of an early origin of oxygenic photosynthesis long before the Paleoproterozoic Great Oxidation Event. This is the first report of a Se isotope excursion in the Precambrian rock record, and it confirms that Se isotopes can serve as a useful redox proxy in deep time.

Elysia chlorotica: Meet the Photosynthetic Sea Slug

How a brilliant-green sea slug manages to live for months at a time "feeding" on sunlight, like a plant, is clarified in a recent study published in The Biological Bulletin.

The authors present the first direct evidence that the emerald green sea slug's chromosomes have some genes that come from the algae it eats.

These genes help sustain photosynthetic processes inside the slug that provide it with all the food it needs.

Importantly, this is one of the only known examples of functional gene transfer from one multicellular species to another, which is the goal of gene therapy to correct genetically based diseases in humans.

"Is a sea slug a good [biological model] for a human therapy? Probably not. But figuring out the mechanism of this naturally occurring gene transfer could be extremely instructive for future medical applications," says study co-author Sidney K. Pierce, an emeritus professor at University of South Florida and at University of Maryland, College Park.

The team used an advanced imaging technique to confirm that a gene from the alga V. litorea is present on the E. chlorotica slug's chromosome. This gene makes an enzyme that is critical to the function of photosynthetic "machines" called chloroplasts, which are typically found in plants and algae.

It has been known since the 1970s that E. chloritica "steals" chloroplasts from V. litorea (called "kleptoplasty") and embeds them into its own digestive cells. Once inside the slug cells, the chloroplasts continue to photosynthesize for up to nine months--much longer than they would perform in the algae. The photosynthesis process produces carbohydrates and lipids, which nourish the slug.

How the slug manages to maintain these photosynthesizing organelles for so long has been the topic of intensive study and a good deal of controversy. "This paper confirms that one of several algal genes needed to repair damage to chloroplasts, and keep them functioning, is present on the slug chromosome," Pierce says. "The gene is incorporated into the slug chromosome and transmitted to the next generation of slugs." While the next generation must take up chloroplasts anew from algae, the genes to maintain the chloroplasts are already present in the slug genome, Pierce says.

link.

Scientists Successfully 'Hack' Rubisco, "Improve" Photosynthesis

It is difficult to find fault with a process that can create food from sunlight, water and air, but for many plants, there is room for improvement. Researchers have taken an important step towards enhancing photosynthesis by engineering plants with enzymes from blue-green algae that speed up the process of converting carbon dioxide into sugars.

The results, published today in Nature, surmount a daunting hurdle on the path to boosting plant yields — a goal that is taking on increasing importance as the world’s population grows.

“With the limited ability to increase land use for agriculture, there’s a huge interest in trying to improve yield across all the major crops,” says Steven Gutteridge, a research fellow at chemical firm DuPont’s crop-protection division in Newark, Delaware.

Researchers have long wanted to increase yields by targeting Rubisco, the enzyme responsible for converting carbon dioxide into sugar. Rubisco is possibly the most abundant protein on Earth, and can account for up to half of all the soluble protein found in a leaf.

But one reason for its abundance is its inefficiency: plants produce so much Rubisco in part to compensate for its slow catalysis. Some have estimated that tinkering with Rubisco and ways to boost the concentration of carbon dioxide around it could generate up to a 60% increase in the yields of crops such as rice and wheat.

link.

The First Synthetic Leaf

The "first man-made biological leaf" could enable humans to colonise space from Dezeen on Vimeo.

hmm.  I wonder how the chloroplasts can be sustained outside the plant cell...

Understanding Oxygen's Rise in the PaleoAtmosphere

The rise of oxygen in Earth’s early ocean and atmosphere

Authors:

Lyons et al

Abstract:

The rapid increase of carbon dioxide concentration in Earth’s modern atmosphere is a matter of major concern. But for the atmosphere of roughly two-and-half billion years ago, interest centres on a different gas: free oxygen (O2) spawned by early biological production. The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in Earth’s history.

Paleosols Indicate Atmospheric Oxygen During MesoArchean Archean, 700 Million Years Earlier

Oxygen appeared in the atmosphere up to 700 million years earlier than we previously thought, according to research published today in the journal Nature, raising new questions about the evolution of early life.

Researchers from the University of Copenhagen and University of British Columbia examined the chemical composition of three-billion-year-old soils from South Africa – the oldest soils on Earth – and found evidence for low concentrations of atmospheric oxygen. Previous research indicated that oxygen began accumulating in the atmosphere only about 2.3 billion years ago during a dynamic period in Earth's history referred to as the Great Oxygenation Event.

