Mathematical simulation of the interactions among cyanobacteria, purple sulfur bacteria and chemotrophic sulfur bacteria in microbial mat communities

Abstract: A deterministic one-dimensional reaction diffusion model was constructed to simulate benthic stratification patterns and population dynamics of cyanobacteria, purple and colorless sulfur bacteria as found in marine microbial mats. The model involves the major biogeochemical processes of the sulfur cycle and includes growth metabolism and their kinetic parameters as described from laboratory experimentation. Hence, the metabolic production and consumption processes are coupled to population growth. The model is used to calculate benthic oxygen, sulfide and light profiles and to infer spatial relationships and interactions among the different populations. Furthermore, the model is used to explore the effect of different abiotic and biotic environmental parameters on the community structure. A strikingly clear pattern emerged of the interaction between purple and colorless sulfur bacteria: either colorless sulfur bacteria dominate or a coexistence is found of colorless and purple sulfur bacteria. The model predicts that purple sulfur bacteria only proliferate when the studied environmental parameters surpass well-defined threshold levels. However, once the appropriate conditions do occur, the purple sulfur bacteria are extremely successful as their biomass outweighs that of colorless sulfur bacteria by a factor of up to 17. The typical stratification pattern predicted closely resembles the often described bilayer communities which comprise a layer of purple sulfur bacteria below a cyanobacterial top-layer; colorless sulfur bacteria are predicted to sandwich in between both layers. The profiles of oxygen and sulfide shift on a diel basis similarly as observed in real systems.     

Molecular genetic evidence for extracytoplasmic localization of sulfur globules in Chromatium vinosum

Purple sulfur bacteria store sulfur as intracellular globules enclosed by a protein envelope. We cloned the genes sgpA, sgpB, and sgpC, which encode the three different proteins that constitute the sulfur globule envelope of Chromatium vinosum D (DSMZ 180^T). Southern hybridization analyses and nucleotide sequencing showed that these three genes are not clustered in the same operon. All three genes are preceded by sequences resembling σ⁷⁰-dependent promoters, and hairpin structures typical for rho-independent terminators are found immediately downstream of the translational stop codons of sgpA, sgpB, and sgpC. Insertional inactivation of sgpA in Chr. vinosum showed that the presence of only one of the homologous proteins SgpA and SgpB suffices for formation of intact sulfur globules. All three sgp genes encode translation products which – when compared to the isolated proteins – carry amino-terminal extensions. These extensions meet all requirements for typical signal peptides indicating an extracytoplasmic localization of the sulfur globule proteins. A fusion of the phoA gene to the sequence encoding the proposed signal peptide of sgpA led to high specific alkaline phosphatase activities in Escherichia coli, further supporting the envisaged targeting process. Together with electron microscopic evidence these results provide strong indication for an extracytoplasmic localization of the sulfur globules in Chr. vinosum and probably in other Chromatiaceae. Extracytoplasmic formation of stored sulfur could contribute to the transmembranous Δp that drives ATP synthesis and reverse electron flow in Chr. vinosum. Received: 1 October 1997 / Accepted: 17 December 1997     

Measuring the pH dependence of hydrogenase activities

The pH dependences of activities of homogenous hydrogenases of Thiocapsa roseopersicina and Desulfomicrobium baculatum in the reaction of hydrogen uptake in solution in the presence of benzyl viologen and the pH dependences of catalytic currents of hydrogen oxidation by electrodes on which these hydrogenases were immobilized were compared. Maximal activities of the hydrogenases from T. roseopersicina and D. baculatum in the reaction hydrogen uptake in solution were observed at pH 9.5 and 8.5, respectively. However, the steady-state current caused by catalytic uptake of hydrogen was maximal for the T. roseopersicina hydrogenase-containing electrode at pH 5.5-6.5 under overvoltage of 30-60 mV, whereas for electrodes with D. baculatum hydrogenase it was maximal at pH 6.0-6.5. Analysis of these data suggests that pH-dependent changes in the hydrogenase activities in solution during hydrogen uptake are due not only to the effect of proton concentration on the enzyme conformation or protonation of certain groups of the enzyme active center, but they are rather indicative of changes in free energy of the reaction accompanying changes in pH.     

Coexistence of aerobic chemotrophic and anaerobic phototrophic sulfur bacteria under oxygen limitation

Abstract: The aerobic chemotrophic sulfur bacterium Thiobacillus thioparus T5 and the anaerobic phototrophic sulfur bacterium Thiocapsa roseopersicina M1 were co-cultured in continuously illuminated chemostats at a dilution rate of 0.05 h⁻¹. Sulfide was the only externally supplied electron donor, and oxygen and carbon dioxide served as electron acceptor and carbon source, respectively. Steady states were obtained with oxygen supplies ranging from non-limiting amounts (1.6 mol O₂ per mol sulfide, resulting in sulfide limitation) to severe limitation (0.65 mol O₂ per mol sulfide). Under sulfide limitation Thiocapsa was competitively excluded by Thiobacillus and washed out. Oxygen/sulfide ratios between 0.65 and 1.6 resulted in stable coexistence. It could be deduced that virtually all sulfide was oxidized by Thiobacillus . The present experiments showed that Thiocapsa is able to grow phototrophically on the partially oxidized products of Thiobacillus . In pure Thiobacillus cultures in steady state extracellular zerovalent sulfur accumulated, in contrast to mixed cultures. This suggests that a soluble form of sulfur at the oxidation state of elemental sulfur is formed by Thiobacillus as intermediate. As a result, under oxygen limitation colorless sulfur bacteria and purple sulfur bacteria do not competitively exclude each other but can coexist. It was shown that its ability to use partially oxidized sulfur compounds, formed under oxygen limiting conditions by Thiobacillus , helps explain the bloom formation of Thiocapsa in marine microbial mats.     

