Phototrophic Sulfur Bacteria Research Articles

Sedimentary pigments in 308 alpine lakes and their relation to environmental gradients

We undertook a comprehensive comparison between the pigment composition of surface sediment samples and contemporary catchment and limnological data deriving from 308 mountain lakes in 11 mountain regions (Lake Districts) covering a wide latitudinal and longitudinal gradient across Europe. This paper examines whether photosynthetic algal and bacterial pigments stored in the lake sediment can be used to identify different lake typologies and population dynamics of primary producers. We focus on a multivariate numerical analysis relating the relative abundance of marker pigments of algae, cyanobacteria and phototrophic sulphur bacteria to a set of physical and chemical factors (both natural and anthropogenic) determining the environmental conditions in mountain lakes. Redundancy Analysis (RDA), including partial RDA, of carotenoid assemblages constrained by environmental variables suggests that the main differences between lake districts are caused by geographic position (e.g. longitude), catchment characteristics (e.g. % carbonate rocks) and chemical variables (e.g. Mg, NO3). Other variables such as temperature and phosphorus play a minor role, probably be cau se of the short length of the gradient covered by these cold and mostly oligotrophic lakes. Pigment composition varies primarily in response to catchment geology and pollution (i.e. acidification from long range transport) gradients. Purple sulphur photosynthetic bacteria (okenone) and cyanobacteria (echinenone, canthaxanthin, scytonemin) are replaced by siliceous algae (fucoxanthin and diatoxanthin), cryptophytes (alloxanthin) and dinoflagellates (diadinoxanthin). With respect to site classification, the pigment ordination shows a clear distinction between the more pristine lakes (in the Pyrenees) and the more polluted sites (in the Tatra Mountains and Central Southern Alps) or those with water higher in solute content (the Julian Alps and Greenland).

Utilization of 'elemental' sulfur by different phototrophic sulfur bacteria (Chromatiaceae, Ectothiorhodospiraceae): A sulfur K-edge XANES spectroscopy study

Phototrophic sulfur bacteria are generally able to use elemental sulfur as an electron donor for anoxygenic photosynthesis. Elemental sulfur is mainly a mixture of cyclo-octasulfur and polymeric sulfur. The purple sulfur bacterium Allochromatium vinosum strongly prefers the polymeric sulfur fraction showing that sulfur speciation has a strong influence on availability of elemental sulfur. X-ray absorption near edge structure (XANES) spectroscopy was used to investigate whether polymeric sulfur is also the preferred sulfur species in other purple sulfur bacteria belonging to the families Chromatiaceae and Ecothiorodospiraceae. The cultures were fed with 50 mM of elemental sulfur consisting of 68% polymeric sulfur and 30% cyclo-octasulfur. In all cultures, elemental sulfur was converted into intra- or extracellular sulfur globules, respectively, and further oxidized to sulfate. Sulfate concentrations were determined by HPLC and turbidometric assays, respectively. However, the added elemental sulfur was only partly used by the bacteria, one part of the 'elemental sulfur' remained in the cultures and was not taken up. XANES spectroscopy revealed that only the polymeric sulfur fraction was taken up by all cultures investigated. This strongly indicates that polymeric 'chain-like' sulfur is the form preferably used by phototrophic sulfur bacteria.

The speciation of soluble sulphur compounds in bacterial culture fluids by X‐ray absorption near edge structure spectroscopy

Over the last decade X‐ray absorption near edge structure (XANES) spectroscopy has been used in an increasing number of microbiological studies. In addition to other applications it has served as a valuable tool for the investigation of the sulphur globules deposited intra‐ or extracellularly by certain photo‐ and chemotrophic sulphur‐oxidizing (Sox) bacteria. For XANES measurements, these deposits can easily be concentrated by filtration or sedimentation through centrifugation. However, during oxidative metabolism of reduced sulphur compounds, such as sulphide or thiosulphate, sulphur deposits are not the only intermediates formed. Soluble intermediates such as sulphite may also be produced and released into the medium. In this study, we explored the potential of XANES spectroscopy for the detection and speciation of sulphur compounds in culture supernatants of the phototrophic purple sulphur bacterium Allochromatium vinosum. More specifically, we investigated A. vinosum ΔsoxY, a strain with an in frame deletion of the soxY gene. This gene encodes an essential component of the thiosulphate‐oxidizing Sox enzyme complex. Improved sample preparation techniques developed for the ΔsoxY strain allowed for the first time not only the qualitative but also the quantitative analysis of bacterial culture supernatants by XANES spectroscopy. The results thus obtained verified and supplemented conventional HPLC analysis of soluble sulphur compounds. Sulphite and also oxidized organic sulphur compounds were shown by XANES spectroscopy to be present, some of which were not seen when standard HPLC protocols were used.

