Insights into the stress response and sulfur metabolism revealed by proteome analysis of a Chlorobium tepidum mutant lacking the Rubisco-like protein

A significant fraction of the proteome of Chlorobium tepidum is altered in a mutant strain of the green sulfur bacterium C. tepidum (Omega::RLP) lacking the Rubisco-like protein (RLP). Additionally, a number of stress proteins display altered abundance or migration in strain Omega:: RLP, including a thioredoxin, a putative Hsp20 family chaperonin, and GroEL. Changes in protein abundance are closely correlated to mRNA abundance in the case of two other stress proteins, a thiol-specific antioxidant protein homolog (Tsa/AhpC) and an iron only superoxide dismutase (Fe-SOD). Strain Omega::RLP is more resistant to hydrogen peroxide exposure than strain WT2321, providing evidence that the stress proteins are functional. Strain Omega::RLP is also defective in thiosulfate oxidation, but is able to oxidize sulfide as well as the wild-type strain. Based on studies with periplasm-enriched extracts of strain Omega::RLP, the loss of thiosulfate oxidation capability correlates with undetectable levels of the SoxY protein, a component of the predicted thiosulfate oxidation complex. These results provide further indications that sulfur oxidation capacity and the response to stress are linked in C. tepidum, with the RLP playing a major role.