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The microbial community mediated biogeochemical cycles play important role in global C-cycle and display a sensitive response to environmental changes. Limited information is available on microbial composition and functional diversity controlling biogeochemical cycles in the riverine environment. The Ganga River water and sediment samples were studied for environmental gene tags with reference to carbohydrate metabolism, photoheterotrophy and chemolithotrophy using high throughput shotgun metagenomic sequencing and functional annotation. The diversity of environmental gene tags specific microbial community was annotated against reference sequence database using Kaiju taxonomic classifier. The metagenomic analyses revealed that the river harbored a broad range of carbohydrate and energy metabolism genes. The in-depth investigation of metagenomic data revealed that the enzymes associated with reverse TCA cycle, Calvin-Benson cycle enzyme RuBisCO, starch and sucrose metabolism genes were highly abundant. The enzymes associated with sulfur metabolism such as EC:2.7.7.4 (sulfate to ammonium per sulfate), EC:1.8.1.2, EC:1.8.7.1 (sulfite to H2S) were prevalent in both the class of samples. The principal component analysis of the functional profiles revealed that the water and sediment samples were clustered distinctly suggesting that both the sites had variable abundance of functional genes and associated microbiota. The taxonomic classification showed abundance of Proteobacteria, Actinobacteria and Bacteroidetes phyla. Also, the metagenomic study showed the presence of purple sulfur bacteria viz. Thiodictyon, Nitrosococcus and purple non-sulfur bacteria viz. Bradyrhozobium and Rhodobacter. The study demonstrates that the Ganga River microbiome has prevalence of functional genes involved in carbohydrate anabolism and catabolism, and CO2 fixation with great prospects in cellulose and sulfide degrading enzyme production and characterization.

Lacustrine organic-rich source rocks (shales and mudstones) were examined to assess the depositional environment and organic input sources of the third and fourth members of the Eocene Shahejie Formation, Bohai Bay Basin, China. Major organic contributions to the Shahejie Formation from dinoflagellates, diatoms, Botryococcus and marine pelagophyte/chrysophyte algae were determined using n-alkane distributions, gammacerane index and diagnostic steranes. Traces of higher plant biomarkers suggest that terrigenous organic inputs were limited. The pervasive presence of β-carotane, aryl isoprenoids, paleorenieratane, renieratane, isorenieratane, 2α-methylhopanes and crocetane indicate significant organic contributions from bacterial communities including cyanobacteria, purple sulfur bacteria (Chromatiaceae), green sulfur bacteria (Chlorobiaceae), and sulfate-reducing bacteria. The extent of H2S content, bacterial sulfate reduction, and photic zone euxinia (PZE) were evaluated by determining the aryl isoprenoids ratio (AIR: 0.7–9.0), the presence of isorenieratene derivatives, and the fate of sulfur in the water column. There was a decrease of PZE extent and duration from the northeast to the southwest of the palaeo-lake, and there was a decrease of water body salinity and bottom water anoxia from the fourth to the third member of the Shahejie Formation. Abrupt environmental perturbations in the third member of the Shahejie Formation are indicated not only by significant changes in parameters such as the pristane/phytane and β-carotane/n-C20 alkane ratios, the gammacerane index, the isorenieratane/C18 aryl isoprenoid, and the AIR, but also by the time lag in the expansion of cyanobacterial lineages after the expansion of purple/green sulfur bacteria, as well as seawater incursions. The unexpected occurrence of intact C30 4-desmethylsteranes (24-n-propylcholestanes) in the Shahejie Formation is first reported here, after very careful checking, and provides unambiguous biological evidence for at least two marine transgression events reaching the Eocene Dongying palaeo-lake. The organic enrichment of the petroleum source rocks in the Shahejie Formation is a consequence of combined indigenous lacustrine algal production, the constrained and favourable preservation conditions, and significant bacterial contributions and marine organic matter inputs to the lake.

Traditional methods to combat disease with antimicrobial agents in aquaculture have caused serious concern and alternative approaches using probiotics have been sought. A photosynthetic purple sulfur bacteria Marichromatium purpuratum RuA2 that thrives at salt concentrations of 0.5% to 5.0% and has a more temperate tolerance for oxygen was isolated from a marine fish pond located on the southwestern shore of Qigu, Taiwan. The effects of M. purpuratum RuA2 on the water quality parameters, the occurrence of the sulfonamide resistance gene sul1 and the microbial community were investigated in situ. Supplementation with strain RuA2 resulted in an increased removal rate of total organic carbon and nitrate ions, as well as a lower occurrence of sul1, in the bacterial community. The abundance and diversity of the bacterial community in the control and M. purpuratum RuA2-supplemented water samples were investigated. Proteobacteria, Bacteroidetes, Cyanobacteria, Actinobacteria and Planctomycetes were identified to be the top five predominant phyla in the control and M. purpuratum RuA2-supplemented water samples. However, supplementation with M. purpuratum RuA2 increased the diversity of the bacterial community composition. Fourteen unique genera were detected solely in strain RuA2-supplemented water samples and the relative abundance of seven shared genera was associated with supplementation with strain RuA2. In conclusion, M. purpuratum RuA2 showed a desirable capacity for improving water quality, reducing the occurrence of the resistance gene sul1 and advantageous effects on the microbial community structure. Tolerant to salinity and oxygen, M. purpuratum RuA2 exhibits an attractive potential for resolving the challenges facing aquaculture today.

