Spatiotemporal Characteristics Determining the Multifaceted Nature of Reactive Oxygen, Nitrogen, and Sulfur Species in Relation to Proton Homeostasis

Significance: Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) act as signaling molecules, regulating gene expression, enzyme activity, and physiological responses. However, excessive amounts of these molecular species can lead to deleterious effects, causing cellular damage and death. This dual nature of ROS, RNS, and RSS presents an intriguing conundrum that calls for a new paradigm. Recent Advances: Recent advancements in the study of photosynthesis have offered significant insights at the molecular level and with high temporal resolution into how the photosystem II oxygen-evolving complex manages to prevent harmful ROS production during the water-splitting process. These findings suggest that a dynamic spatiotemporal arrangement of redox reactions, coupled with strict regulation of proton transfer, is crucial for minimizing unnecessary ROS formation. Critical Issues: To better understand the multifaceted nature of these reactive molecular species in biology, it is worth considering a more holistic view that combines ecological and evolutionary perspectives on ROS, RNS, and RSS. By integrating spatiotemporal perspectives into global, cellular, and biochemical events, we discuss local pH or proton availability as a critical determinant associated with the generation and action of ROS, RNS, and RSS in biological systems. Future Directions: The concept of localized proton availability will not only help explain the multifaceted nature of these ubiquitous simple molecules in diverse systems but also provide a basis for new therapeutic strategies to manage and manipulate these reactive species in neural disorders, pathogenic diseases, and antiaging efforts.

Biogeochemical transformations after the emergence of oxygenic photosynthesis and conditions for the first rise of atmospheric oxygen

The advent of oxygenic photosynthesis represents the most prominent biological innovation in the evolutionary history of the Earth. The exact timing of the evolution of oxygenic photoautotrophic bacteria remains elusive, yet these bacteria profoundly altered the redox state of the ocean-atmosphere-biosphere system, ultimately causing the first major rise in atmospheric oxygen (O2 )-the so-called Great Oxidation Event (GOE)-during the Paleoproterozoic (~2.5-2.2 Ga). However, it remains unclear how the coupled atmosphere-marine biosphere system behaved after the emergence of oxygenic photoautotrophs (OP), affected global biogeochemical cycles, and led to the GOE. Here, we employ a coupled atmospheric photochemistry and marine microbial ecosystem model to comprehensively explore the intimate links between the atmosphere and marine biosphere driven by the expansion of OP, and the biogeochemical conditions of the GOE. When the primary productivity of OP sufficiently increases in the ocean, OP suppresses the activity of the anaerobic microbial ecosystem by reducing the availability of electron donors (H2 and CO) in the biosphere and causes climate cooling by reducing the level of atmospheric methane (CH4 ). This can be attributed to the supply of OH radicals from biogenic O2 , which is a primary sink of biogenic CH4 and electron donors in the atmosphere. Our typical result also demonstrates that the GOE is triggered when the net primary production of OP exceeds >~5% of the present oceanic value. A globally frozen snowball Earth event could be triggered if the atmospheric CO2 level was sufficiently small (<~40 present atmospheric level; PAL) because the concentration of CH4 in the atmosphere would decrease faster than the climate mitigation by the carbonate-silicate geochemical cycle. These results support a prolonged anoxic atmosphere after the emergence of OP during the Archean and the occurrence of the GOE and snowball Earth event during the Paleoproterozoic.

Growth and Photosynthetic Efficiency of Microalgae and Plants with Different Levels of Complexity Exposed to a Simulated M-Dwarf Starlight

