Syntrophic anaerobic photosynthesis via direct interspecies electron transfer.

Microbial phototrophs, key primary producers on Earth, use H2O, H2, H2S and other reduced inorganic compounds as electron donors. Here we describe a form of metabolism linking anoxygenic photosynthesis to anaerobic respiration that we call 'syntrophic anaerobic photosynthesis'. We show that photoautotrophy in the green sulfur bacterium Prosthecochloris aestaurii can be driven by either electrons from a solid electrode or acetate oxidation via direct interspecies electron transfer from a heterotrophic partner bacterium, Geobacter sulfurreducens. Photosynthetic growth of P. aestuarii using reductant provided by either an electrode or syntrophy is robust and light-dependent. In contrast, P. aestuarii does not grow in co-culture with a G. sulfurreducens mutant lacking a trans-outer membrane porin-cytochrome protein complex required for direct intercellular electron transfer. Syntrophic anaerobic photosynthesis is therefore a carbon cycling process that could take place in anoxic environments. This process could be exploited for biotechnological applications, such as waste treatment and bioenergy production, using engineered phototrophic microbial communities.

In situ high-resolution structure of the baseplate antenna complex in Chlorobaculum tepidum.

Photosynthetic antenna systems enable organisms harvesting light and transfer the energy to the photosynthetic reaction centre, where the conversion to chemical energy takes place. One of the most complex antenna systems, the chlorosome, found in the photosynthetic green sulfur bacterium Chlorobaculum (Cba.) tepidum contains a baseplate, which is a scaffolding super-structure, formed by the protein CsmA and bacteriochlorophyll a. Here we present the first high-resolution structure of the CsmA baseplate using intact fully functional, light-harvesting organelles from Cba. tepidum, following a hybrid approach combining five complementary methods: solid-state NMR spectroscopy, cryo-electron microscopy, isotropic and anisotropic circular dichroism and linear dichroism. The structure calculation was facilitated through development of new software, GASyCS for efficient geometry optimization of highly symmetric oligomeric structures. We show that the baseplate is composed of rods of repeated dimers of the strongly amphipathic CsmA with pigments sandwiched within the dimer at the hydrophobic side of the helix.

Succession Processes in the Anoxygenic Phototrophic Bacterial Community in Lake Kislo-Sladkoe (Kandalaksha Bay, White Sea).

The community of anoxygenic phototrophic bacteria (APB) in the water column of Lake Kislo- Sladkoe (Kandalaksha Bay, White Sea), which has recently become separated from the sea, was investigated in March-April 2012, March-April 2013, and in September 2013. The lake, which was previously considered meromictic, was in fact mixed and was strongly affected by the sea. In winter the lake is sometimes washed off with seawater, and this together with the seasonal cycles of succession processes determines the succession of the community. The consequences of the mixing in autumn 2011 could be observed in the APB community as late as autumn 2013. Green-colored green sulfur bacteria (GSB) usually predominated in the chemocline. In winter 2013 stagnation resulted in turbidity of water under the ice, which was responsible for both predom- inance of the brown GS B forms and the changes ratio of the species of purple sulfur bacteria (PS B) in anoxic water layers. Production of anoxygenic photosynthesis in the lake was at least 240 mg C m-2 day-- in September and 0-20 mg C m-2 day- in March-April, which corresponded to 40 and 69%, respectively, of oxygenic photosynthesis. Okenone-containing purple sulfur bacteria, strain TcakPS12 were isolated in 2012 from lake water. The ells of this strain form filaments of not separated cells. Strain TcakPS12 exhibited 98% similarity with the type strains of Thiocapsapendens DSM.236 and Thiocapsa bogorovii BBS, as well as with the strains AmPS10 and TcyrPS 10, which were isolated from Lake Kislo-Sladkoe in 2010.

The ultrastructure of Chlorobaculum tepidum revealed by cryo-electron tomography.

Chlorobaculum (Cba) tepidum is a green sulfur bacterium that oxidizes sulfide, elemental sulfur, and thiosulfate for photosynthetic growth. As other anoxygenic green photosynthetic bacteria, Cba tepidum synthesizes bacteriochlorophylls for the assembly of a large light-harvesting antenna structure, the chlorosome. Chlorosomes are sac-like structures that are connected to the reaction centers in the cytoplasmic membrane through the BChl α-containing Fenna-Matthews-Olson protein. Most components of the photosynthetic machinery are known on a biophysical level, however, the structural integration of light harvesting with charge separation is still not fully understood. Despite over two decades of research, gaps in our understanding of cellular architecture exist. Here we present an in-depth analysis of the cellular architecture of the thermophilic photosynthetic green sulfur bacterium of Cba tepidum by cryo-electron tomography. We examined whole hydrated cells grown under different electron donor conditions. Our results reveal the distribution of chlorosomes in 3D in an unperturbed cell, connecting elements between chlorosomes and the cytoplasmic membrane and the distribution of reaction centers in the cytoplasmic membrane.