Spheroidene and spheroidenone from the non-sulfur bacterium Rhodobacter ( Rba. ) sphaeroides were incorporated into diphenylamine (DPA) LH1-RC and LH2 complexes from sulfur bacteria Allochromatium ( Alc. ) minutissimum and Ectothiorhodospira ( Ect. ) haloalkaliphila in which carotenoid (Car) biosynthesis was inhibited by ~ 95%. A series of biochemical characteristics of the modified LH2 complexes was studied (electrophoretic mobility, absorption and CD spectra, Car composition, Car-to-BChl energy transfer and thermal stability). It was found that the electrophoretic mobility of the complexes with incorporated Cars did not change compared to that of the control and DPA-complexes, indicating the absence of any significant change in the structure of LH complexes upon DPA-treatment and subsequent incorporation of Cars. The analysis of fluorescence excitation spectra of the spheroidene-incorporated LH2 complex (LH2:sph) and the spheroidenone-incorporated LH2 complex (LH2:sph-ne) showed that spheroidene and spheroidenone exhibited relatively low efficiencies of energy transfer to BChl, when incorporated into the LH2 DPA-complexes from Alc. minutissimum and Ect. haloalkaliphila , although, they showed high efficiencies, being in their natural state in the LH2 complexes from Rba. sphaeroides . A significant increase in thermostability observed for the LH2:sph and LH2:sph-ne complexes with respect to the LH2 DPA-complexes indicated that the two incorporated Cars stabilized the structure of the LH2 complexes.

There is an ongoing debate around the effect of microaerobic/aerobic conditions on the wastewater treatment performance and stability of enriched purple phototrophic bacteria (PPB) cultures. It is well known that oxygen-induced oxidative conditions inhibit the synthesis of light harvesting complexes, required for photoheterotrophy. However, in applied research, several publications have reported efficient wastewater treatment at high dissolved oxygen (DO) levels. This study evaluated the impact of different DO concentrations (0-0.25 mg·L−1, 0-0.5 mg·L−1 and 0-4.5 mg·L−1) on the COD, nitrogen and phosphorus removal performances, the biomass yields, and the final microbial communities of PPB-enriched cultures, treating real wastewaters (domestic and poultry processing wastewater). The results show that the presence of oxygen suppressed photoheterotrophic growth, which led to a complete pigment and colour loss in a matter of 20-30 h after starting the batch. Under aerobic conditions, chemoheterotrophy was the dominant catabolic pathway, with wastewater treatment performances similar to those achieved in common aerobic reactors, rather than those corresponding to phototrophic systems (i.e. considerable total COD decrease (45-57% aerobically vs. ± 10% anaerobically). This includes faster consumption of COD and nutrients, lower nutrient removal efficiencies (50-58% vs. 72-99% for NH4+-N), lower COD:N:P substrate ratios (100:4.5-5.0:0.4-0.8 vs. 100:6.7-12:0.9-1.2), and lower apparent biomass yields (0.15-0.31 vs. 0.8-1.2 g CODbiomass·g CODremoved−1)). The suppression of photoheterotrophy inevitably resulted in a reduction of the relative PPB abundances in all the aerated tests (below 20% at the end of the tests), as PPB lost their main competitive advantage against competing aerobic heterotrophic microbes. This was explained by the lower aerobic PPB growth rates (2.4 d−1 at 35 °C) when compared to common growth rates for aerobic heterotrophs (6.0 d−1 at 20 °C). Therefore, PPB effectively outcompete other microbes under illuminated-anaerobic conditions, but not under aerobic or even micro-aerobic conditions, as shown by continuously aerated tests controlled at undetectable DO levels. While their aerobic heterotrophic capabilities provide some resilience, at non-sterile conditions PPB cannot dominate when growing chemoheterotrophically, and will be outcompeted.

Coastal-plain paleosols in the 3.0 Ga Farrel Quartzite of Western Australia have organic surface (A horizon) and sulfate-rich subsurface (By) horizons, like soils of the Atacama Desert of Chile, Dry Valleys of Antarctica, and 3.7 Ga paleosols of Mars. Farrel Quartzite paleosols include previously described microfossils, permineralized by silica in a way comparable with the Devonian Rhynie Chert, a well known permineralized Histosol. Five microfossil morphotypes in the Farrel Quartzite include a variety of spheroidal cells (Archaeosphaeroides) as well as distinctive large spindles (new genus provisionally assigned to cf. Eopoikilofusa). Previously published cell-specific carbon isotopic analyses of the Farrel Quartzite microfossils, and unusually abundant sulfate considering a likely anoxic atmosphere, allow interpretation of these morphotypes as a terrestrial community of actinobacteria, purple sulfur bacteria, and methanogenic Archaea.