Ammonia inhibition of nitrogenase activity in purple and green bacteria

Ammonia reversibly inhibits the nitrogenase activity not only in purple nonsulfur bacteria but in purple (Thiocapsa roseopersicina) and green (Chlorobium limicola forma thiosulfatophilum) sulfur bacteria as well.The complete inhibition of nitrogenase activity (acetylene reduction) is observed about 30 s after addition of NH ₄ ⁺ (2.5×10^-6 M) to cell suspensions. The pattern of ammonia inhibition of acetylene reduction in T. roseopersicina does not differ from the action of tetrabutylammonium and tetraphenylphosphonium (3 · 10^-6-5·10^-5 M) on nitrogenase activity of this bacterium.Simultaneously with the switch-off effect of NH ₄ ⁺ a considerable increase of ATP in cells of Rhodobacter sphaeroides and C. limicola f. thiosulphatophilum was observed.     

Bacteriological studies on the sulfur cycle in the anaerobic part of the hypolimnion and in the surface sediments of rotsee in Switzerland scientific report of the advanced course of microbial ecology, sponsored by FEMS and the Swiss society for Microbiology, held at Kastanienbaum, Switzerland, 12 September–9 October 1982

Abstract The microbial ecology of the sulfur cycle in the anaerobic part of Rotsee (Switzerland) was studied. Almost all the sulfate reduction took place at the sediment surface at a rate of 2 mmol SO²⁻₄ reduced m⁻² day⁻¹. Approx. 10⁴ sulfate reducers per ml were present in the surface sediments. The sulfide produced was phototrophically consumed mainly by Thiopedia rosea, Lamprocystis roseopersicina and ' Pelochromatium roseum ' consortia. Thiopedia rosea migrated diurnally about one meter. Bacterial photosynthesis was limited by light and sulfide rather than by temperature.     

Osmoadaptation of Thiocapsa roseopersicina OP-1 in batch and continuous culture: Accumulation of K+ and sucrose in response to osmotic stress

Abstract Increasing growth medium NaCl concentration inhibited the growth of Thiocapsa roseopersicina OP-1 due to both an increase in the lag phase of the growth cycle and a reduction in specific growth rate. Addition of 0.05% w/v acetate to the growth medium stimulated growth at all NaCl concentrations, but this stimulation was greatest at supra-optimal NaCl concentrations. Optimal growth under all conditions tested in both batch and continuous culture was recorded at a salt concentration of 0.3 M NaCl. The intracellular concentrations of both K⁺ and sucrose increased linearly with increasing growth medium NaCl concentration indicating as osmoregulatory role for these solutes. Time courses of osmoadaptation in batch culture demonstrated a biphasic response to osmotic stress. The initial phase consisted of a rapid accumulation (within 30 min) of K⁺ from the growth medium. This was followed by a slower synthesis of sucrose which partially replaced intracellular K⁺ during the second phase of osmoadaptation.     

Utilization of nitrogen compounds and ammonia assimilation by chromatiaceae

Chromatium vinosum strain D, Thiocapsa roseopersicina strain 6311 and Ectothiorhodospira mobilis strain 8112 were grown anaerobically in the light with various single nitrogen sources. When substituted for NH₄Cl only glutamine and casamino acids supported good growth of all strains tested. Peptone and urea were utilized by C. vinosum and T. roseopersicina, glutamate, asparagine and nitrate only by C. vinosum. The strains were able to grow with molecular nitrogen; complete inhibition of this growth was observed in the presence of alanine with E. mobilis, and of alanine or asparagine with T. roseopersicina.Glutamate dehydrogenase, requiring either NADH or NADPH, NADH-linked glutamate synthase, and glutamine synthetase were demonstrate in the above organisms grown on NH₄Cl.     

The effect of sulfur compounds on H<Subscript>2</Subscript> evolution/consumption reactions,mediated by various hydrogenases,in the purple sulfur bacterium, <Emphasis Type="Italic">Thiocapsa roseopersicina</Emphasis>

The influence of reduced sulfur compounds (including stored S⁰) on H₂ evolution/consumption reactions in the purple sulfur bacterium, Thiocapsa roseopersicina BBS, was studied using mutants containing only one of the three known [NiFe] hydrogenase enzymes: Hox, Hup or Hyn. The observed effects depended on the kind of hydrogenase involved. The mutant harbouring Hox hydrogenase was able to use S₂O₃²⁻, SO₃²⁻, S²⁻ and S⁰ as electron donors for light-dependent H₂ production. Dark H₂ evolution from organic substrates via Hox hydrogenase was inhibited by S⁰. Under light conditions, endogenous H₂ uptake by Hox or Hup hydrogenases was suppressed by S compounds. СО₂-dependent H₂ uptake by Hox hydrogenase in the light required the additional presence of S compounds, unlike the Hup-mediated process. Dark H₂ consumption via Hyn hydrogenase was connected to utilization of S⁰ as an electron acceptor and resulted in the accumulation of H₂S. In wild type BBS, with high levels of stored S⁰, dark H₂ production from organic substrates was significantly lower, but H₂S accumulation significantly higher, than in the mutant GB1121(Hox⁺). There is a possibility that H₂ produced via Hox hydrogenase is consumed by Hyn hydrogenase to reduce S⁰.