No abstract

The twin arginine translocation system (Tat) is a protein secretion system that is conserved in bacteria, archaea, and plants. In Gram-negative bacteria, it is required for the export of folded proteins from the cytoplasm to the periplasm. There are 30 experimentally verified Tat substrates in Salmonella, including hydrogenase subunits, enzymes required for anaerobic respiration, and enzymes involved in peptidoglycan remodeling during cell division. Multiple studies have demonstrated the susceptibility of tat mutants to antimicrobial compounds such as SDS and bile; however, in this work we use growth curves and viable plate counts to demonstrate that cell wall targeting antibiotics (penicillins, carbapenems, cephalosporins, and fosfomycin) have increased killing against a Δtat strain. Further, we demonstrate that this increased killing is primarily due to defects in translocation of critical Tat substrates: MepK, AmiA, AmiC, and SufI. Finally, we show that a ΔhyaAB ΔhybABC ΔhydBC strain has an altered ΔΨ which impacts proper secretion of critical Tat substrates in aerobic growth conditions.

Salmonella species cause an array of diseases in a variety of hosts. This research is significant in showing induction of the Tat system as a defense against periplasmic stress. Understanding the underlying mechanism of this regulation broadens our understanding of the Salmonella stress response, which is critical to the ability of the organism to cause infection.

Detoxification of the glycopeptide bleomycin is mediated by bleomycin hydrolase, a cysteine aminopeptidase identified in a variety of organisms. The opportunistic fungal pathogen Candida albicans is known to exhibit increased resistance to bleomycin when compared to other yeast. Presented here is the cloning of the C. albicans Lap3p aminopeptidase, predicted by sequence identity to be the Candida form of bleomycin hydrolase. C. albicans Lap3p is functionally capable to replace the Saccharomyces cerevisiae Lap3p in vivo. Furthermore, the Candida enzyme was found to function as a cysteine aminopeptidase in vivo. It is shown here that upon introduction into a lap3 deletion strain of S. cerevisiae, the C. albicans Lap3p aminopeptidase does not significantly alter the response of Saccharomyces to bleomycin. These results suggest that C. albicans Lap3p does not function as the sole factor involved in bleomycin detoxification, and may require an accessory protein or co-factor in order to efficiently mediate this process in Candida. This study provides the first evidence of a functional description of the C. albicans Lap3p cysteine aminopeptidase, and provides the foundation for further mechanistic studies of the role of this protein in the cellular processes of Candida.