We examined the distributions of tetrapyrrole pigments (i.e. intact chlorophylls and bacteriochlorophylls, pheopigments) as well as their compound-specific carbon and nitrogen isotopic compositions in the sediments of three Swiss lakes (Lakes Rotsee, Cadagno and Zurich) and the Black Sea to investigate the biogeochemical cycling of carbon and nitrogen mediated by phototrophic eukaryotes (algae) and bacteria. The factors controlling chlorin isotope variations are discussed and the feasibility to use chlorins as indicators for reconstructions of surface water environments is evaluated. Chlorophyll a and its derivatives including pheophytin a, a pheophytin a epimer, pyropheophytin a, 132,173-cyclopheophorbide-a-enol, chlorophyllone a as well as steryl and carotenol chlorin esters were detected in all sediments. The presence of bacteriochlorophylls e and their derivatives confirmed the presence of brown strains of green phototrophic sulfur bacteria (Chlorobiaceae; GSB) in all three lakes. In the shallower Lakes Rotsee and Cadagno, purple sulfur bacteria (Chromatiaceae; PSB) were also present as confirmed by bacteriochlorophyll a derivatives. Despite the different degrees of water column hypoxia at the studied sites, the chlorins in all sediments were attributed to rapid transformation of intact tetrapyrroles and the formation of related pheopigments. The scatter of compound-specific carbon isotopic compositions of Chl a and its derivatives resulted from different timing of pheopigment formation, likely due to the interaction of blooms of various phytoplankton communities at different times of the year and the variable degrees of carbon limitation and/or different contributions of recycled organic matter (OM). The nitrogen isotopic composition of the chloropigments mainly derived from nitrate assimilation in Lake Zurich and the Black Sea, whereas ammonium and nitrate assimilation were predominant in Lake Rotsee. In the epilimnion of the meromictic Lake Cadagno, dissolved organic nitrogen (DON) supplied to the surface water from ammonium assimilation in the chemocline may be the main nitrogen source. Phototrophic sulfur bacteria in Lakes Rotsee and Cadagno thrived mainly under dissolved organic carbon depleted conditions within the chemocline and in the hypolimnion. GSB may use predominantly ammonium and at least in Lake Cadagno also perform N2 fixation. In contrast, the nitrogen source of PSB could not be reconstructed with δ15N values of bacteriochlorins, because nitrogen isotopic fractionation during BChl a synthesis seems to be almost independent of the assimilated substrate.

Mahoney Lake is a permanently anoxic and sulfidic (euxinic) lake that has a dense plate of purple sulfur bacteria positioned at mid-water depth (∼7 m) where free sulfide intercepts the photic zone. We analyzed the isotopic composition of sulfate (δ34SSO4 and δ18OSO4), sulfide (δ34SH2S), and the water (δ18OH2O) to track the potentially coupled processes of dissimilatory sulfate reduction and phototrophic sulfide oxidation within an aquatic environment with extremely high sulfide concentrations (>30 mM). Large isotopic offsets observed between sulfate and sulfide within the monimolimnion (δ34SSO4-H2S = 51‰) and within pore waters along the oxic margin (δ34SSO4-H2S > 50‰) are consistent with sulfate reduction in both the sediments and the anoxic water column. Given the high sulfide concentrations of the lake, sulfur disproportionation is likely inoperable or limited to a very narrow zone in the chemocline, and therefore the large instantaneous fractionations are best explained by the microbial process of sulfate reduction. Pyrite extracted from the sediments reflects the isotopic composition of water column sulfide, suggesting that pyrite buried in the euxinic depocenter of the lake formed in the water column. The offset between sulfate and dissolved sulfide decreases at the chemocline (δ34SSO4-H2S = 37‰), a trend possibly explained by elevated sulfate reduction rates and inconsistent with appreciable disproportionation within this interval. Water column sulfate exhibits a linear response in δ18OSO4–δ34SSO4 and the slope of this relationship suggests relatively high sulfate reduction rates that appear to respond to seasonal changes in the productivity of purple sulfur bacteria. Although photosynthetic activity within the microbial plate influences the δ18OSO4–δ34SSO4 relationship, the biosignature for photosynthetic sulfur bacteria is restricted to the oxic/anoxic transition zone and is apparently minor relative to the more prevalent process of sulfate reduction operative throughout the light-deprived deeper anoxic water column and sediment pore waters.

Modern travertines, carbonate deposits in Ca-rich hydrothermal water with high pCO2, often display a changing environment along the water path, with corresponding variability in the microbial communities. We investigated a travertine-bearing hot spring at the Blue Pool in northern Sumatra, Indonesia. The thermal water of ~ 62 °C with high H2S (200 μM) and pCO2 (~ 1 atm) developed a travertine mound ~ 70 m wide. The concentrations of the gas components H2S and CO2, decrease immediately after the water is discharged, while the dissolved oxygen, pH, and aragonite saturation increase in the downstream direction. Responding to the geochemical gradient in the water, the surface biofilms change color from white to pink, light-green, dark-green, and brown as the water flows from the vent; this corresponds to microbial communities characterized by chemolithoautotrophs (Halothiobacillaceae), purple sulfur bacteria (Chromatiaceae), Anaerolineaceae, and co-occurrence of green non-sulfur bacteria (Chloroflexales)-Cyanobacteria, and green sulfur bacteria (Chlorobiales), respectively. In an environment with a certain level of H2S (> 1 μM), sulfur digestion and anoxygenic photosynthesis can be more profitable than oxygenic photosynthesis by Cyanobacteria. The precipitated carbonate mineral consists of aragonite and calcite, with the proportion of aragonite increasing downstream due to the larger Mg2 +/Ca2 + ratio in the water or the development of thicker biofilm. Where the biofilm is well developed, the aragonite travertines often exhibit laminated structures that were likely associated with the daily metabolism of these bacteria. The microbiological and sedimentological features at the Blue Pool may be the modern analogs of geomicrobiological products in the early Earth. Biofilm of anoxygenic photosynthetic bacteria had the potential to form ancient stromatolites that existed before the appearance of cyanobacteria.

