Sulfur Oxidation in Chlorobium tepidum (syn. Chlorobaculum tepidum): Genetic and Proteomic Analyses

Abstract

Chlorobium tepidum (syn. Chlorobaculum tepidum) has become the model system of choice for understanding the unique biological attributes of the green sulfur bacteria, the Chlorobiaceae. This chapter describes how genome sequence enabled genetic and proteomic approaches are being applied to understand pathways of anaerobic sulfur oxidation in C. tepidum. Reduced sulfur compounds are the sole source of exogenous reductant that C. tepidum utilizes to drive all anabolic pathways necessary for cellular growth, including carbon and nitrogen fixation. The stoichiometries of sulfur-compound conversions in batch cultures confirm that sulfide oxidation occurs via extracellular elemental sulfur. No intermediate is apparent for the oxidation of thiosulfate to sulfate, but thiosulfate oxidation appears to be stimulated when cells are grown autotrophically. Mutation of predicted sulfur oxidation genes leads to pleiotropic phenotypes that appear to affect the organization of photopigments in cells, suggesting that sulfur oxidation and light harvesting are tightly integrated processes in C. tepidum. In concert with genetic approaches, proteomics coupled with subcellular fractionation is being used to identify proteins that are potentially involved in the oxidation of extracellular elemental sulfur. Observations on the next generation of genetic techniques to augment those that currently exist in C. tepidum and to extend proteomic observations are presented throughout.