Oxygenic photosynthetic organisms (OPOs) are primary producers on Earth and generate surface and atmospheric biosignatures, making them ideal targets to search for life from remote on Earth-like exoplanets orbiting stars different from the Sun, such as M-dwarfs. These stars emit very low light in the visible and most light in the far-red, an issue for OPOs, which mostly utilize visible light to photosynthesize and grow. After successfully testing procaryotic OPOs (cyanobacteria) under a simulated M-dwarf star spectrum (M7, 365-850 nm) generated through a custom-made lamp, we tested several eukaryotic OPOs: microalgae (Dixoniella giordanoi, Microchloropsis gaditana, Chromera velia, Chlorella vulgaris), a non-vascular plant (Physcomitrium patens), and a vascular plant (Arabidopsis thaliana). We assessed their growth and photosynthetic efficiency under three light conditions: M7, solar (SOL) simulated spectra, and far-red light (FR). Microalgae grew similarly in SOL and M7, while the moss P. patens showed slower growth in M7 with respect to SOL. A. thaliana grew similarly in SOL and M7, showing traits typical of shade-avoidance syndrome. Overall, the synergistic effect of visible and far-red light, also known as the Emerson enhancing effect, could explain the growth in M7 for all organisms. These results lead to reconsidering the possibility and capability of the growth of OPOs and are promising for finding biosignatures on exoplanets orbiting the habitable zone of distant stars.

Oxygenic photosynthetic responses of cyanobacteria exposed under an M-dwarf starlight simulator: Implications for exoplanet's habitability

INTRODUCTION

The search for life on distant exoplanets is expected to rely on atmospheric biosignatures detection, such as oxygen of biological origin. However, it is not demonstrated how much oxygenic photosynthesis, which on Earth depends on visible light, could work under spectral conditions simulating exoplanets orbiting the Habitable Zone of M-dwarf stars, which have low light emission in the visible and high light emission in the far-red/near-infrared. By utilizing cyanobacteria, the first organisms to evolve oxygenic photosynthesis on our planet, and a starlight simulator capable of accurately reproducing the emission spectrum of an M-dwarf in the range 350-900 nm, we could answer this question.

METHODS

We performed experiments with the cyanobacterium Chlorogloeopsis fritschii PCC6912, capable of Far-Red Light Photoacclimation (FaRLiP), which allows the strain to harvest far-red in addition to visible light for photosynthesis, and Synechocystis sp. PCC6803, a species unable to perform this photoacclimation, comparing their responses when exposed to three simulated light spectra: M-dwarf, solar and far-red. We analysed growth and photosynthetic acclimation features in terms of pigment composition and photosystems organization. Finally, we determined the oxygen production of the strains directly exposed to the different spectra.

RESULTS

Both cyanobacteria were shown to grow and photosynthesize similarly under M-dwarf and solar light conditions: Synechocystis sp. by utilizing the few photons in the visible, C. fritschii by harvesting both visible and far-red light, activating the FaRLiP response.

DISCUSSION

Our results experimentally show that an M-dwarf light spectrum could support a biological oxygen production similar to that in solar light at the tested light intensities, suggesting the possibility to discover such atmospheric biosignatures on those exoplanets if other boundary conditions are met.

Application of Spectroscopic Methods for the Identification of Superoxide Dismutases in Cyanobacteria

Superoxide dismutases (SODs) belong to the group of metalloenzymes that remove superoxide anion radicals and they have been identified in three domains of life: Bacteria, Archaea and Eucarya. SODs in Synechocystis sp. PCC 6803, Gloeobacter violaceus CCALA 979, and Geitlerinema sp. ZHR1A were investigated. We hypothesized that iron (FeSOD) and/or manganese (MnSOD) dominate as active forms in these cyanobacteria. Activity staining and three different spectroscopic methods of SOD activity bands excised from the gels were used to identify a suitable metal in the separated samples. FeSODs or enzymes belonging to the Fe-MnSOD superfamily were detected. The spectroscopic analyses showed that only Fe is present in the SOD activity bands. We found FeSOD in Synechocystis sp. PCC 6803 while two forms in G. violaceus and Geitlerinema sp. ZHR1A: FeSOD1 and FeSOD2 were present. However, no active Cu/ZnSODs were identified in G. violaceus and Geitlerinema sp. ZHR1A. We have shown that selected spectroscopic techniques can be complementary to the commonly used method of staining for SOD activity in a gel. Furthermore, the occurrence of active SODs in the cyanobacteria studied is also discussed in the context of SOD evolution in oxyphotrophs.