This research aimed to study the diversity of purple nonsulfur bacteria (PNSB) and to investigate the effect of Hg concentrations in shrimp ponds on PNSB diversity. Amplification of the pufM gene was detected in 13 and 10 samples of water and sediment collected from 16 shrimp ponds in Southern Thailand. In addition to PNSB, other anoxygenic phototrophic bacteria (APB) were also observed; purple sulfur bacteria (PSB) and aerobic anoxygenic phototrophic bacteria (AAPB) although most of them could not be identified. Among identified groups; AAPB, PSB and PNSB in the samples of water and sediment were 25.71, 11.43 and 8.57%; and 27.78, 11.11 and 22.22%, respectively. In both sample types, Roseobacter denitrificans (AAPB) was the most dominant species followed by Halorhodospira halophila (PSB). In addition two genera, observed most frequently in the sediment samples were a group of PNSB (Rhodovulum kholense, Rhodospirillum centenum and Rhodobium marinum). The UPGMA dendrograms showed 7 and 6 clustered groups in the water and sediment samples, respectively. There was no relationship between the clustered groups and the total Hg (HgT) concentrations in the water and sediment samples used (

Current H2S treatment methods for sour gases require considerable amounts of chemicals and energy, or in case of biological treatment, unwanted diluents such as oxygen or nitrogen may be introduced. In order to reduce those requirements, the viability of an anaerobic biological H2S removal process using purple phototrophic bacteria (PPB) was investigated in this study. PPB can use sunlight, and centrate as nutrient source, thus potentially reducing energy and chemical requirements. An added benefit is the production of biomass with potential uses, such as single cell protein. An inoculum of PPB enriched from domestic wastewater was grown photoautotrophically with sulfide as the electron donor and inorganic carbon in a mixed culture. Additionally, synthetic medium and centrate as well as high (56 ± 11 Wm-2) and low (27 ± 3 Wm-2) IR irradiation were trialled. Finally, a process model was developed to study biomass specific removal rates and yield. The results showed that a mixed culture of PPB removed sulfide completely in synthetic media (121 ± 9 mg-S.L−1) at a maximum rate of 1.79 ± 0.16 mg-S(Lh)−1 (low irradiance) and 2.9 mg-S(Lh)−1 (high irradiance). The pH increased in both experiments from about 8.5 to 9. Sulfide removal rates using centrate and low irradiance were similar. However Fe and Mn were found to be limiting growth and sulfide removal. In all experiments, Chromatiaceae (purple sulfur bacteria) were most abundant at the end of the experiment, while at the start purple non-sulfur bacteria were most abundant (from the inoculum). Process modelling and experimental work identified the sulfide oxidation to be a multi-step process with accumulation of intermediates. Specific rates were directly dependent on light input, doubling at high irradiance. Sulfide oxidation was estimated at 0.100 ± 0.014 h−1 (0.085 ± 0.012 g-S(g-VS.h)−1) at low irradiance, and the biomass yield at 0.86 ± 0.05 mg-COD.mg-COD−1. This process model enables the virtual evaluation of autotrophic sulfide removal by PPB in a continuous scaled-up process. Overall, the photoautotrophic removal of sulfide seems to be a viable option, especially because of the possibility of using sunlight as an energy source and centrate as a nutrient source.

The greatest mass extinction on Earth occurred 252 million years ago during the latest Permian. Complete biotic recovery, characterized by a return to pre-extinction diversity levels, took an extraordinarily long time (ca. 5 × 10 6 yr), probably because harsh conditions developed repeatedly during the Early Triassic. Here, we show the recurrence of euxinic conditions during the Early Triassic and the development of especially severe such conditions during the late Early Triassic, just prior to full biotic recovery from the mass extinction. Dibenzothiophenes and carotenoids accumulated in upper Lower Triassic sediments from South China, located on the western margin of the Paleotethys Ocean. Among these, chlorobactane, a biomarker for green-pigmented green sulfur bacteria, and okenane, a biomarker for purple sulfur photosynthetic bacteria, were identified in upper Early Triassic samples. Both compounds were detected in limestone (micrite) and we therefore infer that planktonic green and purple sulfur bacteria were the sources of these carotenoids, and that their presence indicates photic zone euxinia at the time of deposition. Concentrations of redox sensitive elements (M, V, and U), relative to that of Al, and the U/Th ratio, progressively increased during the late Early Triassic. The euxinic conditions represented by the carotenoids and the elements were likely caused by a combination of locally shallow restricted conditions and global environmental oscillations, such as those related to global warming, during the late Early Triassic. The presence of these biomarkers, together with the increase in the abundance of redox sensitive elements relative to Al and the U/Th, suggests that euxinic conditions could be one of the causes for the delayed recovery of marine communities in the Paleotethys Ocean after the latest Permian mass extinction event.

Lake Cadagno is characterised by a compact chemocline with high concentrations of purple sulfur bacteria (PSB). 2D-DIGE was used to monitor the global changes in the proteome of Candidatus "Thiodictyon syntrophicum" strain Cad16T both in the presence and absence of light. This study aimed to disclose details regarding the dark CO2 assimilation of the PSB, as this mechanism is often observed but is not yet sufficiently understood. Our results showed the presence of 17 protein spots that were more abundant in the dark, including three enzymes that could be part of the autotrophic dicarboxylate/4-hydroxybutyrate cycle, normally observed in archaea.