Characterization of Melioribacter roseus gen. nov., sp. nov., a novel facultatively anaerobic thermophilic cellulolytic bacterium from the class Ignavibacteria, and a proposal of a novel bacterial phylum Ignavibacteriae.

A novel moderately thermophilic, facultatively anaerobic chemoorganotrophic bacterium strain P3M-2(T) was isolated from a microbial mat developing on the wooden surface of a chute under the flow of hot water (46°C) coming out of a 2775-m-deep oil exploration well (Tomsk region, Russia). Strain P3M-2(T) is a moderate thermophile and facultative anaerobe growing on mono-, di- or polysaccharides by aerobic respiration, fermentation or by reducing diverse electron acceptors [nitrite, Fe(III), As(V)]. Its closest cultivated relative (90.8% rRNA gene sequence identity) is Ignavibacterium album, the only chemoorganotrophic member of the phylum Chlorobi. New genus and species Melioribacter roseus are proposed for isolate P3M-2(T) . Together with I. album, the new organism represents the class Ignavibacteria assigned to the phylum Chlorobi. The revealed group includes a variety of uncultured environmental clones, the 16S rRNA gene sequences of some of which have been previously attributed to the candidate division ZB1. Phylogenetic analysis of M. roseus and I. album based on their 23S rRNA and RecA sequences confirmed that these two organisms could represent an even deeper, phylum-level lineage. Hence, we propose a new phylum Ignavibacteriae within the Bacteroidetes-Chlorobi group with a sole class Ignavibacteria, two families Ignavibacteriaceae and Melioribacteraceae and two species I. album and M. roseus. This proposal correlates with chemotaxonomic data and phenotypic differences of both organisms from other cultured representatives of Chlorobi. The most essential differences, supported by the analyses of complete genomes of both organisms, are motility, facultatively anaerobic and obligately organotrophic mode of life, the absence of chlorosomes and the apparent inability to grow phototrophically.

Structural variability in wild-type and bchQ bchR mutant chlorosomes of the green sulfur bacterium Chlorobaculum tepidum.

The self-aggregated state of bacteriochlorophyll (BChl) c molecules in chlorosomes belonging to a bchQ bchR mutant of the green sulfur bacteria Chlorobaculum tepidum, which mostly produces a single 17(2)-farnesyl-(R)-[8-ethyl,12-methyl]BChl c homologue, was characterized by solid-state nuclear magnetic resonance (NMR) spectroscopy and high-resolution electron microscopy. A nearly complete (1)H and (13)C chemical shift assignment was obtained from well-resolved homonuclear (13)C-(13)C and heteronuclear (1)H-(13)C NMR data sets collected from (13)C-enriched chlorosome preparations. Pronounced doubling (1:1) of specific (13)C and (1)H resonances revealed the presence of two distinct and nonequivalent BChl c components, attributed to all syn- and all anti-coordinated parallel stacks, depending on the rotation of the macrocycle with respect to the 3(1)-methyl group. Steric hindrance from the 20-methyl functionality induces structural differences between the syn and anti forms. A weak but significant and reproducible reflection at 1/0.69 nm(-1) in the direction perpendicular to the curvature of cylindrical segments observed with electron microscopy also suggests parallel stacking of BChl c molecules, though the observed lamellar spacing of 2.4 nm suggests weaker packing than for wild-type chlorosomes. We propose that relaxation of the pseudosymmetry observed for the wild type and a related BChl d mutant leads to extended domains of alternating syn and anti stacks in the bchQ bchR chlorosomes. Domains can be joined to form cylinders by helical syn-anti transition trajectories. The phase separation in domains on the cylindrical surface represents a basic mechanism for establishing suprastructural heterogeneity in an otherwise uniform supramolecular scaffolding framework that is well-ordered at the molecular level.

Prosthecochloris indica sp. nov., a novel green sulfur bacterium from a marine aquaculture pond, Kakinada, India.

