The Photosynthetic Apparatus and Its Regulation in the Aerobic Gammaproteobacterium Congregibacter litoralis gen. nov., sp. nov

BACKGROUND: There is accumulating evidence that in some marine environments aerobic bacteriochlorophyll a-producing bacteria represent a significant part of the microbial population. The interaction of photosynthesis and carbon metabolism in these interesting bacteria is still largely unknown and requires further investigation in order to estimate their contribution to the marine carbon cycle. METHODOLOGY/PRINCIPAL FINDINGS: Here, we analyzed the structure, composition and regulation of the photosynthetic apparatus in the obligately aerobic marine gammaproteobacterium KT71(T). Photoheterotrophically grown cells were characterized by a poorly developed lamellar intracytoplasmic membrane system, a type 1 light-harvesting antenna complex and a photosynthetic reaction center associated with a tetraheme cytochrome c. The only photosynthetic pigments produced were bacteriochlorophyll a and spirilloxanthin. Under semiaerobic conditions KT71(T) cells expressing a photosynthetic apparatus showed a light-dependent increase of growth yield in the range of 1.3-2.5 fold. The expression level of the photosynthetic apparatus depended largely on the utilized substrate, the intermediary carbon metabolism and oxygen tension. In addition, pigment synthesis was strongly influenced by light, with blue light exerting the most significant effect, implicating that proteins containing a BLUF domain may be involved in regulation of the photosynthetic apparatus. Several phenotypic traits in KT71(T) could be identified that correlated with the assumed redox state of growing cells and thus could be used to monitor the cellular redox state under various incubation conditions. CONCLUSIONS/SIGNIFICANCE: In a hypothetical model that explains the regulation of the photosynthetic apparatus in strain KT71(T) we propose that the expression of photosynthesis genes depends on the cellular redox state and is maximal under conditions that allow a balanced membrane redox state. So far, bacteria capable of an obligately aerobic, photosynthetic metabolism constitute a unique phenotype within the class Gammaproteobacteria, so that it is justified to propose a new genus and species, Congregibacter litoralis gen. nov, sp. nov., represented by the type strain KT71(T) ( = DSM 17192(T) = NBRC 104960(T))

A Bioelectrochemical Approach to Characterize Extracellular Electron Transfer by Synechocystis sp. PCC6803

Biophotovoltaic devices employ photosynthetic organisms at the anode of a microbial fuel cell to generate electrical power. Although a range of cyanobacteria and algae have been shown to generate photocurrent in devices of a multitude of architectures, mechanistic understanding of extracellular electron transfer by phototrophs remains minimal. Here we describe a mediatorless bioelectrochemical device to measure the electrogenic output of a planktonically grown cyanobacterium, Synechocystis sp. PCC6803. Light dependent production of current is measured, and its magnitude is shown to scale with microbial cell concentration and light intensity. Bioelectrochemical characterization of a Synechocystis mutant lacking Photosystem II demonstrates conclusively that production of the majority of photocurrent requires a functional water splitting aparatus and electrons are likely ultimately derived from water. This shows the potential of the device to rapidly and quantitatively characterize photocurrent production by genetically modified strains, an approach that can be used in future studies to delineate the mechanisms of cyanobacterial extracellular electron transport