Primary production in Lake La Cruz (Spain) over the last four centuries: reconstruction based on sedimentary signal of photosynthetic pigments

We analysed photosynthetic pigments in annually laminated sediment of meromictic Lake La Cruz, Spain, to cope with the timing and characterisation of primary productivity changes over the last four centuries. The photosynthetic pigments identified included chlorophyll a and b (and its derivatives) and specific carotenoids of different algal groups, such as zeaxanthin, lutein, alloxanthin, diadinoxanthin and diatoxanthin among others. Marker pigments of phototrophic sulfur bacteria were also observed, including bacteriochlorophyll a derivatives, homologue series of bacteriophaeophytins d and bacterial carotenoids okenone and chlorobactene. We investigated the diagenetic processes of pigment alteration in anoxic sediments and the possible implications for paleoproductivity reconstruction and interpretation. The lack of systematic down-core changes in diagenetic indicators suggests that variability of sedimentary pigment concentrations is the result of changes in lake productivity. The lower concentration of algal photosynthetic pigments in the bottom of sediment sequence corresponds to the onset of meromictic conditions. Before that, sediment was not continuously anoxic and the preservation of pigments was reduced. Regarding photosynthetic bacteria, green sulfur bacteria derivatives indicate that population growth was limited until the settled organic matter was sufficient to provide enough sulphide. Moreover, the presence of bacterioviridine, an oxidised derivative of bacteriochlorophyll a, suggest the competitive relation among photosynthetic bacteria. The high relative abundance of zeaxanthin indicates the dominance of picocyanobacteria in the primary productivity over the last centuries. Fluctuations of the pigment signal observed in the sediment sequence during the meromictic period were well correlated with fluctuations of solar activity.

Possible causes for a negative shift in the stable carbon isotope ratio before, during and after the end-Permian mass extinction in Meishan, South China

A 2–4‰ negative shift of δ13C has been reported from many Permian/Triassic (P/Tr) boundary sections around the world. Our carbon isotopic measurements of bulk carbonate and organic matter from the Meishan section, South China show that a –3‰ shift of δ13C spanned ∼30 ka over the end-Permian mass extinction. Carbon isotopic excursions (δ13Ccarb, δ13Corg) coupled with Δ13C (=δ13Ccarb–δ13Corg), marine kerogen %, 87Sr/86Sr of siliciclastics and total organic carbon show geochemical signals underwent six geochemical variation zones (GVZ) over the P/Tr transition. Of these, GVZ 1 corresponds to the lower–middle parts of Bed 24e-1, GVZ 2 to the upper part of Bed 24e-1, GVZ 3 to Beds 24e-2, 24e-3, 25-2 and 25-2, GVZ 4 to Bed 25-3, GVZ 5 to Bed 26, and GVZ 6 to Beds 27–29. A −1‰ shift of δ13C within ∼13 ka before the main extinction was probably generated by possible dissociation of methane hydrate by warming. Subsequent mixing of anoxic stratified ocean led to another −1‰ shift of δ13C within ∼5 ka during the extinction. The −1‰ shift of δ13C within ∼13 ka after the main extinction has probably resulted from massive denudation of soil and sediments caused by the collapse of forests and possible dissociation of methane hydrate at the end of the Permian. Furthermore, a dramatic drop of Δ13C values from 29–30‰ in Bed 24e-3 to 25‰ in Bed 25 indicates an abrupt proliferation of phototrophic sulfur bacteria immediately after the main episode of the end-Permian mass extinction. The Δ13C value increases to 29–30‰ in Bed 26 again, and this is probably due to massive denudation of soil and sediment caused by the collapse of forests between 0 and 27 ka after the main extinction, as revealed by negative shift of δ13C. Low Δ13C value recorded in Beds 27–29 indicates that phototrophic sulfur bacteria may have thrived again and lasted more than 150 ka after the main extinction in the low-latitude Paleo-Tethys.