Advances in the Understanding of the Lifecycle of Photosystem II

Photosystem II is a light-driven water-plastoquinone oxidoreductase present in cyanobacteria, algae and plants. It produces molecular oxygen and protons to drive ATP synthesis, fueling life on Earth. As a multi-subunit membrane-protein-pigment complex, Photosystem II undergoes a dynamic cycle of synthesis, damage, and repair known as the Photosystem II lifecycle, to maintain a high level of photosynthetic activity at the cellular level. Cyanobacteria, oxygenic photosynthetic bacteria, are frequently used as model organisms to study oxygenic photosynthetic processes due to their ease of growth and genetic manipulation. The cyanobacterial PSII structure and function have been well-characterized, but its lifecycle is under active investigation. In this review, advances in studying the lifecycle of Photosystem II in cyanobacteria will be discussed, with a particular emphasis on new structural findings enabled by cryo-electron microscopy. These structural findings complement a rich and growing body of biochemical and molecular biology research into Photosystem II assembly and repair.

Complete Genome Sequencing of a Novel Gloeobacter Species from a Waterfall Cave in Mexico

Only two complete genomes of the cyanobacterial genus Gloeobacter from two very different regions of the world currently exist. Here, we present the complete genome sequence of a third member of the genus isolated from a waterfall cave in Mexico. Analysis of the average nucleotide identities (ANIs) between published Gloeobacter genomes revealed that the complete genome of this new member is only 92.7% similar to Gloeobacter violaceus and therefore we determined it to be a new species. We propose to name this new species Gloeobacter morelensis after the location in Mexico where it was isolated. The complete genome consists of one circular chromosome (4,921,229 bp), one linear plasmid (172,328 bp), and one circular plasmid (8,839 bp). Its genome is the largest of all completely sequenced genomes of Gloeobacter species. Pangenomic comparisons revealed that G. morelensis encodes 759 genes not shared with other Gloeobacter species. Despite being more closely related to G. violaceus, it features an extremely divergent psbA gene encoding an atypical D1 core subunit of Photosystem II previously only found within the genome of Gloeobacter kilaueensis. In addition, we detected evidence of concerted evolution of psbA genes encoding identical D1 in all three Gloeobacter genomes, a characteristic that seems widespread in cyanobacteria and may therefore be traced back to their last common ancestor.

Diversity and origin of carotenoid biosynthesis: its history of coevolution towards plant photosynthesis

The development of photosynthesis was a highlight in the progression of bacteria. In addition to the photosystems with their structural proteins, the photosynthesis apparatus consists of different cofactors including essential carotenoids. Thus, the evolution of the carotenoid pathways in relation to the functionality of the resulting structures in photosynthesis is the focus of this review. Analysis of carotenoid pathway genes indicates early evolutionary roots in prokaryotes. The pathway complexity leading to a multitude of structures is a result of gene acquisition, including their functional modifications, emergence of novel genes and gene exchange between species. Along with the progression of photosynthesis, carotenoid pathways coevolved with photosynthesis according to their advancing functionality. Cyanobacteria, with their oxygenic photosynthesis, became a landmark for evolutionary events including carotenogenesis. Concurrent with endosymbiosis, the cyanobacterial carotenoid pathways were inherited into algal plastids. In the lineage leading to Chlorophyta and plants, carotenoids evolved to their prominent role in protection and regulation of light energy input as constituents of a highly efficient light-harvesting complex.

Cyanobacteria and biogeochemical cycles through Earth history

Cyanobacteria are the only prokaryotes to have evolved oxygenic photosynthesis, transforming the biology and chemistry of our planet. Genomic and evolutionary studies have revolutionized our understanding of early oxygenic phototrophs, complementing and dramatically extending inferences from the geologic record. Molecular clock estimates point to a Paleoarchean origin (3.6-3.2 billion years ago, bya) of the core proteins of Photosystem II (PSII) involved in oxygenic photosynthesis and a Mesoarchean origin (3.2-2.8 bya) for the last common ancestor of modern cyanobacteria. Nonetheless, most extant cyanobacteria diversified after the Great Oxidation Event (GOE), an environmental watershed ca. 2.45 bya made possible by oxygenic photosynthesis. Throughout their evolutionary history, cyanobacteria have played a key role in the global carbon cycle.