A green sulfur bacterium, strain JAGS6T was isolated from a marine aquaculture pond located near Kakinada on the east coast of India. Cells of strain JAGS6T were Gram-negative, non-motile, coccoid, 1-1.2 microm in diameter, with prosthecae. Phylogenetic analysis on the basis of 16S rRNA gene sequences showed that strain JAGS6T clusters with members of the genus Prosthecochloris and the sequence similarity with the nearest relative, Prosthecochloris vibrioformis, is 96.7%. Cultures of strain JAGS6T are green in color and the cells contain bacteriochlorophyll c and most likely carotenoids of the chlorobactene series as photosynthetic pigments. Strain JAGS6T is mesophilic, halotolerant (up to 7% NaCl) and is obligately phototrophic, utilizing sulfide but not thiosulfate as a photosynthetic electron donor. Sulfur globules are deposited outside the cells during oxidation of sulfide. On the basis of 16S rRNA gene sequence analysis and its morphological and physiological characteristics, strain JAGS6T is distinct from described species of the genus Prosthecochloris and we propose to describe it as a new species, Prosthecochloris indica, sp. nov. The type strain is JAGS6T (=JCM 13299T=ATCC BAA1214T).

Chlorobaculum tepidum regulates chlorosome structure and function in response to temperature and electron donor availability.

Green sulfur bacteria (GSB) rely on the chlorosome, a light-harvesting apparatus comprised almost entirely of self-organizing arrays of bacteriochlorophyll (BChl) molecules, to harvest light energy and pass it to the reaction center. In Chlorobaculum tepidum, over 97% of the total BChl is made up of a mixture of four BChl c homologs in the chlorosome that differ in the number and identity of alkyl side chains attached to the chlorin ring. C. tepidum has been reported to vary the distribution of BChl c homologs with growth light intensity, with the highest degree of BChl c alkylation observed under low-light conditions. Here, we provide evidence that this functional response at the level of the chlorosome can be induced not only by light intensity, but also by temperature and a mutation that prevents phototrophic thiosulfate oxidation. Furthermore, we show that in conjunction with these functional adjustments, the fraction of cellular volume occupied by chlorosomes was altered in response to environmental conditions that perturb the balance between energy absorbed by the light-harvesting apparatus and energy utilized by downstream metabolic reactions.

Physiology of phototrophic iron(II)-oxidizing bacteria: implications for modern and ancient environments.

Phototrophic iron(II) [Fe(II)]-oxidizing bacteria are present in modern environments and evidence suggests that this metabolism was present already on early earth. We determined Fe(II) oxidation rates depending on pH, temperature, light intensity, and Fe(II) concentration for three phylogenetically different phototrophic Fe(II)-oxidizing strains (purple nonsulfur bacterium Rhodobacter ferrooxidans sp. strain SW2, purple sulfur bacterium Thiodictyon sp. strain F4, and green sulfur bacterium Chlorobium ferrooxidans strain KoFox). While we found the overall highest Fe(II) oxidation rates with strain F4 (4.5 mmol L(-1) day(-1), 800 lux, 20 degrees C), the lowest light saturation values [at which maximum Fe(II) oxidation occurred] were determined for strain KoFox with light saturation already below 50 lux. The oxidation rate per cell was determined for R. ferrooxidans strain SW2 to be 32 pmol Fe(II) h(-1) per cell. No significant toxic effect of Fe(II) was observed at Fe(II) concentrations of up to 30 mM. All three strains are mesophiles with upper temperature limits of c. 30 degrees C. The main pigments were identified to be spheroidene, spheroidenone, OH-spheroidenone (SW2), rhodopinal (F4), and chlorobactene (KoFox). This study will improve our ecophysiological understanding of iron cycling in modern environments and will help to evaluate whether phototrophic iron oxidizers may have contributed to the formation of Fe(III) on early earth.

Diversity of anoxygenic phototrophic sulfur bacteria in the microbial mats of the Ebro Delta: a combined morphological and molecular approach.