Predation impact of ciliated and flagellated protozoa during a summer bloom of brown sulfur bacteria in a meromictic coastal lake

Anaerobic phagotrophic protozoa may play an important role in the carbon flux of chemically stratified environments, especially when phototrophic sulfur bacteria account for a high proportion of the primary production. To test this assumption, we investigated the vertical and temporal distribution of microbial heterotrophs and of autotrophic picoplankton throughout the water column of the meromictic coastal lake Faro (Sicily, Italy), in the summer of 2004, coinciding with a bloom of brown-colored green sulfur bacteria. We also assessed the grazing impact of ciliated and flagellated protozoa within the sulfur bacteria plate using a modification of the fluorescently labeled bacteria uptake approach, attempting to minimize the biases intrinsic to the technique and to preserve the in situ anoxic conditions. Significant correlations were observed between ciliate biomass and bacteriochlorophyll e concentration, and between heterotrophic nanoflagellate biomass and chlorophyll a concentration in the water column. The major predators of anaerobic picoplankton were pleuronematine ciliates and cryptomonad flagellates, with clearances of 26.6 and 9.5 nL per cell h(-1), respectively, and a cumulative impact on the picoplankton gross growth rate ranging between 36% and 72%. We concluded that protozoan grazing channels a large proportion of anaerobic picoplankton production to higher trophic levels without restraining photosynthetic bacteria productivity.

Fine scale analysis of shifts in bacterial community structure in the chemocline of meromictic Lake Cadagno, Switzerland

Phototrophic sulfur bacteria in the chemocline of Lake Cadagno, Switzerland, were dominated by purple sulfur bacteria before 1998, but their composition shifted after a presumed disturbance to consist of mainly green sulfur bacteria. This study focused on comparative analyses of the distribution of the green sulfur compared to the purple sulfur bacteria by analyzing specific populations along fine scale depth profiles of the chemocline of Lake Cadagno. Water samples were collected from the chemocline on October 14th, 1998, and on September 28th, 2004. A detailed analysis of chemocline depth profiles revealed that total biomass of phototrophic sulfur bacteria was three times higher in 2004 than in 1998. The three-fold increase of biomass was entirely due to increments in abundance of one population of green sulfur bacteria, identified as Chlorobium clathratiforme. Abundance of purple sulfur bacteria remained unchanged with respect to overall numbers in the chemocline, but also with respect to distribution of different populations in depth in the chemocline. Aggregates of small-celled purple sulfur bacteria decreased in size about four-fold, but remained associated with sulfate-reducing bacteria of the genus Desulfocapsa. Compared to 1998, these had increased in numbers about three times in 2004, resulting in about ten times higher numbers per aggregate. These results demonstrate long-term effects of a presumed disturbance in autumn 1999 and 2000, on environmental conditions and on green sulfur and sulfate-reducing bacteria in the chemocline, however, without changes in the abundance and in the distribution of purple sulfur bacteria.

Вплив деяких важких металів на фотосинтезувальні сіркобактерії Lamprocystis sp.

The growth of phototrophic sulfur bacteria Lamprocystis sp. under the influence of 0.5, 1.0, 1.5, 2.0 and 2.5 mM of CdSO 4 , ZnSO 4 , Pb(NO 3 ) 2 and CuSO 4 was investigated. The control medium did not contain metal salt. The highest inhibition of growth was caused by CuSO 4 , and Pb(NO 3 ) 2 had weaker effect. These salts at the concentration 0.5 mM and higher have decreased the biomass accumulation for 85 and 58% respectively. Addition of CdSO 4 or ZnSO 4 caused the decrease of biomass accumulation only at high salts concentrations in the medium. The qualitative and quantitative composition of the main photosynthetic pigments in the cells at these conditions was determined. Addition of salts of heavy metals to the growth medium of Lamprocystis sp. decreased the pigments content in the cells, and inhibited culture growth. Key words : Cadmium, Zinc, Lead, Copper, sulfur bacteria, bacteriochlorophylles, carotenoides.