Predicting the Electron Requirement for Carbon Fixation in Seas and Oceans

Marine phytoplankton account for about 50% of all global net primary productivity (NPP). Active fluorometry, mainly Fast Repetition Rate fluorometry (FRRf), has been advocated as means of providing high resolution estimates of NPP. However, not measuring CO2-fixation directly, FRRf instead provides photosynthetic quantum efficiency estimates from which electron transfer rates (ETR) and ultimately CO2-fixation rates can be derived. Consequently, conversions of ETRs to CO2-fixation requires knowledge of the electron requirement for carbon fixation (Φe,C, ETR/CO2 uptake rate) and its dependence on environmental gradients. Such knowledge is critical for large scale implementation of active fluorescence to better characterise CO2-uptake. Here we examine the variability of experimentally determined Φe,C values in relation to key environmental variables with the aim of developing new working algorithms for the calculation of Φe,C from environmental variables. Coincident FRRf and 14C-uptake and environmental data from 14 studies covering 12 marine regions were analysed via a meta-analytical, non-parametric, multivariate approach. Combining all studies, Φe,C varied between 1.15 and 54.2 mol e- (mol C)-1 with a mean of 10.9±6.91 mol e- mol C)-1. Although variability of Φe,C was related to environmental gradients at global scales, region-specific analyses provided far improved predictive capability. However, use of regional Φe,C algorithms requires objective means of defining regions of interest, which remains challenging. Considering individual studies and specific small-scale regions, temperature, nutrient and light availability were correlated with Φe,C albeit to varying degrees and depending on the study/region and the composition of the extant phytoplankton community. At the level of large biogeographic regions and distinct water masses, Φe,C was related to nutrient availability, chlorophyll, as well as temperature and/or salinity in most regions, while light availability was also important in Baltic Sea and shelf waters. The novel Φe,C algorithms provide a major step forward for widespread fluorometry-based NPP estimates and highlight the need for further studying the natural variability of Φe,C to verify and develop algorithms with improved accuracy. © 2013 Lawrenz et al

High ultraviolet C resistance of marine Planctomycetes

Planctomycetes are bacteria with particular characteristics such as internal membrane systems encompassing intracellular compartments, proteinaceous cell walls, cell division by yeast-like budding and large genomes. These bacteria inhabit a wide range of habitats, including marine ecosystems, in which ultra-violet radiation has a potential harmful impact in living organisms. To evaluate the effect of ultra-violet C on the genome of several marine strains of Planctomycetes, we developed an easy and fast DNA diffusion assay in which the cell wall was degraded with papain, the wall-free cells were embedded in an agarose microgel and lysed. The presence of double strand breaks and unwinding by single strand breaks allow DNA diffusion, which is visible as a halo upon DNA staining. The number of cells presenting DNA diffusion correlated with the dose of ultra-violet C or hydrogen peroxide. From DNA damage and viability experiments, we found evidence indicating that some strains of Planctomycetes are significantly resistant to ultra-violet C radiation, showing lower sensitivity than the known resistant Arthrobacter sp. The more resistant strains were those phylogenetically closer to Rhodopirellula baltica, suggesting that these species are adapted to habitats under the influence of ultra-violet radiation. Our results provide evidence indicating that the mechanism of resistance involves DNA damage repair and/or other DNA ultra-violet C-protective mechanism.This research was supported by the European Regional Development Fund (ERDF) through the COMPETE-Operational Competitiveness Programme and national funds through FCT-Foundation for Science and Technology, under the projects Pest-C/BIA/UI4050/2011 and PEst-C/MAR/LA0015/2013. We are grateful to Catia Moreira for helping with the extraction of the pigments.info:eu-repo/semantics/publishedVersio

Diverse Arrangement of Photosynthetic Gene Clusters in Aerobic Anoxygenic Phototrophic Bacteria