Purple sulfur phototrophic bacteria accumulate various storage materials, such as sulfur globules, glycogen or polyhydroxy alkanoates (PHAs) under appropriate conditions. The formation of these materials requires reducing power which might be recovered upon their breakdown. This work aims at the understanding of the metabolism of PHA and its link to the nitrogenase mediated in vivo H 2 evolution in Thiocapsa roseopersicina BBS. The strain could accumulate 30% of the dry cell weight in the form of PHAs. Analysis of the genome sequence revealed the loci involved in PHAs synthesis and degradation. Phylogenetic analysis indicated independent evolution of the anabolic and catabolic proteins. A mutant carrying deleted PHA biosynthesis genes has been created in a host containing nitrogenase but none of the hydrogenases. Determination of the H 2 evolving capacity of the mutant revealed significantly reduced H 2 production in PHA deficient cells. Addition of excess electron sources such as thiosulfate stimulated the H 2 production via multiple effects.

Okenone is a unique ketocarotenoid found in many purple sulfur bacteria; it is important because of its unique light absorption and photoprotection properties. Okenane, a compound formed by diagenetic reduction of okenone, is an important biomarker in geochemical analyses of sedimentary rocks. Despite its ecological and biogeochemical importance, the biochemical pathway for okenone synthesis has not yet been fully described. The genome sequence of an okenone-producing organism, Thiodictyon sp. strain CAD16, revealed four genes whose predicted proteins had strong sequence similarity to enzymes known to produce ψ-end group modifications of carotenoids in proteobacteria. These four genes encoded homologs of a 1,2-carotenoid hydratase (CrtC), an O-methyltransferase (CrtF), and two paralogs of carotenoid 3,4-desaturases (CrtD). Expression studies in lycopene- or neurosporene-producing strains of Escherichia coli confirmed the functions of crtC and crtF, but the crtD paralogs encoded enzymes with previously undescribed functions. One enzyme, CruS, was only distantly related to CrtD desaturases, was bifunctional, and performed a 3,4-desaturation and introduced a C-2 keto group into neurosporene derivatives in the presence of dioxygen. The enzyme encoded by the other crtD paralog also represents a new enzyme in carotenogenesis and was named cruO. CruO encodes the C-4/4' ketolase uniquely required for okenone biosynthesis. The identification of CruO and the demonstration of its biochemical activity complete the elucidation of the biosynthetic pathway for okenone and other related ketocarotenoids.

Carbonates of the 1640 million years (Ma) old Barney Creek Formation (BCF), McArthur Basin, Australia, contain more than 22 different C40 carotenoid derivatives including lycopane, γ-carotane, β-carotane, chlorobactane, isorenieratane, β-isorenieratane, renieratane, β-renierapurpurane, renierapurpurane and the monoaromatic carotenoid okenane. These biomarkers extend the geological record of carotenoid derivatives by more than 1000 million years. Okenane is potentially derived from the red-colored aromatic carotenoid okenone. Based on a detailed review of the ecology and physiology of all extant species that are known to contain okenone, we interpret fossil okenane as a biomarker for planktonic purple sulfur bacteria of the family Chromatiaceae. Okenane is strictly a biomarker for anoxic and sulfidic conditions in the presence of light (photic zone euxinia) and indicates an anoxic/oxic transition (temporarily) located at less than 25 m depth and, with a high probability, less than 12 m depth. For the BCF, we also interpret renierapurpurane, renieratane and β-renierapurpurane as biomarkers for Chromatiaceae with a possible contribution of cyanobacterial synechoxanthin to the renierapurpurane pool. Although isorenieratane may, in principle, be derived from actinobacteria, in the BCF these biomarkers almost certainly derive from sulfide-oxidizing phototrophic green sulfur bacteria (Chlorobiaceae). Biological precursors of γ-carotane, β-carotane and lycopane are found among numerous autotrophic and almost all phototrophic organisms in the three domains of life. In the BCF, a paucity of diagnostic eukaryotic steroids suggests that algae were rare and, therefore, that cyanobacterial carotenoids such as β-carotene, echinenone, canthaxanthin and zeaxanthin are the most likely source of observed β-carotane. γ-Carotane may be derived from cyanobacteria, Chlorobiaceae and green non-sulfur bacteria (Chloroflexi), while the most likely biological sources for lycopane in the BCF are carotenoids of the lycopene, rhodopin and spirilloxanthin series abundant in purple sulfur bacteria.

Summary A 991 bp DNA fragment, consisting of a 225 amino acid reading frame homologous to outer membrane protein coding ompA gene, was cloned from a purple sulfur bacterium Allochromatium vinosum. The homology analysis revealed up to 51% similarity to other bacterial species. The absence of branching within diazotrophs or other taxonomically related groups shows the structural importance of the protein regardless of the metabolism and evolution of the species.