The diversity of purple and green sulfur bacteria in the multilayered sediments of the Ebro Delta was investigated. Specific oligonucleotide primers for these groups were used for the selective amplification of 16S rRNA gene sequences. Subsequently, amplification products were separated by denaturing gradient gel electrophoresis and sequenced, which yielded a total of 32 sequences. Six of the sequences were related to different cultivated members of the green sulfur bacteria assemblage, whereas seven fell into the cluster of marine or halophilic Chromatiaceae. Six sequences were clustered with the family Ectothiorhodospiraceae, three of the six being closely related to chemotrophic bacteria grouped together with Halorhodospira genus, and the other three forming a group related to the genus Ectothiorhodospira. The last thirteen sequences constituted a cluster where no molecular isolate from microbial mats has so far been reported. Our results indicate that the natural diversity in the ecosystem studied has been significantly underestimated in the past and point out the presence of novel species not related to all known purple sulfur bacteria. Furthermore, the detection of green sulfur bacteria, after only an initial step of enrichment, suggests that -- with the appropriate methodology -- several genera, such as Prosthecochloris, could be established as regular members of marine microbial mats.

Chlorobium tepidum mutant lacking bacteriochlorophyll c made by inactivation of the bchK gene, encoding bacteriochlorophyll c synthase.

The gene encoding bacteriochlorophyll (BChl) c synthase was identified by insertional inactivation in the photosynthetic green sulfur bacterium Chlorobium tepidum and was named bchK. The bchK mutant of C. tepidum was rusty-orange in color and completely lacked BChl c. Because of the absence of the BChl c antenna, the mutant grew about seven times slower than the wild type at light intensities that were limiting to the wild type (< 90 micromol m(-2) s(-1)). Various pheophorbides, which probably represent precursors of BChl c which had lost magnesium, accumulated in the mutant cells. A small fraction of these pheophorbides were apparently esterified by the remaining chlorophyll (Chl) a and BChl a synthases in cells. The amounts of BChl a, Chl a, isoprenoid quinones, carotenoids, Fenna-Matthews-Olson protein, and chlorosome envelope protein CsmA were not significantly altered on a cellular basis in the mutant compared to in the wild type. This suggests that the BChl a antennae, photosynthetic reaction centers, and remaining chlorosome components were essentially unaffected in the mutant. Electron microscopy of thin sections revealed that the mutant lacked normal chlorosomes. However, a fraction containing vestigial chlorosomes, denoted "carotenosomes," was partly purified by density centrifugation; these structures contained carotenoids, isoprenoid quinones, and a 798-nm-absorbing BChl a species that is probably protein associated. Because of the absence of the strong BChl c absorption found in the wild type, the bchK mutant should prove valuable for future analyses of the photosynthetic reaction center and of the roles of BChl a in photosynthesis in green bacteria. An evolutionary implication of our findings is that the photosynthetic ancestor of green sulfur bacteria could have evolved without chlorosomes and BChl c and instead used only BChl a-containing proteins as the major light-harvesting antennae.

Roseiflexus castenholzii gen. nov., sp. nov., a thermophilic, filamentous, photosynthetic bacterium that lacks chlorosomes.

A novel thermophilic, photosynthetic bacterium, designated strain HLO8T, was isolated from a bacterial mat in a Japanese hot spring. Morphologically, the isolate was an unbranched multicellular filament with a cell diameter of 0.8-1.0 microm. The bacterium was red to reddish-brown in colour and formed a distinct red bacterial mat in the natural environment. It was able to grow photoheterotrophically under anaerobic light conditions and also chemoheterotrophically under aerobic dark conditions. Optimal growth occurred at 50 degrees C and pH 7.5-8.0. The cells contained bacteriochlorophyll (Bchl) a and gamma-carotene derivatives as photosynthetic pigments, but lacked Bchl c and chlorosomes. Cellular fatty acids in the isolate were mainly C16:0, C14:0 and C15:0. The major quinone was menaquinone-11. The DNA G+C content was 62.0 mol% (by HPLC). Phylogenetic analysis based on 16S rDNA sequencing suggested that the isolate belonged to the anoxygenic filamentous phototrophic bacteria represented by Chloroflexus aurantiacus, but was clearly distant from all members in this group (the sequence similarities between the isolate and its relatives were less than 83.8%). Based on genotypic and phenotypic data, the name Roseiflexus castenholzii gen. nov., sp. nov. is proposed for this isolate; the type strain is HLO8T (= DSM 13941T = JCM 11240T).

Light responses in the green sulfur bacterium Prosthecochloris aestuarii: changes in prosthecae length, ultrastructure, and antenna pigment composition.

