Isolation of Aerobic Anoxygenic Photosynthetic Bacteria from Black Smoker Plume Waters of the Juan de Fuca Ridge in the Pacific Ocean

A strain of the aerobic anoxygenic photosynthetic bacteria was isolated from a deep-ocean hydrothermal vent plume environment. The in vivo absorption spectra of cells indicate the presence of bacteriochlorophyll a incorporated into light-harvesting complex I and a reaction center. The general morphological and physiological characteristics of this new isolate are described.     

Roseobacter-Like Bacteria in Red and Mediterranean Sea Aerobic Anoxygenic Photosynthetic Populations

Bacteriochlorophyll a-containing aerobic anoxygenic phototrophs (AAnP) have been proposed to account for up to 11% of the total surface water microbial community and to potentially have great ecological importance in the world's oceans. Recently, environmental and genomic data based on analysis of the pufM gene identified the existence of α-proteobacteria as well as possible γ-like proteobacteria among AAnP in the Pacific Ocean. Here we report on analyses of environmental samples from the Red and Mediterranean Seas by using pufM as well as the bchX and bchL genes as molecular markers. The majority of photosynthesis genes retrieved from these seas were related to Roseobacter-like AAnP sequences. Furthermore, the sequence of a novel photosynthetic operon organization from an uncultured Roseobacter-like bacterial artificial chromosome retrieved from the Red Sea is described. The data show the presence of Roseobacter-like bacteria in Red and Mediterranean Sea AAnP populations in the seasons analyzed.     

Aerobic Anoxygenic Phototrophic Bacteria in the Mid-Atlantic Bight and the North Pacific Gyre

The abundance of aerobic anoxygenic phototrophic (AAP) bacteria, cyanobacteria, and heterotrophs was examined in the Mid-Atlantic Bight and the central North Pacific Gyre using infrared fluorescence microscopy coupled with image analysis and flow cytometry. AAP bacteria comprised 5% to 16% of total prokaryotes in the Atlantic Ocean but only 5% or less in the Pacific Ocean. In the Atlantic, AAP bacterial abundance was as much as 2-fold higher than that of Prochlorococcus spp. and 10-fold higher than that of Synechococcus spp. In contrast, Prochlorococcus spp. outnumbered AAP bacteria 5- to 50-fold in the Pacific. In both oceans, subsurface abundance maxima occurred within the photic zone, and AAP bacteria were least abundant below the 1% light depth. The abundance of AAP bacteria rivaled some groups of strictly heterotrophic bacteria and was often higher than the abundance of known AAP bacterial genera (Erythrobacter and Roseobacter spp.). Concentrations of bacteriochlorophyll a (BChl a) were low (~1%) compared to those of chlorophyll a in the North Atlantic. Although the BChl a content of AAP bacteria per cell was typically 20- to 250-fold lower than the divinyl-chlorophyll a content of Prochlorococcus, the pigment content of AAP bacteria approached that of Prochlorococcus in shelf break water. Our results suggest that AAP bacteria can be quite abundant in some oceanic regimes and that their distribution in the water column is consistent with phototrophy.     

Aerobic Anoxygenic Photosynthesis in Roseobacter Clade Bacteria from Diverse Marine Habitats

The marine Roseobacter clade comprises several genera of marine bacteria related to the uncultured SAR83 cluster, the second most abundant marine picoplankton lineage. Cultivated representatives of this clade are physiologically heterogeneous, and only some have the capability for aerobic anoxygenic photosynthesis, a process of potentially great ecological importance in the world's oceans. In an attempt to correlate phylogeny with ecology, we investigated the diversity of Roseobacter clade strains from various marine habitats (water samples, biofilms, laminariae, diatoms, and dinoflagellate cultures) by using the 16S rRNA gene as a phylogenetic marker gene. The potential for aerobic anoxygenic photosynthesis was determined on the genetic level by PCR amplification and sequencing of the pufLM genes of the bacterial photosynthesis reaction center and on the physiological level by detection of bacteriochlorophyll (Bchl) a. A collection of ca. 1,000 marine isolates was screened for members of the marine Roseobacter clade by 16S rRNA gene-directed multiplex PCR and sequencing. The 42 Roseobacter clade isolates found tended to form habitat-specific subclusters. The pufLM genes were detected in two groups of strains from dinoflagellate cultures but in none of the other Roseobacter clade isolates. Strains within the first group (the DFL-12 cluster) also synthesized Bchl a. Strains within the second group (the DFL-35 cluster) formed a new species of Roseovarius and did not produce Bchl a under the conditions investigated here, thus demonstrating the importance of genetic methods for screening of cultivation-dependent metabolic traits. The pufL genes of the dinoflagellate isolates were phylogenetically closely related to pufL genes from Betaproteobacteria, confirming similar previous observations which have been interpreted as indications of gene transfer events.     