Molecular and stable carbon isotope compositions of source-specific hydrocarbons have been used to reconstruct palaeoenvironmental conditions during deposition of the Middle Hettangian to Upper Sinemurian sediments on the northern epicontinental Tethys margin, Frick Swiss Jura. Increasing algal, cyanobacterial and phytoplanktonic (i.e., dinoflagellate) contributions associated with the 13 C-enrichment of cyanobacteria derivatives (i.e., hopanes and monomethylalkanes) suggest enhanced primary productivity upsection. This is related to the 13 C-enrichment of dissolved CO 2 in the upper layers and the progressive increase of depth and oxygenation of the water column. In the Middle Hettangian shallow-water environments (lagoon), the occurrence of green sulfur bacteria ( Chlorobiaceae ) derivatives indicates that the lower part of the water column was strictly anoxic and rich in H 2 S. Since these bacteria require very low light intensity to grow, these euxinic conditions may be extended up to the photic zone, allowing for anaerobic photosynthesis. Light penetration depth is most likely reduced by high productivity and/or turbidity in the photic zone. In these sediments, 13 C-depleted hopanoids (−39.5‰) are most likely associated with phototrophic purple sulfur bacteria utilizing isotopically light organic carbon at the base of the aerobic zone. These purple sulfur bacteria may have consumed the H 2 S used by Chlorobiaceae in the deeper layers and thus, sustained the algae and cyanobacteria productivity in the upper layers. The 13 C-depleted carbonate (−13.3‰) may be partially related to the anaerobic oxidation of the organic matter during bacterial sulfate-reduction.

Lipids extracted from sediments in a saline seep in the Salt Basin of Lancaster County, Nebraska included alkanes, alkenes, alkanols, phytol, C27–30 sterols, C30–32 hopanoids, tetrahymanol, glycolipid and phospholipid fatty acids, and lipopolysaccharide hydroxyl fatty acids. Biomarker profiles suggest that the brine seeps of Salt Basin support a microbial ecosystem adapted to a relatively highly saline and sulfidic environment. The phospholipid fatty acid (PLFA) and lipopolysaccharide hydroxyl fatty acid profiles are consistent with the presence of large numbers of sulfate-reducing bacteria (SRB) in black, sulfidic muds surrounding the seeps. In the context of field and laboratory observations, the presence of large amounts of glycolipid fatty acids is attributed to large populations of photosynthetic microorganisms (cyanobacteria, phytoplankton, and purple sulfur bacteria) that likely play important roles in the local cycling of carbon and sulfur. The sterol profile and the detection of polyunsaturated alkenes (C21:6 ,C 21:7 ,C 30:4, and C30:5) implicates microalgae as important contributors of organic matter at the site. Comparatively high concentrations of phytol (58.2 l gg � 1 dry wt sediment) record the activity of photosynthetic organisms in the system. The d 13 C of phytol (� 37.1&) is compatible with a dominance of microalgae, cyanobacteria, or higher plants and a lesser contribution from phototrophic sulfur bacteria. The presence of various intermediate degradation products of phytol (phytenes and phytadienes) indicates that SRB likely mediate the chemical reduction of phytol in the anaerobic zone. The presence of C30–32 hopanols can be attributed to cyanobacteria and methanotrophs in oxic regions of the water column, whereas bacterivorous ciliates and phototrophic sulfur bacteria living at the chemocline are likely sources of tetrahymanol. The carbon isotopic composition of individual fatty acids and neutral lipids helps to identify source organisms. These microorganisms and others constitute a unique and integrated ecosystem prescribed by the geochemistry of the Salt Basin.

An unusual purple sulfur bacterium present in the pink layer of the Ebro Delta microbial mats has been identified through the study of its ultrastructural features. As pure cultures of this bacterium have not been obtained, due to its inability to grow in axenic conditions, only enrichment cultures where it reached at least 90% of total biomass have been considered. In enrichment cultures, the cells are rods that are 5.4+/-0.6 microm wide and 11.0+/-2.1 microm long. The color of the cell suspensions is pink to pinkish-red. Cells are motile by means of a polar tuft of flagella and multiply by binary fission. This bacterium possesses an extensive internal photosynthetic membrane system consisting of stacks of lamellae, contains bacteriochlorophyll a and carotenoids of normal spirilloxanthin series and deposits sulfur intracellularly. In natural samples, the most abundant phototrophic purple sulfur bacterium developing in this ecosystem has the same kind of intracytoplasmic membrane system, but the cells differ slightly in size and arrangement, in that they are ovoid, 4.2+/-0.5 microm wide and 6.0+/-1.4 microm long, and can be seen forming irregular non-motile clumps which are embedded in slime. Differences observed between field samples and enrichment cultures suggest that environmental conditions may bring about changes in the phenotypic characteristics of the cells. The morphological characteristics of the described bacterium resemble those of large Chromatia. However, this bacterium differs from known species in this group, particularly in terms of its photosynthetic membrane system and in its light absorption properties.

Visible light-induced degradation processes were studied in vitro in senescent cells of two purple sulfur bacteria (Thiohalocapsa halophila and Halochromatium salexigens) isolated from microbial mats from Camargue (France). These reactions act on the phytyl side chain of bacteriochlorophyll-a and on palmitoleic and cis-vaccenic acids. The experiments also confirmed some previous results, i.e. the regiospecific enzymatic oxygenation of the allylic carbon 10 of cis-vaccenic acid in senescent cells of T. halophila. The subsequent detection of substantial amounts of photoproducts from the phytyl chain and mono-unsaturated fatty acids in the lipid extracts of the microbial mats from which these two strains were isolated clearly established the importance of photodegradation processes in this particular ecosystem. The presence of photoproducts of cis-vaccenic acid showed that under natural conditions photochemical reactions act extensively on senescent phototrophic bacteria. Significant amounts of 10-oxooctadecanoic and 10-hydroxy-11-oxooctadecanoic acids were also detected in the lipid extracts. The detection of these compounds, which result from the enzymatic oxidation of carbon 10 of cis-vaccenic acid, supports a strong T. halophila contribution to the microbial mats.