The morphology (mainly prosthecae length), ultrastructure, and antenna pigment composition of the green sulfur bacterium Prosthecochloris aestuarii changed when grown under different light intensities. At light intensities of 0.5 and 5 micromol quanta m(-2) s(-1), the cells had a star-like morphology. Prosthecae, the characteristic appendages of the genus Prosthecochloris, were 232 nm and 194 nm long, respectively. In contrast, when grown at 100 micromol quanta m(-2) s(-1), these appendages were shorter (98 nm) and the cells appeared more rod-shaped. Transmission electron microscopy revealed a significant decrease in the cell perimeter to area ratio and in the number of chlorosomes per linear microm of membrane as light intensity increased. In addition to these morphological and ultrastructural responses, Prosthecochloris aestuarii exhibited changes in its pigment composition as a function of light regime. Lower specific pigment content and synthesis rates were found in cultures grown at light intensities above 5 micromol quanta m(-2) s(-1). A blue shift in the bacteriochlorophyll (BChl) c Q(y) absorption maximum of up to 17.5 nm was observed under saturating light conditions (100 micromol quanta m(-2) s(-1)). This displacement was accompanied by changes in the composition of BChl c homologs and by a very low carotenoid content. The morphological, ultrastructural and functional changes exhibited by Prosthecochloris aestuarii revealed the strong light-response capacity of this bacterium to both high and low photon-flux densities.

Effect of carotenoid deficiency on cells and chlorosomes of Chlorobium phaeobacteroides.

The effects of inhibition of carotenoid biosynthesis by 2-hydroxybiphenyl on the photosynthetic growth, pigment composition and chlorosome structure of Chlorobium phaeobacteroides strain CL1401 were examined. At a concentration of 20 micrograms 2-hydroxybiphenyl .ml-1, carotenoid synthesis was largely inhibited (85%), but the photosynthetic growth rate was almost unaffected (mu control = 0.00525 +/- 0.00007 h-1 and mu HBP-treated = 0.00505 +/- 0.0005 h-1). Cells grown in the presence of the inhibitor were 5 microns-70 microns long, while control cells were between 2-5 microns long. Moreover, 2-hydroxybiphenyl-treated cells contained fewer, unevenly distributed chlorosomes per micron of cytoplasmic membrane with an irregular arrangement (2.5 +/- 1.5 vs of 9.1 +/- 1.9). This was concomitant to the 83% decrease in the content of bacteriochlorophyll (BChl) e in 2-hydroxybiphenyl-treated cells. Electron microscopy revealed that the shape of carotenoid-depleted chlorosomes changed from ellipsoidal to spherical, although the mean volume was similar to that of control chlorosomes. SDS-PAGE analysis of the chlorosome polypeptide composition showed that the amount of CsmA protein decreased by 60% in carotenoid-depleted chlorosomes. This was paralleled by a decrease in the baseplate BChl a content. The data suggest that carotenoids are close to the chlorosomal baseplate, where they carry out both structural and photoprotective functions.

Quenching of bacteriochlorophyll fluorescence in chlorosomes from Chloroflexus aurantiacus by exogenous quinones.

The quenching of bacteriochlorophyll (BChl) c fluorescence in chlorosomes isolated from Chloroflexus aurantiacus was examined by the addition of various benzoquinones, naphthoquinones (NQ), and anthraquinones (AQ). Many quinones showed strong quenching in the micromolar or submicromolar range. The number of quinone molecules bound to the chlorosomes was estimated to be as small as one quinone molecule per 50 BChl c molecules. Quinones which exhibit a high quenching effect have sufficient hydrophobicity and one or more hydroxyl groups in the alpha positions of NQ and AQ. Chlorobiumquinone has been suggested to be essential for the endogenous quenching of chlorosome fluorescence in Chlorobium tepidum under oxic conditions. We suggest that the quenching effect of chlorobiumquinone in chlorosomes from Chl. tepidum is related to the 1'-oxo group neighboring the dicarbonyl group.

Functioning of oligomeric-type light-harvesting antenna.

In our previous work, we developed, for the first time, a theory of excitation energy transfer within an oligomeric-type light-harvesting antenna and, in particular, within the chlorosome of green bacteria (Biophys.J., 1996, vol.71, pp.995-1010). The theory was recently developed for a new original exciton model of aggregation of chlorosomal pigments, bacteriochlorophylls (BCh1) c/d/e (Biochem, Mol.Biol.Int., 1996, vol.40, No.2, pp. 243-252). In this paper, it was demonstrated with picosecond fluorescence spectroscopy that this theory explains the antenna-size-dependent kinetics of fluorescence decay in chlorosomal antenna, measured for intact cells of different cultures of the green bacterium Chlorobium limicola with different chlorosomal antenna size determined by electron microscopic examination of the ultrathin sections of the cells. According to our model, the energy transfer dynamics within the chlorosome imply the formation of a cylindrical exciton, delocalized over a tubular aggregate of BCh1 c chains, and inductive-resonance-type transfer of such a cylindrical exciton between the nearest tubular BCh1 c aggregates and to BCh1 a of the chlorosome.