The microbial domes of Wadi Muqshin pools, Sultanate of Oman

The paper reports studies on benthic microbial dome‐shaped mats found in hypersaline desert pools in Wadi Muqshin, southern Oman, and details the hydrogeological conditions of the pools, including water quality and recharge features. The upper 1 cm layers of these microbial mats are dominated by cyanobacteria, a phototrophic purple sulphur bacterium and diatoms. The dominant cyanobacterium is Microcoleus chthonoplastes and the purple layer below the upper layer is dominated by the photosynthetic sulphur bacterium Chromatium okenii. It is unusual to find standing water containing microbial domes in such a hyper‐arid, inland site which borders the Rub’ Al Khali (Empty Quarter). The flooding regime here depends largely on ‘fossil’ groundwater (Zone C, L.UER aquifer) mostly derived from the Pleistocene. Attempts to carry out desert agriculture with abstraction of this ‘fossil’ groundwater might cause the extinction of the Muqshin pools.

Carbon isotopic evidence for chemocline upward excursions during the end-Permian event

A negative shift in marine inorganic carbon-isotope composition ( δ 13C carb) during the end-Permian mass extinction has been used as evidence for several different extinction mechanisms. Changes to the δ 13C of organic matter and the difference between it and δ 13C carb (Δ 13C = δ 13C carb − δ 13C org) have been examined at few locations, with conflicting interpretations. We examine the changes to both organic and inorganic carbon isotopes across the Permian–Triassic boundary at two marine sections from South China (Meishan and Shangsi) and compare these to data from other previously published sections. Through these analyses, we demonstrate that a decrease in Δ 13C occurred during the extinction event throughout the Paleo-Tethys ocean. The extent and intensity of the decrease varies by location averaging a negative shift of ∼ 5‰. Several possibilities as to the cause of this shift exist including Siberian trap volcanism, a change in the terrestrial/marine organic carbon input to the system, or a change in the dominant marine biota brought about through environmental changes (such as widespread ocean anoxia/euxinia). The decrease in Δ 13C observed at many of these sections across the event horizon is here interpreted to represent a shift from algae/cyanobacteria to less fractionating phototrophic sulfur bacteria in marine shelf environments resulting from upward excursions of the chemocline. These chemocline upward excursions would release euxinic water to the photic zone allowing phototrophic sulfur bacteria to thrive. The limited available biomarker data are consistent with this interpretation.

Selective enrichment of green sulfur bacteria in the presence of 4-aminobenzenesulfonate (sulfanilate)

A novel selective enrichment method is described for phototrophic green sulfur bacteria even in the presence of purple sulfur and purple nonsulfur bacteria using sulfanilate, which was discovered during efforts to selectively isolate sulfanilate-metabolizing anoxygenic phototrophic bacteria from marine habitats. Samples for these experiments were obtained from beaches, saltpans, subsurface mangrove soils, fish and prawn aquaculture ponds and backwaters of the East and West coasts of India. Photoorganoheterotrophic and photolithoautotrophic enrichments in the absence of sulfanilate predominantly yielded purple bacterial enrichments. In contrast, photolithoautotrophic enrichments in the presence of sulfanilate yielded green-colored enrichments from the same samples. Whole cell absorption spectra of the enrichment cultures revealed the presence of bacteriochlorophyll c and thus green phototrophic bacteria. Microscopic observation demonstrated the presence of sulfur globules outside the bacterial cells and the presence of non-motile cells, some of which had prosthecae. 16S rDNA sequences obtained from green sulfur bacterial strains isolated from enrichment cultures confirmed the presence of representatives of the green sulfur bacterial genera Prosthecochloris and Chlorobaculum. The selective pressure of sulfanilate exerted through inhibition of phototrophic purple sulfur bacteria was demonstrated by inhibition studies using the purple sulfur bacteria Marichromatium indicum JA100 and Marichromatium sp. JA120 (JCM 13533) and the green sulfur bacterium Prosthecochloris sp. JAGS6 (JCM 13299).