This report covers the analyses of tetrapyrrole pigments in sediments and numerous source biota from northern central Florida Bay. Sediment cores were all carbonate marls and ‘bedrock’ (Pleistocene limestones) was typically at 0.6–1.2 m bsf. (below sea floor). Extraction of the sediments was performed using tetrahydrofuran, shown to be 3–7 times as effective as more common solvents. Surficial sediments were found to contain a pigment distribution indicating a diatomaceous-cyanobacterial biofilm/mat underlain with purple sulfur bacteria as the microphytobenthos. Downhole trends in pigment diagenesis revealed differences due to paleoenvironment. That is, when bacteriochlorophyll-a (BCHLa) plus derivatives were elevated, indicating strong syn-depositional anoxia, the pheophytins-a (PTINsa) were the major chlorophyll-a (CHLa) derivatives. Conversely, when BCHL-a plus derivatives were low, indicating oxic to dys-oxic syn-depositional conditions, then pyropheophorbide-a (pPBIDa) and 132, 172-cyclopheophorbide-a (CYCLO) were strongly dominant. The generation of cyclopheophorbide in carbonate marls with weakly anoxic to dysoxic syn-depositional conditions may yield an oil-source paleoenvironmental marker for bitumen containing compounds such as bicycloalkanoporphyrins (BiCAPs). Downhole conversions were observed for the following diagenetic steps; CHLa to pheophytin-a (PTINa), PTINa to pyropheophytin-a (pPTINa), pPBIDa to CYCLO, BCHLa to bacteriopheophytin-a (BPTINa), and BPTINa to bacteriopyropheophytin-a (BpPTINa).

Stable carbon isotopic analysis was performed on sedimentary biomarkers of a shallow sulfide-rich monomictic lake, Lake Ciso (NE Spain). Specific biomarkers derived from phototrophic sulfur bacteria in Lake Ciso were considerably depleted in 13C, most likely due to the depleted 13C-content of the dissolved inorganic carbon that was photosynthetically fixed. Recycling of respired CO2, a well-known phenomenon in monomictic lakes, probably caused this depletion. The stable carbon isotopic composition of terrestrial markers, such as C25–33 odd-carbon-numbered n-alkanes and C22–30 even-carbon-numbered n-alkan-1-ols and fatty acids, were rather similar to each other and their 13C depleted values (c. −31 to −35‰) indicated that they were derived from the surrounding vegetation. Phytol was predominantly derived from the bacteriochlorophylls of phototrophic purple sulfur bacteria as were specific fatty acids.

Energy transfer between antenna complexes was studied by means of time resolved absorption spectroscopy in the purple sulfur bacteria Chromatium tepidum and C. vinosum. The first species contains only one peripheral antenna complex, B800-B50, the other one has two, B800-850 and B800-820. Results obtained with chromatophores of C. tepidum indicated two time constants for energy transfer from B800-850 to the core complex, of 10 ps and a smaller one of 30 ps, suggesting non-uniform distances between the peripheral and core complexes. Similar results were obtained with C. vinosum, where time constants of 7 and 30 ps were found. Energy transfer from B800-820 to B800-850 was significantly faster. These results show that the rates of energy transfer from bacteriochlorophyll 850 to the core complex in the purple sulfur bacteria studied are quite similar to those found in purple non-sulfur bacteria. This may seem remarkable in view of the fact that the core antenna in C. tepidum absorbs at the unusually long wavelength of 918 nm, but a calculation indicates that the overlap integral for energy transfer to the core is not dramatically less than in C. vinosum.

Energy trapping in chromatophores of the purple sulfur bacteria Chromatium vinosum and Chromatium tepidum has been examined by means of picosecond transient absorption spectroscopy. In C. vinosum, time constants for excitation quenching in the core antenna by open and closed reaction centres were 50 and 230 ps, respectively. In C. tepidum, excitation quenching by closed reaction centres occurred with a single time constant of 310 ps. With open reaction centres, the kinetics of decay of excitations in the core antenna were more complicated. The decay was multi-exponential, with a major contribution from a 140 ps component and minor contributions from 40 ps and 530 ps components. By comparison with the kinetics of oxidation of the primary donor, the 140 ps component was identified as being due to excitation trapping by open reaction centres. This trapping time is slow as compared with other purple bacteria, and is most likely a consequence of the red-shift of the core antenna with respect to the reaction centre. The origin of the 40 ps component is not entirely clear, but it probably represents energy transfer to the reaction centre as well. The 530 ps component may reflect a fraction of bacteriochlorophyll a that transfers its energy to the reaction centre very inefficiently, or not at all. In C. vinosum as well as in C. tepidum, no kinetic components were found that could be associated with internal core antenna relaxation, which implies that equilibration within the core antenna occurred within our time resolution of 10–15 ps.