Excitation energy transfer in chlorosomes of green bacteria: theoretical and experimental studies.

A theory of excitation energy transfer within the chlorosomal antennae of green bacteria has been developed for an exciton model of aggregation of bacteriochlorophyll (BChl) c (d or e). This model of six exciton-coupled BChl chains with low packing density, approximating that in vivo, and interchain distances of approximately 2 nm was generated to yield the key spectral features found in natural antennae, i.e., the exciton level structure revealed by spectral hole burning experiments and polarization of all the levels parallel to the long axis of the chlorosome. With picosecond fluorescence spectroscopy it was demonstrated that the theory explains the antenna-size-dependent kinetics of fluorescence decay in chlorosomal antenna, measured for intact cells of different cultures of the green bacterium C. aurantiacus, with different chlorosomal antenna size determined by electron microscopic examination of the ultrathin sections of the cells. The data suggest a possible mechanism of excitation energy transfer within the chlorosome that implies the formation of a cylindrical exciton, delocalized over a tubular aggregate of BChl c chains, and Forster-type transfer of such a cylindrical exciton between the nearest tubular BChl c aggregates as well as to BChl a of the baseplate.

Ultrafast energy transfer in chlorosomes from the green photosynthetic bacterium Chloroflexus aurantiacus.

Energy transfers between the bacteriochlorophyll c and a antennae in light-harvesting chlorosomes from the green bacterium Chloroflexes aurantiacus have been studied in two-color pump-probe experiments with improved sensitivity and wavelength versatility. The BChl c --> BChl a energy transfers are well simulated with biexponential kinetics, with lifetimes of 2-3 and 11 ps. They do not exhibit an appreciable subpicosecond component. In the context of a kinetic model for chlorosomes, these lifetimes suggest that both internal BChl c processes and the BChl c --> BChl a energy-transfer step contribute materially to the empirical rod-to-baseplate energy-transfer kinetics.

The microbial community at Laguna Figueroa, Baja California Mexico: from miles to microns.

Laguna Figueroa is a lagoonal complex on the Pacific coast of the Baja California penisula 200 km south of the Mexican-United States border. The hypersaline lagoon is 16 km long and 2-3 km wide with a salt marsh and evaporite flat and is separated from the ocean by a barrier dune and beach. At the salt marsh-evaporite flat interface a stratified microbial community dominated by Microcoleus chthonoplastes is depositing laminated sediments. Similar stratiform deposits with associated microbial mat communities have been found in cherts of the Fig Tree Group, South Africa which are 3.4 GE in age. Heavy rains in the winters of 1978-1979 and 1979-1980 flooded the evaporite flat with 1-3 meters of meteoric water and buried the laminated sediment under 5-10 cm of siliciclastic and clay sediment. These flooding events had a dramatic effect on the composition of the mat community. The Microcoleus dominated community, with species of Chloroflexus sp. and an Ectothiorhodospira-like filamentous purple phototroph, disappeared leaving a community dominated by the purple phototrophs Chromatium sp. and Thiocapsa sp. Recolonization of the surface by species of the cyanobacteria Oscillatoria sp. and Spirulina sp. preceded the return of the Microcoleus community. Field conditions were monitored by ground based observations and supplemented with LandSat and Skylab imagery. The microbial community was studied with light microscopy and transmission electron microscopy. The change in dominating microbial species was correlated with the episodes of flooding.

Chloroherpeton thalassium gen. nov. et spec. nov., a non-filamentous, flexing and gliding green sulfur bacterium.

A flexing and gliding green sulfur bacterium has been isolated from marine sources off the North East coast of the USA. Chloroherpeton thalassium is an obligate phototroph, and requires CO2 and S2 for growth; some organic acids can contribute to cell carbon, and N2 may be fixed. The cells contain typical chlorosomes, and gas vesicles may be present. Bacteriochlorophyll c is the main light harvesting pigment, and a small quantity of bacteriochlorophyll a is also present. Over 80% of the carotenoid is gamma-carotene. DNA base composition of the isolates ranges from 45.0-48.2 mol% G + C.