Importance of the DsrMKJOP complex for sulfur oxidation in Allochromatium vinosum and phylogenetic analysis of related complexes in other prokaryotes

In the phototrophic sulfur bacterium Allochromatium vinosum, sulfur of oxidation state zero stored in intracellular sulfur globules is an obligate intermediate during the oxidation of sulfide and thiosulfate. The proteins encoded in the dissimilatory sulfite reductase (dsr) locus are essential for the oxidation of the stored sulfur. DsrMKJOP form a membrane-spanning complex proposed to accept electrons from or to deliver electrons to cytoplasmic sulfur-oxidizing proteins. In frame deletion mutagenesis showed that each individual of the complex-encoding genes is an absolute requirement for the oxidation of the stored sulfur in Alc. vinosum. Complementation of the DeltadsrJ mutant using the conjugative broad host range plasmid pBBR1-MCS2 and the dsr promoter was successful. The importance of the DsrMKJOP complex is underlined by the fact that the respective genes occur in all currently sequenced genomes of sulfur-forming bacteria such as Thiobacillus denitrificans and Chlorobaculum tepidum. Furthermore, closely related genes are present in the genomes of sulfate- and sulfite-reducing prokaryotes. A phylogenetic analysis showed that most dsr genes from sulfide oxidizers are clearly separated of those from sulfate reducers. Surprisingly, the dsrMKJOP genes of the Chlorobiaceae all cluster together with those of the sulfate/sulfite-reducing prokaryotes, indicating a lateral gene transfer at the base of the Chlorobiaceae.

Biomarker analysis of microbial diversity in sediments of a saline groundwater seep of Salt Basin, Nebraska

Lipids extracted from sediments in a saline seep in the Salt Basin of Lancaster County, Nebraska included alkanes, alkenes, alkanols, phytol, C 27–30 sterols, C 30–32 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 (C 21:6, C 21:7, C 30:4, and C 30:5) implicates microalgae as important contributors of organic matter at the site. Comparatively high concentrations of phytol (58.2 μg g −1 dry wt sediment) record the activity of photosynthetic organisms in the system. The δ 13C 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 C 30–32 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.

Multi-proxy Reconstruction of Trophic State, Hypolimnetic Anoxia and Phototrophic Sulphur Bacteria Abundance in a Dimictic Lake in Northern Germany over the past 80 Years

During monthly investigations from 1996 to 2000, a hypolimnetic layer of phototrophic sulphur bacteria (Chromatium spp.) were observed in Lake Dudinghausen, a small dimictic lake in northern Germany. This paleolimnological study was initiated to detect if the occurrence of sulphur bacteria was related to cultural eutrophication or reflected natural conditions. Therefore, diatoms, algal pigments, okenone, geochemical proxies, and 210Pb and 137Cs were used in four sediment cores to investigate historical changes in trophic development, hypolimnetic redox conditions, anoxia and phototrophic sulphur bacteria abundances. Fossil diatoms, pigments, the ratio of chlorophyll derivatives to total carotenoids and the ratio of chlorophyll a to its derivatives suggest two phases of eutrophication coupled with hypolimnetic anoxia over the last ~80 years: a first phase from about 1923–1932 and a second from 1952 to 1982. In the first phase the ratios of Fe–Mn as well as Fe–Ca increased, suggesting seasonal anoxia. However, hypolimnetic anoxia was only weak because low levels of okenone suggest no mass development of sulphur bacteria. In contrast, sulphur bacteria increased during the early stages of the second eutrophication phase, suggesting increased temporal and spatial hypolimnetic anoxia. Surprisingly, the ratios of Fe–Mn as well as Fe–Ca decreased during this time. Possibly Fe, Mn and Ca were equally reduced through the intense anoxia. In the final stage, sulphur bacteria decreased again. As these bacteria need both anoxic conditions and a certain amount of light, the increased nutrient load probably led to low Secchi depth and therefore insufficient light conditions. In more recent years, diatoms and pigments suggest a decrease in nutrient levels. A second mass development of sulphur bacteria occurred, probably due to improved light conditions and continued anoxia in the upper hypolimnion. We conclude that the recent development of phototrophic sulphur bacteria do not represent natural conditions in Lake Dudinghausen. Furthermore, the upper sediments contain a completely new diatom flora that never occurred in older sediments of Lake Dudinghausen. Therefore, nutrient levels may eventually reach natural conditions, however they may not represent biological background reference conditions.