High abundances of aerobic anoxygenic photosynthetic bacteria in the South Pacific Ocean

Little is known about the abundance, distribution, and ecology of aerobic anoxygenic phototrophic (AAP) bacteria, particularly in oligotrophic environments, which represent 60% of the ocean. We investigated the abundance of AAP bacteria across the South Pacific Ocean, including the center of the gyre, the most oligotrophic water body of the world ocean. AAP bacteria, Prochlorococcus, and total prokaryotic abundances, as well as bacteriochlorophyll a (BChl a) and divinyl-chlorophyll a concentrations, were measured at several depths in the photic zone along a gradient of oligotrophic conditions. The abundances of AAP bacteria and Prochlorococcus were high, together accounting for up to 58% of the total prokaryotic community. The abundance of AAP bacteria alone was up to 1.94 x 10(5) cells ml(-1) and as high as 24% of the overall community. These measurements were consistent with the high BChl a concentrations (up to 3.32 x 10(-3) microg liter(-1)) found at all stations. However, the BChl a content per AAP bacterial cell was low, suggesting that AAP bacteria are mostly heterotrophic organisms. Interestingly, the biovolume and therefore biomass of AAP bacteria was on average twofold higher than that of other prokaryotic cells. This study demonstrates that AAP bacteria can be abundant in various oligotrophic conditions, including the most oligotrophic regime of the world ocean, and can account for a large part of the bacterioplanktonic carbon stock.     

BchY-Based Degenerate Primers Target All Types of Anoxygenic Photosynthetic Bacteria in a Single PCR