Are plastocyanin and ferredoxin specific electron carriers or generic redox capacitors? Classical and murburn perspectives on two photosynthetic proteins

In the light reaction of oxygenic photosynthesis, plastocyanin (PC) and ferredoxins (Fd) are small/diffusible redox-active proteins playing key roles in electron transfer/transport phenomena. In the Z-scheme mechanistic purview, they are considered as specific affinity binding-based electron-relay agents, linking the functions of Cytochrome b₆f (Cyt. b₆f), Photosystem I (PS I) and Fd:NADPH oxidoreductase (FNR). The murburn explanation for photolytic photophosphorylation deems PC/Fd as generic 'redox capacitors', temporally accepting and releasing one-electron equivalents in reaction milieu. Herein, we explore the two theories with respect to structural, distributional and functional aspects of PC/Fd. Amino acid residues located on the surface loci of key patches of PC/Fd vary in electrostatic/contour (topography) signatures. Crystal structures of four different complexes each of Cyt.f-PC and Fd-FNR show little conservation in the contact-surfaces, thereby discrediting 'affinity binding-based electron transfers (ET)' as an evolutionary logic. Further, thermodynamic and kinetic data of wildtype and mutant proteins interactions do not align with Z-scheme. Furthermore, micromolar physiological concentrations of PC and the non-conducive architecture of chloroplasts render the classical model untenable. In the murburn model, as PC is optional, the observation that plants lacking PC survive and grow is justified. Further, the low physiological concentration/distribution of PC in chloroplast lumen/stroma is supported by murburn equilibriums, as higher concentrations would limit electron transfers. Thus, structural evidence, interactive dynamics with redox partners and physiological distribution/role of PC/Fd support the murburn perspective that these proteins serve as generic redox-capacitors in chloroplasts.Communicated by Ramaswamy H. Sarma.

What's in a name? The case of cyanobacteria

A redefinition of the cyanobacterial lineage has been proposed based on phylogenomic analysis of distantly related nonphototrophic lineages. We define Cyanobacteria here as "Organisms in the domain bacteria able to carry out oxygenic photosynthesis with water as an electron donor and to reduce carbon dioxide as a source of carbon, or those secondarily evolved from such organisms."

On the origin of oxygenic photosynthesis and Cyanobacteria

Oxygenic phototrophs have played a fundamental role in Earth's history by enabling the rise of atmospheric oxygen (O₂ ) and paving the way for animal evolution. Understanding the origins of oxygenic photosynthesis and Cyanobacteria is key when piecing together the events around Earth's oxygenation. It is likely that photosynthesis evolved within bacterial lineages that are not extant, so it can be challenging when studying the early history of photosynthesis. Recent genomic and molecular evolution studies have transformed our understanding about the evolution of photosynthetic reaction centres and the evolution of Cyanobacteria. The evidence reviewed here highlights some of the most recent advances on the origin of photosynthesis both at the genomic and gene family levels.

Limited oxygen production in the Mesoarchean ocean

The Archean Eon was a time of predominantly anoxic Earth surface conditions, where anaerobic processes controlled bioessential element cycles. In contrast to "oxygen oases" well documented for the Neoarchean [2.8 to 2.5 billion years ago (Ga)], the magnitude, spatial extent, and underlying causes of possible Mesoarchean (3.2 to 2.8 Ga) surface-ocean oxygenation remain controversial. Here, we report δ¹⁵N and δ¹³C values coupled with local seawater redox data for Mesoarchean shales of the Mozaan Group (Pongola Supergroup, South Africa) that were deposited during an episode of enhanced Mn (oxyhydr)oxide precipitation between ∼2.95 and 2.85 Ga. Iron and Mn redox systematics are consistent with an oxygen oasis in the Mesoarchean anoxic ocean, but δ¹⁵N data indicate a Mo-based diazotrophic biosphere with no compelling evidence for a significant aerobic nitrogen cycle. We propose that in contrast to the Neoarchean, dissolved O₂ levels were either too low or too limited in extent to develop a large and stable nitrate reservoir in the Mesoarchean ocean. Since biological N₂ fixation was evidently active in this environment, the growth and proliferation of O₂-producing organisms were likely suppressed by nutrients other than nitrogen (e.g., phosphorus), which would have limited the expansion of oxygenated conditions during the Mesoarchean.

