SULFITE REDUCTION IN SHEWANELLA ONEIDENSIS MR-1 REQUIRES TAT SECRETION SYSTEM
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Background: Shewanella oneidensis MR-1 is a gram negative facultative anaerobe that uses soluble and insoluble terminal electron acceptors for respiration. These include Fe(III) oxides, DMSO, fumarate, elemental sulfur, and sulfite. Previous work on sulfite reduction have identified SirA as a terminal sulfite reductase in Shewanella oneidensis MR-1. However not much is known about other genes that contribute to sulfite reduction process. In this study we isolated transposon mutants in twin arginine transocation system and identified their role in sulfite reduction process.
Objective: To identify the role of twin arginine secretion system in sulfite reduction of Shewanella oneidensis MR-1.
Methods: Transposon mutagenesis of Shewanella oneidensis MR-1 with pMini Himar RB1 was used to isolate mutants deficient in sulfite reduction. These consisted of mutants deficient in twin arginine transport (tatC, tatA) .Further the wild type and the mutant’s strains were analyzed by qualitative and quantitative sulfite reduction assay.
Result: The wildtype strain of Shewanella oneidensis MR-1 reduced 10 mM of sulfite within 3 days with resultant production of H2S. Sulfite reduction was also coupled to growth as indicated by increase in total protein content from 38 to 703 ugs by the end of 72 hrs of incubation. On the other hand the tatA and tatC mutant strains were completely deficient in sulfite utilization and they did not produce any detectable amount of H2S.
Conclusion: This study suggest that the terminal sulfite reductase (or components of the sulfide reduction system) may be transported to the periplasmic space through the twin arginine transport system. Based on sequence analysis it may be involved in transport of SirC protein. Additional studies are required to confirm the secretion of SirC protein by twin arginine translocation system and its role in sulfite reduction in Shewanella oneidensis MR-1.
Key Words: Sulfite reduction, Shewanella oneidensis MR-1, TAT secretion system