To detect anoxygenic bacteria containing either type 1 or type 2 photosynthetic reaction centers in a single PCR, we designed a degenerate primer set based on the bchY gene. The new primers were validated in silico using the GenBank nucleotide database as well as by PCR on pure strains and environmental DNA.Anoxygenic photosynthetic bacteria are diverse and important members of microbial communities (11, 13, 17, 20). There are five bacterial phyla containing anoxygenic phototrophs: Proteobacteria (purple bacteria), Chlorobi (green sulfur bacteria), Chloroflexi (green nonsulfur bacteria), Acidobacteria (“Candidatus Chloracidobacterium thermophilum” [7]), and Firmicutes (heliobacteria). While Heliobacterium modesticaldum, Chlorobi, and “Ca. Chloracidobacterium thermophilum” have a type 1 reaction center (RC1) similar to photosystem I in Cyanobacteria and higher plants, Chloroflexi and Proteobacteria possess a type 2 reaction center (RC2) similar to photosystem II of oxygenic phototrophs (7, 16).Primers based on pufM, the gene encoding the M subunit of RC2, have been widely used to detect phototrophic purple bacteria (1, 4, 12, 19). However, phototrophic bacteria that do not possess RC2 are not retrieved when pufM is used as the target. Achenbach and coworkers (1) developed primers targeting rRNA genes of Chlorobi, Chloroflexi, and heliobacteria, while Alexander and coworkers (2) have developed primers to specifically detect green sulfur bacteria (Chlorobi) by using 16S rRNA and fmoA as gene targets and applied these primers in environmental studies (3). No currently available primer set can simultaneously target phototrophs containing either RC1 or RC2.Since it is well established that both RC1- and RC2-containing anoxygenic phototrophs synthesize bacteriochlorophylls (BChls), we searched for a universal anoxygenic photosynthesis gene marker among all enzymes involved in BChl biosynthetic pathways. All known pathways for chlorophyll and BChl biosynthesis branch from the heme biosynthesis pathway at protoporphyrin IX and continue to chlorophyllide a (Chlide a) through the same intermediates (9). Chlide a is the branching point that separates chlorophyll and BChl biosynthetic pathways. Moreover, pathways for the synthesis of different BChls are also split at this stage: chlorophyllide oxidoreductase converts Chlide a to 3-vinyl-bacteriophyllide a, which is the precursor for BChls a, b, and g, while a yet unknown enzyme reduces Chlide a to 3-vinyl-bacteriophyllide d, a precursor for antenna BChls c, d, and e in Chlorobium spp. (9). Since 3-vinyl-bacteriophyllide a is the last common intermediate in the synthesis of BChl a and BChl g, and the latter is the only BChl in heliobacteria (14, 15), chlorophyllide oxidoreductase is the only enzyme that is (i) present in anoxygenic phototrophic bacteria and not in oxygenic phototrophs and (ii) common to all known anoxygenic phototrophic bacterial species (with the exception of “Ca. Chloracidobacterium thermophilum,” where the pathway for BChl synthesis is not yet known). Analyzing multiple alignments of the subunits of chlorophyllide oxidoreductase, we found that only the Y subunit (encoded by the BchY gene) had two conserved regions distinguishing this protein from its closest homologs; therefore, the bchY gene was chosen as a universal marker for anoxygenic photosynthesis.Due to likely codon variations coding identical amino acid sequences in different genomes (19), degenerate BchY primers were designed by reverse translation of two conserved regions of the BchY alignment (Fig. ​(Fig.1):1): bchY_fwd (5′-CCNCARACNATGTGYCCNGCNTTYGG-3′ [26 bases; 2,048 variants; corresponding amino acid sequence, PQTMCPAFG]) and bchY_rev (5′-GGRTCNRCNGGRAANATYTCNCC-3′ [23 bases; 4,096 variants; corresponding amino acid sequence, GE{I/M}FP{A/ V}DP]). Each primer had no more than two bases deviating from known bchY sequences in the GenBank nr database (except for H. modesticaldum) as well as to environmental BchY variants in the GenBank env_nr database. None of these deviations were located in the 3′ ends of the primers (see Tables S2 and S3 in the supplemental material). These primers, therefore, were predicted to amplify a wide diversity of bchY genes under nonstringent PCR conditions (50 to 52°C annealing temperature). The lengths of the expected PCR products were either 480 bp (for green sulfur, green nonsulfur bacteria, and heliobacteria) or 510 bp (for purple bacteria).Open in a separate windowFIG. 1.Multiple-amino-acid alignment of BchY proteins. Sequence abbreviations: R.den, Roseobacter denitrificans (gi|110677524); R.gel, Rubrivivax gelatinosus (gi|29893484); R.cap, Rhodobacter capsulatus (gi|114868); C.lit, Congregibacter litoralis KT 71 (gi|88706663); H.hal, Halorhodospira halophila (gi|121998388); C.aur, Chloroflexus aurantiacus (gi|163849328); C.tep, Chlorobium tepidum (gi|66576270); and H.mod, Heliobacterium modesticaldum (gi|167629410).In order to check primer specificity in silico, a screening procedure was developed. Putative primer sites (tags) for both the bchY_fwd and the bchY_rev primers were gathered from the GenBank nucleotide collection (nt) by BLAST with relaxed search conditions; the tags having mismatches at the 3′ end or more than five overall mismatches from their primer were filtered out, and the remaining tags were mapped to their sequences mimicking PCR primer annealing. Fragments ranging from 300 to 700 bp (virtual “PCR products”) were retrieved from GenBank and annotated (see Table S4 in the supplemental material). All bchY genes present in the GenBank nt database were virtually “amplified,” pointing to the robustness of the primers and our in silico PCR analysis. On the other hand, all nonspecific “amplicons” have major deviations from the primer sequences and would likely not be amplified by a real PCR. The same screening procedure was performed against the GenBank environmental nucleotide collection (env_nt) (see Table S5 in the supplemental material), and as in the case with the nt database, only bchY fragments were virtually “amplified.”The BchY primer set was validated using five key control organisms, including the RC2-containing the purple sulfur bacterium Allochromatium vinosum and the purple nonsulfur bacterium Rhodobacter capsulatus as well as the RC1-containing green sulfur bacterium Chlorobium limicola, green nonsulfur bacterium Chloroflexus aurantiacus, and the heliobacterium H. modesticaldum. Amplifications yielded the predicted products of 510 bp from the purple bacteria and 480 bp from the green sulfur and nonsulfur bacteria and H. modesticaldum. Negative-control Escherichia coli and Synechocystis sp. strain PCC 6803 did not yield amplification products when the bchY primers were used.The designed BchY primer set successfully amplified bchY genes from DNA obtained from both marine (East Mediterranean Sea) and freshwater (Lake Kinneret) environments (see Table S6 in the supplemental material for best BLASTX hits for selected sequenced fragments). These habitats were chosen for testing due to the previously reported wide diversity of their anoxygenic phototrophs (8, 10, 18, 19). A phylogenetic tree of bchY gene fragments amplified from both freshwater and marine DNA samples is shown in Fig. ​Fig.22.Open in a separate windowFIG. 2.BchY phylogenetic tree based on a maximum likelihood tree to which short sequences were added by ARB parsimony. The branches that appeared on the original maximum likelihood tree are shown with thicker lines. Bootstrap values greater than 50% are indicated next to the branches. Sequences obtained in this study are shown in bold. For reasons of clarity, not all BchY sequences retrieved are shown in the tree. For cases in which a BchY fragment was found in more than three clones, the numbers of clones are given in parentheses. Clones m21_2 and m21_3 are identical to the bchY gene of Hoeflea phototrophica strain DFL-43 (6); the m20_2 clone was identical to the bchY gene of Dinoroseobacter shibae (5).Our study underlines the utility of the bchY gene as a molecular marker for revealing genetic heterogeneity in phototrophic microbial populations. Using both wide-scale bioinformatic analysis and PCR on control strains and naturally occurring microbial community DNA, we have confirmed the specificity and coverage of the proposed degenerate BchY primers.     