"We've always known that oxygen production by photosynthesis led to the eventual oxygenation of the atmosphere and the evolution of aerobic life," says Sean Crowe, co-lead author of the study and an assistant professor in the Departments of Microbiology and Immunology, and Earth, Ocean and Atmospheric Sciences at UBC.

"This study now suggests that the process began very early in Earth's history, supporting a much greater antiquity for oxygen producing photosynthesis and aerobic life," says Crowe, who conducted the research while a post-doctoral fellow at Nordic Center for Earth Evolution at the University of Southern Denmark in partnership with the centre's director Donald Canfield.

link.

paper link.

Manganese Based Photosynthesis Siderian PaleoProterozoic Detected?

For most terrestrial life on Earth, oxygen is necessary for survival. But the planet's atmosphere did not always contain this life-sustaining substance, and one of science's greatest mysteries is how and when oxygenic photosynthesis—the process responsible for producing oxygen on Earth through the splitting of water molecules—first began. Now, a team led by geobiologists at the California Institute of Technology (Caltech) has found evidence of a precursor photosystem involving manganese that predates cyanobacteria, the first group of organisms to release oxygen into the environment via photosynthesis.

The findings, outlined in the June 24 early edition of the Proceedings of the National Academy of Sciences (PNAS), strongly support the idea that manganese oxidation—which, despite the name, is a chemical reaction that does not have to involve oxygen—provided an evolutionary stepping-stone for the development of water-oxidizing photosynthesis in cyanobacteria.

"Water-oxidizing or water-splitting photosynthesis was invented by cyanobacteria approximately 2.4 billion years ago and then borrowed by other groups of organisms thereafter," explains Woodward Fischer, assistant professor of geobiology at Caltech and a coauthor of the study. "Algae borrowed this photosynthetic system from cyanobacteria, and plants are just a group of algae that took photosynthesis on land, so we think with this finding we're looking at the inception of the molecular machinery that would give rise to oxygen."

Photosynthesis is the process by which energy from the sun is used by plants and other organisms to split water and carbon dioxide molecules to make carbohydrates and oxygen. Manganese is required for water splitting to work, so when scientists began to wonder what evolutionary steps may have led up to an oxygenated atmosphere on Earth, they started to look for evidence of manganese-oxidizing photosynthesis prior to cyanobacteria. Since oxidation simply involves the transfer of electrons to increase the charge on an atom—and this can be accomplished using light or O2—it could have occurred before the rise of oxygen on this planet.

"Manganese plays an essential role in modern biological water splitting as a necessary catalyst in the process, so manganese-oxidizing photosynthesis makes sense as a potential transitional photosystem," says Jena Johnson, a graduate student in Fischer's laboratory at Caltech and lead author of the study.

To test the hypothesis that manganese-based photosynthesis occurred prior to the evolution of oxygenic cyanobacteria, the researchers examined drill cores (newly obtained by the Agouron Institute) from 2.415 billion-year-old South African marine sedimentary rocks with large deposits of manganese.

Manganese is soluble in seawater. Indeed, if there are no strong oxidants around to accept electrons from the manganese, it will remain aqueous, Fischer explains, but the second it is oxidized, or loses electrons, manganese precipitates, forming a solid that can become concentrated within seafloor sediments.

"Just the observation of these large enrichments—16 percent manganese in some samples—provided a strong implication that the manganese had been oxidized, but this required confirmation," he says.

To prove that the manganese was originally part of the South African rock and not deposited there later by hydrothermal fluids or some other phenomena, Johnson and colleagues developed and employed techniques that allowed the team to assess the abundance and oxidation state of manganese-bearing minerals at a very tiny scale of 2 microns.

"And it's warranted—these rocks are complicated at a micron scale!" Fischer says. "And yet, the rocks occupy hundreds of meters of stratigraphy across hundreds of square kilometers of ocean basin, so you need to be able to work between many scales—very detailed ones, but also across the whole deposit to understand the ancient environmental processes at work."

Using these multiscale approaches, Johnson and colleagues demonstrated that the manganese was original to the rocks and first deposited in sediments as manganese oxides, and that manganese oxidation occurred over a broad swath of the ancient marine basin during the entire timescale captured by the drill cores.