BACKGROUND: Aerobic anoxygenic photototrophic (AAP) bacteria represent an important group of marine microorganisms inhabiting the euphotic zone of the ocean. They harvest light using bacteriochlorophyll (BChl) a and are thought to be important players in carbon cycling in the ocean. METHODOLOGY/PRINCIPAL FINDINGS: Aerobic anoxygenic phototrophic (AAP) bacteria represent an important part of marine microbial communities. Their photosynthetic apparatus is encoded by a number of genes organized in a so-called photosynthetic gene cluster (PGC). In this study, the organization of PGCs was analyzed in ten AAP species belonging to the orders Rhodobacterales, Sphingomonadales and the NOR5/OM60 clade. Sphingomonadales contained comparatively smaller PGCs with an approximately size of 39 kb whereas the average size of PGCs in Rhodobacterales and NOR5/OM60 clade was about 45 kb. The distribution of four arrangements, based on the permutation and combination of the two conserved regions bchFNBHLM-LhaA-puhABC and crtF-bchCXYZ, does not correspond to the phylogenetic affiliation of individual AAP bacterial species. While PGCs of all analyzed species contained the same set of genes for bacteriochlorophyll synthesis and assembly of photosynthetic centers, they differed largely in the carotenoid biosynthetic genes. Spheroidenone, spirilloxanthin, and zeaxanthin biosynthetic pathways were found in each clade respectively. All of the carotenoid biosynthetic genes were found in the PGCs of Rhodobacterales, however Sphingomonadales and NOR5/OM60 strains contained some of the carotenoid biosynthetic pathway genes outside of the PGC. CONCLUSIONS/SIGNIFICANCE: Our investigations shed light on the evolution and functional implications in PGCs of marine aerobic anoxygenic phototrophs, and support the notion that AAP are a heterogenous physiological group phylogenetically scattered among Proteobacteria

Photoacclimation in Dunaliella tertiolecta reveals a unique NPQ pattern upon exposure to irradiance

Highly time-resolved photoacclimation patterns of the chlorophyte microalga Dunaliella tertiolecta during exposure to an off–on–off (block) light pattern of saturating photon flux, and to a regime of consecutive increasing light intensities are presented. Non-photochemical quenching (NPQ) mechanisms unexpectedly responded with an initial decrease during dark–light transitions. NPQ values started to rise after light exposure of approximately 4 min. State-transitions, measured as a change of PSII:PSI fluorescence emission at 77 K, did not contribute to early NPQ oscillations. Addition of the uncoupler CCCP, however, caused a rapid increase in fluorescence and showed the significance of qE for NPQ. Partitioning of the quantum efficiencies showed that constitutive NPQ was (a) higher than qE-driven NPQ and (b) responded to light treatment within seconds, suggesting an active role of constitutive NPQ in variable energy dissipation, although it is thought to contribute statically to NPQ. The PSII connectivity parameter p correlated well with F′, Fm′ and NPQ during the early phase of the dark–light transients in sub-saturating light, suggesting a plastic energy distribution pattern within energetically connected PSII centres. In consecutive increasing photon flux experiments, correlations were weaker during the second light increment. Changes in connectivity can present an early photoresponse that are reflected in fluorescence signals and NPQ and might be responsive to the short-term acclimation state, and/or to the actinic photon flux