Aerobic Anoxygenic Phototrophic Bacteria Attached to Particles in Turbid Waters of the Delaware and Chesapeake Estuaries

Aerobic anoxygenic phototrophic (AAP) bacteria are photoheterotrophs that, if abundant, may be biogeochemically important in the oceans. We used epifluorescence microscopy and quantitative PCR (qPCR) to examine the abundance of these bacteria by enumerating cells with bacteriochlorophyll a (bChl a) and the light-reaction center gene pufM, respectively. In the surface waters of the Delaware estuary, AAP bacteria were abundant, comprising up to 34% of prokaryotes, although the percentage varied greatly with location and season. On average, AAP bacteria made up 12% of the community as measured by microscopy and 17% by qPCR. In the surface waters of the Chesapeake, AAP bacteria were less abundant, averaging 6% of prokaryotes. AAP bacterial abundance was significantly correlated with light attenuation (r = 0.50) and ammonium (r = 0.42) and nitrate (r = 0.71) concentrations. Often, bChl a-containing bacteria were mostly attached to particles (31 to 94% of total AAP bacteria), while usually 20% or less of total prokaryotes were associated with particles. Of the cells containing pufM, up to 87% were associated with particles, but the overall average of particle-attached cells was 15%. These data suggest that AAP bacteria are particularly competitive in these two estuaries, in part due to attachment to particles.     

Photosynthetic picoeukaryote community structure in the South East Pacific Ocean encompassing the most oligotrophic waters on Earth

Photosynthetic picoeukaryotes (PPEs), comprising organisms < 3 μm in size, are important primary producers in marine food webs and include representatives from all known algal lineages. Little is known, however, regarding the composition and distribution of PPE communities, particularly at large spatial scales, or in relation to the underlying biotic and abiotic factors that influence this structure. Here, we analysed PPE community structure along a transect in the South East Pacific Ocean (BIOSOPE cruise) that encompassed a large trophic gradient, including hyper‐oligotrophic waters in the South Pacific Gyre (SPG), considered to be some of the ‘clearest’ natural waters on Earth. Using dot blot hybridizations with 16S rRNA oligonucleotide probes, we established that the PPE community was dominated by members of the classes Prymnesiophyceae and Chrysophyceae throughout the transect. Moreover, clone library construction followed by phylogenetic analysis of sequenced clones revealed several novel 16S rRNA gene lineages, including new clades of prymnesiophytes (designated Prym 16S‐III) and prasinophytes (Pras 16S‐VIII). Pras 16S‐VIII was found at all five stations at which clone libraries were constructed, representing a range of trophic conditions, including the South Pacific Gyre, suggesting members of this clade have a broad distribution in this part of the South East Pacific at least. In contrast, Prym 16S‐III sequences were largely restricted to oligotrophic stations of the SPG. Subsequent multivariate statistical analyses showed that, within the measured factors, chemical and biological factors seem to influence PPE community structure more than physical parameters. However, more than 50% of the variation in distribution of PPE classes remained unexplained.     