Distribution of bacteriochlorophyll homologs in natural populations of brown-colored phototrophic sulfur bacteria

The relative content of the four main bacteriochlorophyll (BChl) e homologs of several populations of brown-colored photosynthetic sulfur bacteria grown in different waterbodies have been measured by high performance liquid chromatography and statistically compared by principal component analysis. All the studied populations possessed representative pigment patterns enriched in highly alkylated bacteriochlorophyll e homologs, with average contents of 0.02±0.01%, 24.92±1.01%, 35.2±0.70%, and 39.9±0.71% for bacteriochlorophyll e1, e2, e3, and e4, respectively. These values clearly differ from those obtained for the same species growing under optimal conditions in laboratory batch cultures (4.99±1.11%, 50.34±1.73%, 28.99±0.63%, and 15.6±1.10% for bacteriochlorophyll e1, e2, e3, and e4, respectively). Multivariate statistical analyses grouped samples into two main clusters, both related to the developmental state of the population. Within these clusters, samples were arranged in several groups according to the physiological pigment response of bacterial populations to light limitation. Although bacteriochlorophyll homolog distribution cannot be considered a real taxonomic character, the data presented demonstrate that it can be useful in field studies since it reflects both the physiological status of the cells and the light regime under which the population has been growing.

Mechanistic Insights into Sulfur Relay by Multiple Sulfur Mediators Involved in Thiouridine Biosynthesis at tRNA Wobble Positions

The wobble bases of bacterial tRNAs responsible for NNR codons are modified to 5-methylaminomethyl-2-thiouridine (mnm5s2U). 2-thio modification of mnm5s2U is required for accurate decoding and essential for normal cell growth. We identified five genes yhhP, yheL, yheM, yheN, and yccK (named tusA, tusB, tusC, tusD, and tusE, respectively) that are essential for 2-thiouridylation of mnm5s2U by a systematic genome-wide screen ("ribonucleome analysis"). Efficient 2-thiouridine formation in vitro was reconstituted with recombinant TusA, a TusBCD complex, TusE, and previously identified IscS and MnmA. The desulfurase activity of IscS is stimulated by TusA binding. IscS transfers the persulfide sulfur to TusA. TusE binds TusBCD complex and stimulates sulfur transfer from TusA to TusD. TusE also interacts with an MnmA-tRNA complex. This study revealed that 2-thiouridine formation proceeds through a complex sulfur-relay system composed of multiple sulfur mediators that select and facilitate specific sulfur flow to 2-thiouridine from various pathways of sulfur trafficking.

Seasonal Changes in the Structure of the Anoxygenic Phototrophic Bacterial Community in Lake Mogilnoe, a Relict Lake on Kil'din Island in the Barents Sea

An anaerobic phototrophic bacterial community in Lake Mogilnoe, a relict lake on Kil'din Island in the Barents Sea, was studied in June 1999 and September 2001. Irrespective of the season, the upper layer of the anaerobic zone of this lake had a specific species composition of sulfur phototrophic bacteria, which were dominated by the brown-colored green sulfur bacterium Chlorobium phaeovibrioides. The maximum number of phototrophic sulfur bacteria was observed in June 1999 at a depth of 9 m, which corresponded to a concentration of bacteriochlorophyll (Bchl) e equal to 4.6 mg/l. In September 2001, the maximum concentration of this pigment (3.4 mg/l) was found at a depth of 10 m. In both seasons, the concentration of Bchl a did not exceed 3 microg/l. Purple sulfur bacteria were low in number, which can be explained by their poor adaptation to the hydrochemical and optical conditions of the Lake Mogilnoe water. In June 1999, the water contained a considerable number of Pelodictyon phaeum microcolonies and Prosthecochloris phaeoasteroides cell chains, which was not the case in September 2001. A 16S rDNA-based phylogenetic analysis of pure cultures of phototrophic bacteria isolated from the lake water confirmed that the bacterial community is dominated by Chl. phaeovibrioides and showed the presence of three minor species, Thiocvstis gelatinosa, Thiocapsa sp., and Thiorhodococcus sp., the last of which is specific to Lake Mogilnoe.

