Direct Involvement of Type II Secretion System in Extracellular Translocation of Shewanella Oneidensis Outer Membrane Cytochromes MtrC and OmcA
Outer membrane decaheme c-type cytochromes MtrC and OmcA of Shewanella oneidensis MR-1 are extracellular lipoproteins important for dissimilatory reduction of solid metal (hydr)oxides during anaerobic respiration. To investigate the roles of type II secretion system (T2S) in translocation of MtrC and OmcA across outer membrane, we measured the effects of deleting two T2S genes, gspD and gspG, on the secretion of MtrC and OmcA when cells were grown under anaerobic conditions. Deletion of gspD or gspG resulted in slightly yellowish supernatants, different from the pink supernatant of wild type (wt). Comparative proteomic analyses revealed that, although MtrC, OmcA and NrfA, a periplasmic nitrite reductase, were present the supernatants of wt and ΔgspD mutant, their peptides counts were much lower in ΔgspD than in wt. Subsequent analyses with heme-staining and Western blot not only confirmed that deletion of gspD or gspG reduced the abundances of MtrC and OmcA in the supernatants, but also revealed that the deletions consequently increased their abundances inside the cells. Complementation of ΔgspG mutant with functional GspG could reverse the effects of deleting gspG on the colors of the supernatants and the abundances of MtrC and OmcA. In contrast, Western results showed that the abundance of NrfA was reduced in the supernatant and the cells of ΔgspD mutant, suggesting that reduced NrfA in the periplasm, where MtrC and OmcA were accumulated, contributed to its reduction in the supernatant. Thus, our results demonstrate at the first time that T2S facilitates translocation of MtrC and OmcA across outer membrane.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 935063
- Report Number(s):
- PNNL-SA-55117; 12496
- Journal Information:
- Journal of Bacteriology, 190(15):5512-5516, Journal Name: Journal of Bacteriology, 190(15):5512-5516 Journal Issue: 15 Vol. 190; ISSN JOBAAY; ISSN 0021-9193
- Country of Publication:
- United States
- Language:
- English
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