Carbonic Anhydrase in Anoxygenic Phototrophic Bacteria

Microbiology - The genes encoding carbonic anhydrase (CA) were found in all anoxygenic purple bacteria. The genes of α- and β-CA were found in purple nonsulfur bacteria of the class...     

Tellurite Resistance and Reduction by Obligately Aerobic Photosynthetic Bacteria

Seven species of obligately aerobic photosynthetic bacteria of the genera Erythromicrobium, Erythrobacter, and Roseococcus demonstrated high-level resistance to tellurite and accumulation of metallic tellurium crystals. High-level resistance without tellurite reduction was observed for Roseococcus thiosulfatophilus and Erythromicrobium ezovicum grown with certain organic carbon sources, implying that tellurite reduction is not essential to confer tellurite resistance.     

基于pufM基因的乌梁素海富营养化湖区好氧不产氧光合细菌系统发育多样性分析

好氧不产氧光合细菌(AAPB)的多样性在海洋中已经广泛研究,但在富营养化湖泊中却研究甚少。通过构建和分析AAPB光合中心合成中的关键基因pufM克隆文库,以期揭示乌梁素海富营养化湖区AAPB分布及其系统发育多样性,探讨其在富营养化湖泊中的功能和作用。对乌梁素海红圪卜湖区水体文库中的52个克隆子进行分析,产生了28个OTU,文库覆盖度达到71.4%,反映出文库有较好的代表性。同源性和系统发育分析结果表明,乌梁素海红圪卜湖区AAPB有较高的多样性,与我们之前所发现的同一湖区总细菌多样性较低形成鲜明对比。所获得的序列分属7个亚群,即γ-Proteobacteria(44.2%,含Group-1,-2和-3共3个亚群)、β-Proteobacteria(21.2%)、Rhodobacter-like(7.69%)及2个未知亚群unknown Group-1(21.2%)和Group-2(5.77%)。其中γ-Proteobacteria占到总克隆的44.2%,在低盐的乌梁素海环境中出现高比例的γ-Proteobacteria之前并未见类似报道,并且乌梁素海中存在一些可能是富营养化湖泊特有的AAPB。这表明AAPB可能在富营养化湖泊生态系统的维持和稳定中有重要作用。     

Isolation of Optically Targeted Single Bacteria by Application of Fluidic Force Microscopy to Aerobic Anoxygenic Phototrophs from the Phyllosphere

In their natural environment, bacteria often behave differently than they do under laboratory conditions. To gain insight into the physiology of bacteria in situ, dedicated approaches are required to monitor their adaptations and specific behaviors under environmental conditions. Optical microscopy is crucial for the observation of fundamental characteristics of bacteria, such as cell shape, size, and marker gene expression. Here, fluidic force microscopy (FluidFM) was exploited to isolate optically selected bacteria for subsequent identification and characterization. In this study, bacteriochlorophyll-producing bacteria, which can be visualized due to their characteristic fluorescence in the infrared range, were isolated from leaf washes. Bacterial communities from the phyllosphere were investigated because they harbor genes indicative of aerobic anoxygenic photosynthesis. Our data show that different species of Methylobacterium express their photosystem in planta, and they show a distinct pattern of bacteriochlorophyll production under laboratory conditions that is dependent on supplied carbon sources.     

Influence of Light on Carbon Utilization in Aerobic Anoxygenic Phototrophs

Aerobic anoxygenic phototrophs contain photosynthetic reaction centers composed of bacteriochlorophyll. These organisms are photoheterotrophs, as they require organic carbon substrates for their growth whereas light-derived energy has only an auxiliary function. To establish the contribution of light energy to their metabolism, we grew the phototrophic strain Erythrobacter sp. NAP1 in a carbon-limited chemostat regimen on defined carbon sources (glutamate, pyruvate, acetate, and glucose) under conditions of different light intensities. When grown in a light-dark cycle, these bacteria accumulated 25% to 110% more biomass in terms of carbon than cultures grown in the dark. Cultures grown on glutamate accumulated the most biomass at moderate light intensities of 50 to 150 μmol m⁻² s⁻¹ but were inhibited at higher light intensities. In the case of pyruvate, we did not find any inhibition of growth by high irradiance. The extent of anaplerotic carbon fixation was detemined by radioactive bicarbonate incorporation assays. While the carboxylation activity provided 4% to 11% of the cellular carbon in the pyruvate-grown culture, in the glutamate-grown cells it provided only approximately 1% of the carbon. Additionally, we tested the effect of light on respiration and photosynthetic electron flow. With increasing light intensity, respiration decreased to approximately 25% of its dark value and was replaced by photophosphorylation. The additional energy from light allows the aerobic anoxygenic phototrophs to accumulate the supplied organic carbon which would otherwise be respired. The higher efficiency of organic carbon utilization may provide an important competitive advantage during growth under carbon-limited conditions.     