Formation of stromatolite lamina at the interface of oxygenic-anoxygenic photosynthesis

In modern stromatolites, mineralization results from a complex interplay between microbial metabolisms, the organic matrix, and environmental parameters. Here, we combined biogeochemical, mineralogical, and microscopic analyses with measurements of metabolic activity to characterize the mineralization processes and products in an emergent (<18 months) hypersaline microbial mat. While the nucleation of Mg silicates is ubiquitous in the mat, the initial formation of a Ca-Mg carbonate lamina depends on (i) the creation of a high-pH interface combined with a major change in properties of the exopolymeric substances at the interface of the oxygenic and anoxygenic photoautotrophic layers and (ii) the synergy between two major players of sulfur cycle, purple sulfur bacteria, and sulfate-reducing bacteria. The repetition of this process over time combined with upward growth of the mat is a possible pathway leading to the formation of a stromatolite.

Ultrafine Cobalt Catalysts on Covalent Carbon Nitride Frameworks for Oxygenic Photosynthesis

The rational cooperation of sustainable catalysts with suitable light-harvesting semiconductors to fabricate photosynthetic device/machinery has been regarded as an ideal technique to alleviate the current worldwide energy and environmental issues. Cobalt based species (e.g., Co-Pi, Co3O4, and Co-cubene) have attracted particular attentions because they are earth-abundant, cost-acceptable, and more importantly, it shows comparable water oxidation activities to the noble metal based catalysts (e.g., RuO2, IrO2). In this contribution, we compared two general cocatalysts modification strategies, based on the surface depositing and bulk doping of ultrafine cobalt species into the sustainable graphitic carbon nitride (g-C3N4) polymer networks for oxygenic photosynthesis by splitting water into oxygen, electrons, and protons. The chemical backbone of g-C3N4 does not alter after both engineering modifications; however, in comparison with the bulk doping, the optical and electronic properties of the surface depositing samples are efficiently promoted, and the photocatalytic water oxidation activities are increased owing to much more exposed active sites, reduced overpotential for oxygen evolution and the accelerated interface charge mobility. This paper underlines the advantage of surface engineering to establish efficient advanced polymeric composites for water oxidation, and it opens new insights into the architectural design of binary hybrid photocatalysts with high reactivity and further utilizations in the fields of energy and environment.

Reconstructing the Origin of Oxygenic Photosynthesis: Do Assembly and Photoactivation Recapitulate Evolution?

Due to the great abundance of genomes and protein structures that today span a broad diversity of organisms, now more than ever before, it is possible to reconstruct the molecular evolution of protein complexes at an incredible level of detail. Here, I recount the story of oxygenic photosynthesis or how an ancestral reaction center was transformed into a sophisticated photochemical machine capable of water oxidation. First, I review the evolution of all reaction center proteins in order to highlight that Photosystem II and Photosystem I, today only found in the phylum Cyanobacteria, branched out very early in the history of photosynthesis. Therefore, it is very unlikely that they were acquired via horizontal gene transfer from any of the described phyla of anoxygenic phototrophic bacteria. Second, I present a new evolutionary scenario for the origin of the CP43 and CP47 antenna of Photosystem II. I suggest that the antenna proteins originated from the remodeling of an entire Type I reaction center protein and not from the partial gene duplication of a Type I reaction center gene. Third, I highlight how Photosystem II and Photosystem I reaction center proteins interact with small peripheral subunits in remarkably similar patterns and hypothesize that some of this complexity may be traced back to the most ancestral reaction center. Fourth, I outline the sequence of events that led to the origin of the Mn4CaO5 cluster and show that the most ancestral Type II reaction center had some of the basic structural components that would become essential in the coordination of the water-oxidizing complex. Finally, I collect all these ideas, starting at the origin of the first reaction center proteins and ending with the emergence of the water-oxidizing cluster, to hypothesize that the complex and well-organized process of assembly and photoactivation of Photosystem II recapitulate evolutionary transitions in the path to oxygenic photosynthesis.

