No abstract

A wide variety of microbes use sulfonate-sulfur as the sole sulfur source for biosynthesis even when the carbon of that sulfonate cannot be used as an energy source for growth. Our studies of bacteria, including members of the genera Comamonas and Escherichia, as well as ascomycetous and basidiomycetous yeasts indicate that the sulfur of many naturally-occurring sulfonates can be reduced and assimilated into cellular sulfur compounds during aerobic, respiratory growth. Other unrelated bacteria (e.g. members of the genera Clostridium, Klebsiella) are able to use sulfonate-sulfur for biosynthesis under anaerobic conditions. Sulfonate can also serve as the terminal electron acceptor for Desulfovibrio's anaerobic respiration. The breadth of microbial participation in sulfonate-sulfur transformations in the natural sulfur cycle is thus established.Sulfonates, organosulfur compounds containing the R-CH n -S0 3 H moiety, occur in the biosphere as a result of synthesis by diverse organisms and introduction by human activity. Naturally-produced sulfonates (see Table I for some examples) include taurine in the hearts and/or eyes of vertebrates (7, 2), coenzyme M in the methanogenic Archaea (3), aeruginosin, a pigment in some pseudomonads (4), the sulfonolipids of gliding bacteria (5) and diatoms (6), taurocholic acid in the digestive system of many mammals (7), sulfolactate in Bacillus subtilis spores (8), and isethionate in the axoplasm of squid (9). Some natural sulfonates are secondary products of the breakdown of other sulfur compounds. Methanesulfonate, for instance, is a product of the chemical oxidation in the atmosphere of dimethylsulfide (10, 11) which is produced by phytoplankton (12-14) and marsh grass (75). Thus, these biosynthesized sulfonates range from very simple short chains to aromatic structures. Examples of commercially-produced sulfonates include laboratory buffers such as HEPES, MOPS, and MES, the aminobenzenesulfonates which are used in the manufacture of dyes (16) and optical brighteners, the detergent-additive toluenesulfonate (77), and linear alkylsulfonate surfactants (18).It is to be expected that the naturally-occurring sulfonates, at least, would be 0097-6156/95/0612-0365$12.00/0

Chemoautotrophic endosymbionts residing in Solemya velum gills provide this shallow water clam with most of its nutritional requirements. The cbb gene cluster of the S. velum symbiont, including cbbL and cbbS, which encode the large and small subunits of the carbon-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO), was cloned and expressed in Escherichia coli. The recombinant RubisCO had a high specific activity, approximately 3 micromol min(-1) mg protein (-1), and a KCO2 of 40.3 microM. Based on sequence identity and phylogenetic analyses, these genes encode a form IA RubisCO, both subunits of which are closely related to those of the symbiont of the deep-sea hydrothermal vent gastropod Alviniconcha hessleri and the photosynthetic bacterium Allochromatium vinosum. In the cbb gene cluster of the S. velum symbiont, the cbbLS genes were followed by cbbQ and cbbO, which are found in some but not all cbb gene clusters and whose products are implicated in enhancing RubisCO activity post-translationally. cbbQ shares sequence similarity with nirQ and norQ, found in denitrification clusters of Pseudomonas stutzeri and Paracoccus denitrificans. The 3' region of cbbO from the S. velum symbiont, like that of the three other known cbbO genes, shares similarity to the 3' region of norD in the denitrification cluster. This is the first study to explore the cbb gene structure for a chemoautotrophic endosymbiont, which is critical both as an initial step in evaluating cbb operon structure in chemoautotrophic endosymbionts and in understanding the patterns and forces governing RubisCO evolution and physiology.

Purple bactenal aggregates found in tidal pools of Great Sippewissett Salt Marsh (Falmouth, Cape Cod, MA) were mvestlgated m order to eluCidate the ecological significance of cell aggregation. Purple sulfur bactena were the dommant microorganisms m the aggregates which also con tamed diatoms and a high number of small rod-shaped bactena. Urea m concentrations of ~ 1 M caused dlsmtegratlOn of the aggregates while proteolytic enzymes, surfactants or chaotropic agents did not exhibit this effect. This suggests that polysaccharides in the embedding slime matrix stabihze the aggregate structure In addition cell surface hydrophoblclty is involved in aggregate formation. The concentration of dissolved oxygen decreased rapidly below the surface of aggregates while sulfide was not detected. The apparent respiration rate m the aggregates was high when the purple sulfur bactena contamed intracellular sulfur globules. In the presence of DCMU, respiratIOn remained hght-mhibited. Light inhibition disappeared in the presence of KCN. These results demonstrated that respiration m the aggregates IS due mamly to purple sulfur bactena The concentration of bactenochlorophyll (Bch\) a in the aggregates (0.205 mg Bchla cm -3) was much higher than m the pool sedlments but comparable to concentrations in microbial mats of adjacent sand fiats. Purple aggregates may therefore onginate m the microbial mats rather than in the pools themselves Rapid sedimentation and high resplfatlOn rates of Chromatiaceae in the aggregates would prevent the mhibitlon of Bchl syntheSIS If aggregates were hfted off the sediment and up mto the OXIC pool water by tidal currents.

Purple bactenal aggregates found in tidal pools of Great Sippewissett Salt Marsh (Falmouth, Cape Cod, MA) were mvestlgated m order to eluCidate the ecological significance of cell aggregation. Purple sulfur bactena were the dommant microorganisms m the aggregates which also con tamed diatoms and a high number of small rod-shaped bactena. Urea m concentrations of ~ 1 M caused dlsmtegratlOn of the aggregates while proteolytic enzymes, surfactants or chaotropic agents did not exhibit this effect. This suggests that polysaccharides in the embedding slime matrix stabihze the aggregate structure In addition cell surface hydrophoblclty is involved in aggregate formation. The concentration of dissolved oxygen decreased rapidly below the surface of aggregates while sulfide was not detected. The apparent respiration rate m the aggregates was high when the purple sulfur bactena contamed intracellular sulfur globules. In the presence of DCMU, respiratIOn remained hght-mhibited. Light inhibition disappeared in the presence of KCN. These results demonstrated that respiration m the aggregates IS due mamly to purple sulfur bactena The concentration of bactenochlorophyll (Bch\) a in the aggregates (0.205 mg Bchla cm -3) was much higher than m the pool sedlments but comparable to concentrations in microbial mats of adjacent sand fiats. Purple aggregates may therefore onginate m the microbial mats rather than in the pools themselves Rapid sedimentation and high resplfatlOn rates of Chromatiaceae in the aggregates would prevent the mhibitlon of Bchl syntheSIS If aggregates were hfted off the sediment and up mto the OXIC pool water by tidal currents.