Occurrence of Hydrogenases in Cyanobacteria and Anoxygenic Photosynthetic Bacteria: Implications for the Phylogenetic Origin of Cyanobacterial and Algal Hydrogenases

Hydrogenases are important enzymes in the energy metabolism of microorganisms. Therefore, they are widespread in prokaryotes. We analyzed the occurrence of hydrogenases in cyanobacteria and deduced a FeFe-hydrogenase in three different heliobacterial strains. This allowed the first phylogenetic analysis of the hydrogenases of all five major groups of photosynthetic bacteria (heliobacteria, green nonsulfur bacteria, green sulfur bacteria, photosynthetic proteobacteria, and cyanobacteria). In the case of both hydrogenases found in cyanobacteria (uptake and bidirectional), the green nonsulfur bacterium Chloroflexus aurantiacus was found to be the closest ancestor. Apart from a close relation between the archaebacterial and the green sulfur bacterial sulfhydrogenase, we could not find any evidence for horizontal gene transfer. Therefore, it would be most parsimonious if a Chloroflexus-like bacterium was the ancestor of Chloroflexus aurantiacus and cyanobacteria. After having transmitted both hydrogenase genes vertically to the different cyanobacterial species, either no, one, or both enzymes were lost, thus producing the current distribution. Our data and the available data from the literature on the occurrence of cyanobacterial hydrogenases show that the cyanobacterial uptake hydrogenase is strictly linked to the occurrence of the nitrogenase. Nevertheless, we did identify a nitrogen-fixing Synechococcus strain without an uptake hydrogenase. Since we could not find genes of a FeFe-hydrogenase in any of the tested cyanobacteria, although strains performing anoxygenic photosynthesis were also included in the analysis, a cyanobacterial origin of the contemporary FeFe-hydrogenase of algal plastids seems unlikely. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Lauren Ancel Meyers]     

Aphotic N2 Fixation in the Eastern Tropical South Pacific Ocean

We examined rates of N₂ fixation from the surface to 2000 m depth in the Eastern Tropical South Pacific (ETSP) during El Niño (2010) and La Niña (2011). Replicated vertical profiles performed under oxygen-free conditions show that N₂ fixation takes place both in euphotic and aphotic waters, with rates reaching 155 to 509 µmol N m⁻² d⁻¹ in 2010 and 24±14 to 118±87 µmol N m⁻² d⁻¹ in 2011. In the aphotic layers, volumetric N₂ fixation rates were relatively low (<1.00 nmol N L⁻¹ d⁻¹), but when integrated over the whole aphotic layer, they accounted for 87–90% of total rates (euphotic+aphotic) for the two cruises. Phylogenetic studies performed in microcosms experiments confirm the presence of diazotrophs in the deep waters of the Oxygen Minimum Zone (OMZ), which were comprised of non-cyanobacterial diazotrophs affiliated with nifH clusters 1K (predominantly comprised of α-proteobacteria), 1G (predominantly comprised of γ-proteobacteria), and 3 (sulfate reducing genera of the δ-proteobacteria and Clostridium spp., Vibrio spp.). Organic and inorganic nutrient addition bioassays revealed that amino acids significantly stimulated N₂ fixation in the core of the OMZ at all stations tested and as did simple carbohydrates at stations located nearest the coast of Peru/Chile. The episodic supply of these substrates from upper layers are hypothesized to explain the observed variability of N₂ fixation in the ETSP.     