Reappraisal of hydrocarbon biomarkers in Archean rocks

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 (<37.9 pg per gram of rock) and total sterane (<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.

Origin and Evolution of Water Oxidation before the Last Common Ancestor of the Cyanobacteria

Photosystem II, the water oxidizing enzyme, altered the course of evolution by filling the atmosphere with oxygen. Here, we reconstruct the origin and evolution of water oxidation at an unprecedented level of detail by studying the phylogeny of all D1 subunits, the main protein coordinating the water oxidizing cluster (Mn₄CaO₅) of Photosystem II. We show that D1 exists in several forms making well-defined clades, some of which could have evolved before the origin of water oxidation and presenting many atypical characteristics. The most ancient form is found in the genome of Gloeobacter kilaueensis JS-1 and this has a C-terminus with a higher sequence identity to D2 than to any other D1. Two other groups of early evolving D1 correspond to those expressed under prolonged far-red illumination and in darkness. These atypical D1 forms are characterized by a dramatically different Mn₄CaO₅ binding site and a Photosystem II containing such a site may assemble an unconventional metal cluster. The first D1 forms with a full set of ligands to the Mn₄CaO₅ cluster are grouped with D1 proteins expressed only under low oxygen concentrations and the latest evolving form is the dominant type of D1 found in all cyanobacteria and plastids. In addition, we show that the plastid ancestor had a D1 more similar to those in early branching Synechococcus. We suggest each one of these forms of D1 originated from transitional forms at different stages toward the innovation and optimization of water oxidation before the last common ancestor of all known cyanobacteria.

Benthic perspective on Earth's oldest evidence for oxygenic photosynthesis

The Great Oxidation Event (GOE) is currently viewed as a protracted process during which atmospheric oxygen increased above ∼10(-5) times the present atmospheric level (PAL). This threshold represents an estimated upper limit for sulfur isotope mass-independent fractionation (S-MIF), an Archean signature of atmospheric anoxia that begins to disappear from the rock record at 2.45 Ga. However, an increasing number of papers have suggested that the timing for oxidative continental weathering, and by conventional thinking the onset of atmospheric oxygenation, was hundreds of million years earlier than previously thought despite the presence of S-MIF. We suggest that this apparent discrepancy can be resolved by the earliest oxidative-weathering reactions occurring in benthic and soil environments at profound redox disequilibrium with the atmosphere, such as biological soil crusts and freshwater microbial mats covering riverbed, lacustrine, and estuarine sediments. We calculate that oxygenic photosynthesis in these millimeter-thick ecosystems provides sufficient oxidizing equivalents to mobilize sulfate and redox-sensitive trace metals from land to the oceans while the atmosphere itself remained anoxic with its attendant S-MIF signature. As continental freeboard increased significantly between 3.0 and 2.5 Ga, the chemical and isotopic signatures of benthic oxidative weathering would have become more globally significant from a mass-balance perspective. These observations help reconcile evidence for pre-GOE oxidative weathering with the history of atmospheric chemistry, and support the plausible antiquity of a terrestrial biosphere populated by cyanobacteria well before the GOE.

