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Transcriptomic analysis demonstrates that low-molecular weight thiols have different functions in heterotrophic and autotrophic bacteria
Bacteria must be able to withstand a myriad of stresses from both their environment, and in the case of pathogens, from their host. Low molecular weight thiols serve as redox buffers to maintain a reducing environment in the cell and participate in various protective mechanisms, including detoxification of reactive oxygen and nitrogen species, resistance against electrophiles and antibiotics, and protection against environmental stressors. In this study, I analyze the transcriptome of two heterotrophic clinically relevant bacteria, Pseudomonas aeruginosa PAO1 and Staphylococcus aureus SAUSA300 and transposon mutants disrupted in thiol biosynthesis. The transposon mutants are disrupted in P. aeruginosa glutathione biosynthesis gene, gshA, and S. aureus bacillithiol biosynthesis gene, bshC. I also analyze the transcriptome of the autotrophic cyanobacterium, Synechocystis PCC 6803 as well as a knock-out mutant disrupted in egtB, which is involved in ergothioneine biosynthesis. P. aeruginosa gshA mutant is downregulated in type II and type VI secretion systems and upregulated in type III secretion systems while the S. aureus bshA mutant is downregulated in type VII secretion suggesting that thiols play a role in secretion of effectors. Strikingly, both P. aeruginosa and S. aureus switch to anerobic respiration with nitrate as the electron acceptor in the thiol mutants. A number of other virulence factors are also differentially expressed in these mutants agreeing with the attenuation of the mutants in disease models. In contrast, genes related to high light resistance, acid stress tolerance, and osmotic stress tolerance are downregulated in Synechocystis PCC 6803. This suggests that ergothioneine is involved in abiotic stress tolerance in the autotrophic bacteria. Overall, we demonstrate that LMW thiols are involved in a myriad of functions have not been previously identified.