Aerobic and Anaerobic Ammonia-Oxidizing Microorganisms in Low-Temperature Hydrothermal Fe-Si-rich Precipitates of the Southwestern Pacific Ocean

Fe-Si-rich hydrothermal precipitates are distributed widely in low-temperature diffusing hydrothermal fields. Due to the significant contribution of Fe-oxidizing bacteria (FeOB) to the formation of this type of hydrothermal precipitates, previous studies focus mostly on investigating FeOB-related microbial populations, albeit these precipitates actually accommodate abundant other microbial communities, particularly those involved in marine nitrogen cycle. In this study, we investigated the composition, diversity, and abundance of aerobic and anaerobic ammonia-oxidizing microorganisms dwelling in low-temperature Fe-Si-rich hydrothermal precipitates of the Lau Integrated Study Site based on ammonia monooxygenase (amoA) gene and 16S rRNA gene. Phylogenetic analysis revealed the common presence of ammonia-oxidizing archaea (AOA), Nitrosospira-like ammonia-oxidizing bacteria (AOB) and anaerobic ammonium-oxidizing anammox (bacteria) in the Fe-Si-rich hydrothermal precipitates. Quantitative PCR analysis showed that AOA dominated the whole microbial community and the abundance of archaeal amoA gene was 2–3 orders of magnitude higher than that of AOB and anammox bacteria. Result of glycerol dialkyl glycerol tetraether analysis confirmed the presence and abundance of AOA. Our results suggest that microbial ammonia oxidations, especially archaeal aerobic ammonia oxidation, are prevalent and pivotal processes in low-temperature diffusing hydrothermal fields.

Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.     

Patterns in Abundance,Cell Size and Pigment Content of Aerobic Anoxygenic Phototrophic Bacteria along Environmental Gradients in Northern Lakes

There is now evidence that aerobic anoxygenic phototrophic (AAP) bacteria are widespread across aquatic systems, yet the factors that determine their abundance and activity are still not well understood, particularly in freshwaters. Here we describe the patterns in AAP abundance, cell size and pigment content across wide environmental gradients in 43 temperate and boreal lakes of Québec. AAP bacterial abundance varied from 1.51 to 5.49 x 10⁵ cells mL^-1, representing <1 to 37% of total bacterial abundance. AAP bacteria were present year-round, including the ice-cover period, but their abundance relative to total bacterial abundance was significantly lower in winter than in summer (2.6% and 7.7%, respectively). AAP bacterial cells were on average two-fold larger than the average bacterial cell size, thus AAP cells made a greater relative contribution to biomass than to abundance. Bacteriochlorophyll a (BChla) concentration varied widely across lakes, and was not related to AAP bacterial abundance, suggesting a large intrinsic variability in the cellular pigment content. Absolute and relative AAP bacterial abundance increased with dissolved organic carbon (DOC), whereas cell-specific BChla content was negatively related to chlorophyll a (Chla). As a result, both the contribution of AAP bacteria to total prokaryotic abundance, and the cell-specific BChla pigment content were positively correlated with the DOC:Chla ratio, both peaking in highly colored, low-chlorophyll lakes. Our results suggest that photoheterotrophy might represent a significant ecological advantage in highly colored, low-chlorophyll lakes, where DOC pool is chemically and structurally more complex.     

Carbon Metabolism of Filamentous Anoxygenic Phototrophic Bacteria of the Family Oscillochloridaceae

The carbon metabolism of representatives of the family Oscillochloridaceae (Oscillochloris trichoides DG6 and the recent isolates Oscillochloris sp. R, KR, and BM) has been studied. Based on data from an inhibitory analysis of autotrophic CO₂ assimilation and measurements of the activities of the enzymes involved in this process, it is concluded that, in all Oscillochloris strains, CO₂ fixation occurs via the operation of the Calvin cycle. Phosphoenolpyruvate (PEP), which is formed in this cycle, can be involved in the metabolism via the following reaction sequence: PEP (+CO₂) å oxalacetate å malate å fumarate å succinate å succinyl-CoA (+CO₂) å 2-oxoglutarate. Acetate, utilized as an additional carbon source, can be carboxylated to pyruvate by pyruvate synthase and further involved in the metabolism via the above reaction sequence. Propionyl-CoA synthase and malonyl-CoA reductase, the key enzymes of the 3-hydroxypropionate cycle, have not been detected in Oscillochloris representatives.__________Translated from Mikrobiologiya, Vol. 74, No. 3, 2005, pp. 305–312.Original Russian Text Copyright © 2005 by Berg, Keppen, Krasil’nikova, Ugol’kova, Ivanovsky.