The evolution of autotrophy in relation to phosphorus requirement

The evolution of autotrophy is considered in relation to the availability of phosphorus (P), the ultimate elemental resource limiting biological productivity through Earth's history. Work on microbes and plants is emphasized, dealing in turn with the main uses for P in cells, namely nucleic acids, phospholipids, and water-soluble low molecular mass phosphate esters plus metabolically active inorganic orthophosphate. There is a greater minimum gene number and minimum DNA content in autotrophic than in osmochemoorganotrophic archaea and bacteria, as well as a lower rate of biomass increase per unit P (P-use efficiency) in autotrophs than in osmochemoorganotrophs, in eukaryotes as well as bacteria. This may be due to the diversion of rRNA from producing proteins common to all organisms to producing highly expressed proteins specific to autotrophs. The P requirement for phospholipids is decreased in oxygenic photolithotrophs, and some anoxygenic photolithotrophs, by substituting galactolipids and sulpholipids for phospholipids in the photosynthetic, and some other, membranes. The six different autotrophic inorganic carbon assimilation pathways have varying requirements for low molecular mass water-soluble phosphate esters. In oxygenic photolithotrophs, there is no clear evidence of a different P requirement for growth in the absence (diffusive CO2 entry) relative to the presence of CO2-concentrating mechanisms (CCMs). P limitation increases the expression of crassulacean acid metabolism (CAM) in facultative CAM plants, decreases the extent of inorganic carbon accumulation in algae with CCMs, and (usually) their inorganic carbon affinity and the water-use efficiency of growth of terrestrial plants, and the light-use efficiency of photolithotrophs.

Evolutionary origins of the photosynthetic water oxidation cluster: bicarbonate permits Mn(2+) photo-oxidation by anoxygenic bacterial reaction centers

The enzyme that catalyzes water oxidation in oxygenic photosynthesis contains an inorganic cluster (Mn4 CaO5 ) that is universally conserved in all photosystem II (PSII) protein complexes. Its hypothesized precursor is an anoxygenic photobacterium containing a type 2 reaction center as photo-oxidant (bRC2, iron-quinone type). Here we provide the first experimental evidence that a native bRC2 complex can catalyze the photo-oxidation of Mn(2+) to Mn(3+) , but only in the presence of bicarbonate concentrations that allows the formation of (bRC2)Mn(2+) (bicarbonate)1-2 complexes. Parallel-mode EPR spectroscopy was used to characterize the photoproduct, (bRC2)Mn(3+) (CO3 (2-) ), based on the g tensor and (55) Mn hyperfine splitting. (Bi)carbonate coordination extends the lifetime of the Mn(3+) photoproduct by slowing charge recombination. Prior electrochemical measurements show that carbonate complexation thermodynamically stabilizes the Mn(3+) product by 0.9-1 V relative to water ligands. A model for the origin of the water oxidation catalyst is presented that proposes chemically feasible steps in the evolution of oxygenic PSIIs, and is supported by literature results on the photoassembly of contemporary PSIIs.

Interactions of photosynthesis with genome size and function

Photolithotrophs are divided between those that use water as their electron donor (Cyanobacteria and the photosynthetic eukaryotes) and those that use a different electron donor (the anoxygenic photolithotrophs, all of them Bacteria). Photolithotrophs with the most reduced genomes have more genes than do the corresponding chemoorganotrophs, and the fastest-growing photolithotrophs have significantly lower specific growth rates than the fastest-growing chemoorganotrophs. Slower growth results from diversion of resources into the photosynthetic apparatus, which accounts for about half of the cell protein. There are inherent dangers in (especially oxygenic) photosynthesis, including the formation of reactive oxygen species (ROS) and blue light sensitivity of the water spitting apparatus. The extent to which photolithotrophs incur greater DNA damage and repair, and faster protein turnover with increased rRNA requirement, needs further investigation. A related source of environmental damage is ultraviolet B (UVB) radiation (280-320 nm), whose flux at the Earth's surface decreased as oxygen (and ozone) increased in the atmosphere. This oxygenation led to the requirements of defence against ROS, and decreasing availability to organisms of combined (non-dinitrogen) nitrogen and ferrous iron, and (indirectly) phosphorus, in the oxygenated biosphere. Differential codon usage in the genome and, especially, the proteome can lead to economies in the use of potentially growth-limiting elements.