The first molecular biology study on the purple sulfur photosynthetic bacterium Thiocapsa roseopersicina is reported, namely, the construction of cosmid libraries and isolation of a hydrogenase gene cluster by hybridization with hydrogenase structural genes from the purple non-sulfur bacterium, Rhodobacter capsulatus. The sequenced gene cluster contains six open reading frames, the products of which show significant degrees of identity (from 40 to 78%) with hydrogenase gene products necessary for biosynthesis of the group-I of [NiFe]hydrogenases. The structural hupSLC genes encode the small and large hydrogenase subunits and a hydrophobic protein shown to accept electrons from hydrogenase in R. capsulatus. They are followed downstream by three genes, hupDHI, which are similar to hydrogenase accessory genes found in other bacteria.

Microbial mats characteristically are dominated by a few functional groups of microbes: cyanobacteria, colorless sulfur bacteria, purple sulfur bacteria, and sulfate-reducing bacteria. Their combined metabolic activities result in steep environmental microgradients, particularly of oxygen and sulfide.The driving force of most microbial mats is photosynthesis by cyanobacteria and algae. Subsequently, sulfate-reducing bacteria, using excretion-, lysis-, and decomposition products of cyanobacteria, produce sulfide by the dissimilatory reduction of sulfate. The sulfide can be reoxidized to sulfate by colorless and purple sulfur bacteria.Colorless sulfur bacteria are chemotrophic organisms primarily oxidizing sulfide and other reduced forms of sulfur with oxygen to obtain energy. The oxidation of reduced sulfur species also provides reducing equivalents for the reduction of carbon dioxide to cellular carbon. The final product of sulfide oxidation is sulfate, with elemental sulfur, deposited extracellularly, as the principal intermediate.Purple sulfur bacteria primarily are anaerobic phototrophic organisms using sulfide and other reduced forms of sulfur exclusively as the electron donor for the reduction of CO2 to cellular carbon. Usually, sulfur is temporarily stored intracellularly. The final product of the oxidation of reduced forms of sulfur is sulfate.The niches for these metabolically different groups of microbes in ecosystems with steep, often non-overlapping, gradients of oxygen and sulfide appear to be spatially separated. However, maximum viable counts of colorless sulfur bacteria and purple sulfur bacteria were both found in the top 5-10 mm of mats. Unexpectedly, viable counts of sulfate-reducing bacteria also peaked at the same depth horizon.Sulfide is inhibitory for most oxygenic phototrophs. Sulfide production immediately underneath the layer of cyanobacteria might inhibit their growth, and, consequently, that of the entire ecosystem. In microbial mats this effect is minimized by the combined action of colorless and purple sulfur bacteria. Colorless sulfur bacteria generally have a much higher affinity for sulfide than purple sulfur bacteria, however, in microbial mats, their activity is hampered by low oxygen supply rates. As shown by pure culture studies with colorless sulfur bacteria, sulfide is incompletely oxidized when oxygen is short in supply, resulting in the production of potential electron donors for purple sulfur bacteria, such as sulfur, thiosulfate and polysulfides. In the absence of purple sulfur bacteria, colorless sulfur bacteria would not be able to maintain a low sulfide concentration due to shortage of oxygen, which in turn would result in increased inhibition of oxygenic photosynthesis.It thus appears that the combined action of all four groups of functional microbes mentioned effectively results in optimal growth of these recent ''stromatolites''.

Summary Results of 16S ribosomal RNA cataloguing demonstrate the lack of close relationship between Bacteroides amylophilus ATCC 29744 and other members of the genus Bacteroides. B. amylophilus shows a remote relationship to purple sulfur bacteria and their non-phototrophic relatives (gamma subdivision, as defined by Woese et al., 1984b), while genuine members of Bacteroides cluster separately, forming one of the phylogenetically ancient groups of eubacteria. This finding is in accord with differences found between the chemotaxonomic properties of B. amylophilus and other Bacteroides species tested. On the basis of these results we propose that B. amylophilus be transferred to a new genus, Ruminobacter , as Ruminobacter amylophilus (Hamlin and Hungate 1956) comb. nov.

Growth characteristics and treatment capacity of a mixed population of Chromatiaceae (purple sulfur bacteria) were determined using settled, sieved swine waste as a growth medium. The bacteria were cultured in Erlenmeyer flasks under incandescent illumination at a temperature of 26°C. They survived ephemeral sulfide concentrations of up to 528 mg liter −1 , while growing well at continuous sulfide concentrations of 7–28 mg liter −1 . Optimum pH was 7–8 and optimum waste solids concentration was 0·9%. Specific growth rates ranged up to 0·75 day −1 and averaged 0·4–0·5 day −1 . Bacteriochlorophyll a yields reached 40 mg liter −1 . Soluble BOD 5 and soluble COD were reduced by 92% and 70%, respectively, over a period of 12 days in waste-grown Chromatiaceae cultures. Ammonia-nitrogen and soluble phosphorus were reduced by 30% and 49%, respectively, over the same period of time. Protein yield was 1·8 g liter −1 .

Methods based on paper and cellulose column chromatography are described for the rapid separation of small quantities of bacteriochlorophyll and Chlorobium chlorophyll. Spectral absorption curves are given as evidence of the efficiency of the methods to separate pure products. Curves are given for bacteriochlorophyll in ethyl ether and in ethanol. It was found that bacteriochlorophyll could be stored at −10 ° without much deterioration, but it was necessary to saturate the solvents with H 2 S to prevent decomposition of the chlorophyll during purification. Chlorobium chlorophyll has very different chromatographic properties from chlorophyll a, but similar spectroscopic properties. The chlorophyll in the purple sulfur bacteria and that in the green sulfur bacteria were shown to be different pigments.