Planktonic Microbes in the Gulf of Maine Area

In the Gulf of Maine area (GoMA), as elsewhere in the ocean, the organisms of greatest numerical abundance are microbes. Viruses in GoMA are largely cyanophages and bacteriophages, including podoviruses which lack tails. There is also evidence of Mimivirus and Chlorovirus in the metagenome. Bacteria in GoMA comprise the dominant SAR11 phylotype cluster, and other abundant phylotypes such as SAR86-like cluster, SAR116-like cluster, Roseobacter, Rhodospirillaceae, Acidomicrobidae, Flavobacteriales, Cytophaga, and unclassified Alphaproteobacteria and Gammaproteobacteria clusters. Bacterial epibionts of the dinoflagellate Alexandrium fundyense include Rhodobacteraceae, Flavobacteriaceae, Cytophaga spp., Sulfitobacter spp., Sphingomonas spp., and unclassified Bacteroidetes. Phototrophic prokaryotes in GoMA include cyanobacteria that contain chlorophyll (mainly Synechococcus), aerobic anoxygenic phototrophs that contain bacteriochlorophyll, and bacteria that contain proteorhodopsin. Eukaryotic microalgae in GoMA include Bacillariophyceae, Dinophyceae, Prymnesiophyceae, Prasinophyceae, Trebouxiophyceae, Cryptophyceae, Dictyochophyceae, Chrysophyceae, Eustigmatophyceae, Pelagophyceae, Synurophyceae, and Xanthophyceae. There are no records of Bolidophyceae, Aurearenophyceae, Raphidophyceae, and Synchromophyceae in GoMA. In total, there are records for 665 names and 229 genera of microalgae. Heterotrophic eukaryotic protists in GoMA include Dinophyceae, Alveolata, Apicomplexa, amoeboid organisms, Labrynthulida, and heterotrophic marine stramenopiles (MAST). Ciliates include Strombidium, Lohmaniella, Tontonia, Strobilidium, Strombidinopsis and the mixotrophs Laboea strobila and Myrionecta rubrum (ex Mesodinium rubra). An inventory of selected microbial groups in each of 14 physiographic regions in GoMA is made by combining information on the depth-dependent variation of cell density and the depth-dependent variation of water volume. Across the entire GoMA, an estimate for the minimum abundance of cell-based microbes is 1.7×1025 organisms. By one account, this number of microbes implies a richness of 105 to 106 taxa in the entire water volume of GoMA. Morphological diversity in microplankton is well-described but the true extent of taxonomic diversity, especially in the femtoplankton, picoplankton and nanoplankton – whether autotrophic, heterotrophic, or mixotrophic, is unknown

Gain and Loss of Phototrophic Genes Revealed by Comparison of Two Citromicrobium Bacterial Genomes

Proteobacteria are thought to have diverged from a phototrophic ancestor, according to the scattered distribution of phototrophy throughout the proteobacterial clade, and so the occurrence of numerous closely related phototrophic and chemotrophic microorganisms may be the result of the loss of genes for phototrophy. A widespread form of bacterial phototrophy is based on the photochemical reaction center, encoded by puf and puh operons that typically are in a ‘photosynthesis gene cluster’ (abbreviated as the PGC) with pigment biosynthesis genes. Comparison of two closely related Citromicrobial genomes (98.1% sequence identity of complete 16S rRNA genes), Citromicrobium sp. JL354, which contains two copies of reaction center genes, and Citromicrobium strain JLT1363, which is chemotrophic, revealed evidence for the loss of phototrophic genes. However, evidence of horizontal gene transfer was found in these two bacterial genomes. An incomplete PGC (pufLMC-puhCBA) in strain JL354 was located within an integrating conjugative element, which indicates a potential mechanism for the horizontal transfer of genes for phototrophy

Phylogenomic Analysis of Marine Roseobacters

Background: Members of the Roseobacter clade which play a key role in the biogeochemical cycles of the ocean are diverse and abundant, comprising 10–25 % of the bacterioplankton in most marine surface waters. The rapid accumulation of whole-genome sequence data for the Roseobacter clade allows us to obtain a clearer picture of its evolution. Methodology/Principal Findings: In this study about 1,200 likely orthologous protein families were identified from 17 Roseobacter bacteria genomes. Functional annotations for these genes are provided by iProClass. Phylogenetic trees were constructed for each gene using maximum likelihood (ML) and neighbor joining (NJ). Putative organismal phylogenetic trees were built with phylogenomic methods. These trees were compared and analyzed using principal coordinates analysis (PCoA), approximately unbiased (AU) and Shimodaira–Hasegawa (SH) tests. A core set of 694 genes with vertical descent signal that are resistant to horizontal gene transfer (HGT) is used to reconstruct a robust organismal phylogeny. In addition, we also discovered the most likely 109 HGT genes. The core set contains genes that encode ribosomal apparatus, ABC transporters and chaperones often found in the environmental metagenomic and metatranscriptomic data. These genes in the core set are spread out uniformly among the various functional classes and biological processes. Conclusions/Significance: Here we report a new multigene-derived phylogenetic tree of the Roseobacter clade. Of particular interest is the HGT of eleven genes involved in vitamin B12 synthesis as well as key enzynmes fo