Lycopene cyclase paralog CruP protects against reactive oxygen species in oxygenic photosynthetic organisms

In photosynthetic organisms, carotenoids serve essential roles in photosynthesis and photoprotection. A previous report designated CruP as a secondary lycopene cyclase involved in carotenoid biosynthesis [Maresca J, et al. (2007) Proc Natl Acad Sci USA 104:11784-11789]. However, we found that cruP KO or cruP overexpression plants do not exhibit correspondingly reduced or increased production of cyclized carotenoids, which would be expected if CruP was a lycopene cyclase. Instead, we show that CruP aids in preventing accumulation of reactive oxygen species (ROS), thereby reducing accumulation of β-carotene-5,6-epoxide, a ROS-catalyzed autoxidation product, and inhibiting accumulation of anthocyanins, which are known chemical indicators of ROS. Plants with a nonfunctional cruP accumulate substantially higher levels of ROS and β-carotene-5,6-epoxide in green tissues. Plants overexpressing cruP show reduced levels of ROS, β-carotene-5,6-epoxide, and anthocyanins. The observed up-regulation of cruP transcripts under photoinhibitory and lipid peroxidation-inducing conditions, such as high light stress, cold stress, anoxia, and low levels of CO(2), fits with a role for CruP in mitigating the effects of ROS. Phylogenetic distribution of CruP in prokaryotes showed that the gene is only present in cyanobacteria that live in habitats characterized by large variation in temperature and inorganic carbon availability. Therefore, CruP represents a unique target for developing resilient plants and algae needed to supply food and biofuels in the face of global climate change.

Algal photosynthesis as the primary driver for a sustainable development in energy, feed, and food production

High oil prices and global warming that accompany the use of fossil fuels are an incentive to find alternative forms of energy supply. Photosynthetic biofuel production represents one of these since for this, one uses renewable resources. Sunlight is used for the conversion of water and CO₂ into biomass. Two strategies are used in parallel: plant-based production via sugar fermentation into ethanol and biodiesel production through transesterification. Both, however, exacerbate other problems, including regional nutrient balancing and the world's food supply, and suffer from the modest efficiency of photosynthesis. Maximizing the efficiency of natural and engineered photosynthesis is therefore of utmost importance. Algal photosynthesis is the system of choice for this particularly for energy applications. Complete conversion of CO₂ into biomass is not necessary for this. Innovative methods of synthetic biology allow one to combine photosynthetic and fermentative metabolism via the so-called Photanol approach to form biofuel directly from Calvin cycle intermediates through use of the naturally transformable cyanobacterium Synechocystis sp. PCC 6803. Beyond providing transport energy and chemical feedstocks, photosynthesis will continue to be used for food and feed applications. Also for this application, arguments of efficiency will become more and more important as the size of the world population continues to increase. Photosynthetic cells can be used for food applications in various innovative forms, e.g., as a substitute for the fish proteins in the diet supplied to carnivorous fish or perhaps--after acid hydrolysis--as a complex, animal-free serum for growth of mammalian cells in vitro.

On-line mass spectrometry: membrane inlet sampling

Significant insights into plant photosynthesis and respiration have been achieved using membrane inlet mass spectrometry (MIMS) for the analysis of stable isotope distribution of gases. The MIMS approach is based on using a gas permeable membrane to enable the entry of gas molecules into the mass spectrometer source. This is a simple yet durable approach for the analysis of volatile gases, particularly atmospheric gases. The MIMS technique strongly lends itself to the study of reaction flux where isotopic labeling is employed to differentiate two competing processes; i.e., O(2) evolution versus O(2) uptake reactions from PSII or terminal oxidase/rubisco reactions. Such investigations have been used for in vitro studies of whole leaves and isolated cells. The MIMS approach is also able to follow rates of isotopic exchange, which is useful for obtaining chemical exchange rates. These types of measurements have been employed for oxygen ligand exchange in PSII and to discern reaction rates of the carbonic anhydrase reactions. Recent developments have also engaged MIMS for online isotopic fractionation and for the study of reactions in inorganic systems that are capable of water splitting or H(2) generation. The simplicity of the sampling approach coupled to the high sensitivity of modern instrumentation is a reason for the growing applicability of this technique for a range of problems in plant photosynthesis and respiration. This review offers some insights into the sampling approaches and and the experiments that have been conducted with MIMS.