The performance of an anaerobic sequencing batch biofilm reactor treating domestic sewage colonized by anoxygenic phototrophic bacteria

There are few reports on morphological characterization of microbial population colonizing anaerobic bioreactors and the aim of this work was to access such variable in an anaerobic sequencing batch biofilm reactor treating the University of Sao Paulo (Sao Carlos city, Brazil) domestic sewage. This pilot-scale reactor (1.2 m 3) has been treating 0.65 m 3 of liquid waste under cycles of 8 h. The ASBBR has the distinct characteristics of being filled with support material for biomass attachment with the aim of skipping the sedimentation phase during the operational cycles, as it is commonly observed in anaerobic sequencing batch reactors (ASBR). Physical, chemical and physico-chemical variables were accessed in the influent and in the effluent for performance evaluation. Microbial characterization was made by means of direct microscopy and samples were taken over 150 d with a 25 d period interval. The ASBBR attained approximately 60% of COD removal efficiency. Microscopic analysis of biomass showed the presence of anoxygenic phototrophic bacteria probably influencing the ASBBR performance in the domestic sewage treatment. It is very likely that the exclusion of phototrophic sulfur bacteria by efficiently restraining the light would enhance the bioreactor efficiency.

Long-Term Population Dynamics of Phototrophic Sulfur Bacteria in the Chemocline of Lake Cadagno, Switzerland

Population analyses in water samples obtained from the chemocline of crenogenic, meromictic Lake Cadagno, Switzerland, in October for the years 1994 to 2003 were studied using in situ hybridization with specific probes. During this 10-year period, large shifts in abundance between purple and green sulfur bacteria and among different populations were obtained. Purple sulfur bacteria were the numerically most prominent phototrophic sulfur bacteria in samples obtained from 1994 to 2001, when they represented between 70 and 95% of the phototrophic sulfur bacteria. All populations of purple sulfur bacteria showed large fluctuations in time with populations belonging to the genus Lamprocystis being numerically much more important than those of the genera Chromatium and Thiocystis. Green sulfur bacteria were initially represented by Chlorobium phaeobacteroides but were replaced by Chlorobium clathratiforme by the end of the study. C. clathratiforme was the only green sulfur bacterium detected during the last 2 years of the analysis, when a shift in dominance from purple sulfur bacteria to green sulfur bacteria was observed in the chemocline. At this time, numbers of purple sulfur bacteria had decreased and those of green sulfur bacteria increased by about 1 order of magnitude and C. clathratiforme represented about 95% of the phototrophic sulfur bacteria. This major change in community structure in the chemocline was accompanied by changes in profiles of turbidity and photosynthetically available radiation, as well as for sulfide concentrations and light intensity. Overall, these findings suggest that a disruption of the chemocline in 2000 may have altered environmental niches and populations in subsequent years.

Novel Genes of the dsr Gene Cluster and Evidence for Close Interaction of Dsr Proteins during Sulfur Oxidation in the Phototrophic Sulfur Bacterium Allochromatium vinosum

Seven new genes designated dsrLJOPNSR were identified immediately downstream of dsrABEFHCMK, completing the dsr gene cluster of the phototrophic sulfur bacterium Allochromatium vinosum D (DSM 180(T)). Interposon mutagenesis proved an essential role of the encoded proteins for the oxidation of intracellular sulfur, an obligate intermediate during the oxidation of sulfide and thiosulfate. While dsrR and dsrS encode cytoplasmic proteins of unknown function, the other genes encode a predicted NADPH:acceptor oxidoreductase (DsrL), a triheme c-type cytochrome (DsrJ), a periplasmic iron-sulfur protein (DsrO), and an integral membrane protein (DsrP). DsrN resembles cobyrinic acid a,c-diamide synthases and is probably involved in the biosynthesis of siro(heme)amide, the prosthetic group of the dsrAB-encoded sulfite reductase. The presence of most predicted Dsr proteins in A. vinosum was verified by Western blot analysis. With the exception of the constitutively present DsrC, the formation of Dsr gene products was greatly enhanced by sulfide. DsrEFH were purified from the soluble fraction and constitute a soluble alpha(2)beta(2)gamma(2)-structured 75-kDa holoprotein. DsrKJO were purified from membranes pointing at the presence of a transmembrane electron-transporting complex consisting of DsrKMJOP. In accordance with the suggestion that related complexes from dissimilatory sulfate reducers transfer electrons to sulfite reductase, the A. vinosum Dsr complex is copurified with sulfite reductase, DsrEFH, and DsrC. We therefore now have an ideal and unique possibility to study the interaction of sulfite reductase with other proteins and to clarify the long-standing problem of electron transport from and to sulfite reductase, not only in phototrophic bacteria but also in sulfate-reducing prokaryotes.