"It's really amazing to be able to use X-ray techniques to look back into the rock record and use the chemical observations on the microscale to shed light on some of the fundamental processes and mechanisms that occurred billions of years ago," says Samuel Webb, coauthor on the paper and beam line scientist at the SLAC National Accelerator Laboratory at Stanford University, where many of the study's experiments took place. "Questions regarding the evolution of the photosynthetic pathway and the subsequent rise of oxygen in the atmosphere are critical for understanding not only the history of our own planet, but also the basics of how biology has perfected the process of photosynthesis."

Once the team confirmed that the manganese had been deposited as an oxide phase when the rock was first forming, they checked to see if these manganese oxides were actually formed before water-splitting photosynthesis or if they formed after as a result of reactions with oxygen. They used two different techniques to check whether oxygen was present. It was not—proving that water-splitting photosynthesis had not yet evolved at that point in time. The manganese in the deposits had indeed been oxidized and deposited before the appearance of water-splitting cyanobacteria. This implies, the researchers say, that manganese-oxidizing photosynthesis was a stepping-stone for oxygen-producing, water-splitting photosynthesis.

"I think that there will be a number of additional experiments that people will now attempt to try and reverse engineer a manganese photosynthetic photosystem or cell," Fischer says. "Once you know that this happened, it all of a sudden gives you reason to take more seriously an experimental program aimed at asking, 'Can we make a photosystem that's able to oxidize manganese but doesn't then go on to split water? How does it behave, and what is its chemistry?' Even though we know what modern water splitting is and what it looks like, we still don't know exactly how it works. There is a still a major discovery to be made to find out exactly how the catalysis works, and now knowing where this machinery comes from may open new perspectives into its function—an understanding that could help target technologies for energy production from artificial photosynthesis. "

Next up in Fischer's lab, Johnson plans to work with others to try and mutate a cyanobacteria to "go backwards" and perform manganese-oxidizing photosynthesis. The team also plans to investigate a set of rocks from western Australia that are similar in age to the samples used in the current study and may also contain beds of manganese. If their current study results are truly an indication of manganese-oxidizing photosynthesis, they say, there should be evidence of the same processes in other parts of the world.

Do Aphids Photosynethesize?

The biology of aphids is bizarre: they can be born pregnant and males sometimes lack mouths, causing them to die not long after mating. In an addition to their list of anomalies, work published this week indicates that they may also capture sunlight and use the energy for metabolic purposes.

Aphids are unique among animals in their ability to synthesize pigments called carotenoids. Many creatures rely on these pigments for a variety of functions, such as maintaining a healthy immune system and making certain vitamins, but all other animals must obtain them through their diet. Entomologist Alain Robichon at the Sophia Agrobiotech Institute in Sophia Antipolis, France, and his colleagues suggest that, in aphids, these pigments can absorb energy from the Sun and transfer it to the cellular machinery involved in energy production.

Pop sci write up.

Paper:

Light- induced electron transfer and ATP synthesis in a carotene synthesizing insect

Authors:

1. Jean Christophe Valmalette (a)
2. Aviv Dombrovsky (b,d)
3. Pierre Brat (c)
4. Christian Mertz (c)
5. Maria Capovilla (d)
6. Alain Robichon (d)

Affiliations:

a. IM2NP UMR 7334 CNRS, Université du Sud Toulon Var, P.O. Box 20132, 83957 La Garde CEDEX, France

b. Volcani Center, Institute of Plant Protection, P.O. Box 6, 50250 Bet Dagan, Israel

c. CIRAD UMR QualiSud, 73 rue J.F. Breton, TA B-95/16, 34398 Montpellier CEDEX 5, France

d. UMR7254 INRA/CNRS/UNS, Institut Sophia Agrobiotech, 400 route des Chappes, P. O. Box 167, 06903 Sophia Antipolis, France

Abstract:

A singular adaptive phenotype of a parthenogenetic insect species (Acyrthosiphon pisum) was selected in cold conditions and is characterized by a remarkable apparition of a greenish colour. The aphid pigments involve carotenoid genes well defined in chloroplasts and cyanobacteria and amazingly present in the aphid genome, likely by lateral transfer during evolution. The abundant carotenoid synthesis in aphids suggests strongly that a major and unknown physiological role is related to these compounds beyond their canonical anti-oxidant properties. We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules. The redox potentials of molecules involved in this process would be compatible with the reduction of the NAD+ coenzyme. This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules.

hmmmm.