Novel Aspects of Iron Sulfur Cluster Biosynthesis in Sulfate Reducing Bacteria (768.17)

Iron sulfur (FeS) cluster containing proteins are involved in processes targeted by environmentally relevant stressors. These stress conditions, for sulfate reducing bacteria (SRBs) such as Desulfovibro vulgaris Hildenborough (DvH) and Desulfovibrio alaskensis G20, would include exposure to oxygen (and oxygen radicals), the presence of N‐oxyanions such as nitrate and nitrite, and exposure to potentially toxic metals such as selenium, cobalt and chromium. Significantly, FeS cluster damage in key enzymes such as pyruvate‐ferredoxin oxidoreductase (PFOR) has been proposed as the source of inviability of SRBs and other anaerobes when encountering oxygen. Some FeS cluster biosynthesis key factors have been identified in these SRBs by sequence homology. We are characterizing the effect of these mutations on key FeS dependent marker enzymes, including PFOR, formate dehydrogenase and dissimilatory sulfite reductase, in order to determine relative contributions of these factors to FeS cluster biosynthesis. Concurrently, we have also performed fitness profiling of a comprehensive G20 mutant pool under stress conditions known to damage FeS enzymes. We have observed mild fitness defects for the G20 Dde_1444/1445 (sufBC) mutant strains, consistent with reduced marker FeS enzyme activities of the DvH sufB mutant. Interestingly, fitness data has indicated that the sole cysteine desulfurase mutant in G20 (nifS; Dde_3078) displays pleotropic defects, but remains viable, contradicting current dogma regarding FeS cluster biosynthesis.Grant Funding Source: Supported by the U. S. Department of Energy under Contract No. DE‐AC02‐05CH11231