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It was previously discovered that, in the Gram-negative bacterium Escherichia coli growing on a minimal medium with sulfate, stress-induced growth arrest is accompanied by the release of hydrogen sulfide. The source of the sulfide is the desulfurization of intracellular cysteine as one of the ways of maintaining it at a safe level. The danger of excess cysteine is associated with its participation in the Fenton reaction, leading to the formation of highly toxic hydroxyl radicals. Using electrochemical sensors, we identified stress-induced sulfide production in the Gram-positive bacteria Bacillus subtilis and Bacillus megaterium, growing on a minimal medium with sulfate, and changes in physiological parameters such as Eh, pH, and oxygen and potassium consumption. Sulfide production was observed during growth arrest due to the depletion of glucose, ammonium or antibiotic action. The use of sensors allowed to continuously record, in growing cultures, even small changes in parameters. There were significant differences in the amount and kinetics of sulfide production between Bacillus and E. coli. These differences are thought to be due to the lack of glutathione in Bacillus. It is suggested that stress-induced sulfide production by Bacillus under the described conditions may be one of the previously unknown sources of hydrogen sulfide in nature. [ABSTRACT FROM AUTHOR]

The ability of hydrogen sulfide (H2S) to protect bacteria from bactericidal antibiotics has previously been described. The main source of H2S is the desulfurization of cysteine, which is either synthesized by cells from sulfate or transported from the medium, depending on its composition. Applying electrochemical sensors and a complex of biochemical and microbiological methods, changes in growth, respiration, membrane potential, SOS response, H2S production and bacterial survival under the action of bactericidal ciprofloxacin and bacteriostatic chloramphenicol in commonly used media were studied. Chloramphenicol caused a sharp inhibition of metabolism in all studied media. The physiological response of bacteria to ciprofloxacin strongly depended on its dose. In rich LB medium, cells retained metabolic activity at higher concentrations of ciprofloxacin than in minimal M9 medium. This decreased number of surviving cells (CFU) by 2–3 orders of magnitude in LB compared to M9 medium, and shifted optimal bactericidal concentration (OBC) from 0.3 µg/mL in M9 to 3 µg/mL in LB. Both drugs induced transient production of H2S in M9 medium. In media containing cystine, H2S was produced independently of antibiotics. Thus, medium composition significantly modifies physiological response of E. coli to bactericidal antibiotic, which should be taken into account when interpreting data and developing drugs. [ABSTRACT FROM AUTHOR]

Treatment of aerobic Escherichia coli K 12 with nonlethal doses of near-ultraviolet (NUV) and HO resulted in the same physiological response. In response to stress caused by these agents, an inhibition of growth, a decrease in intracellular K pool, and an increase in intracellular levels of protein and nonprotein thiols were observed. A possible role for glutathione in the process of adaptation of E. coli culture to growth under the conditions of oxidative stress is discussed. [ABSTRACT FROM AUTHOR]

Tannic (TA) and gallic (GA) acids are known to have both anti- and prooxidant properties however recently they have been described as potential anti-biofilm agents although their mechanisms of action on bacterial cells remain obscure. The aim of our research was to elucidate the role of prooxidant actions of these plant phenolic compounds in bactericidal effects and biofilm formation. In our experiments, both compounds demonstrated strong oxidative properties that altered activity of stress regulons and contributed to decrease of CFU and ability of cells to maintain membrane potential. Stimulation of biofilm formation was observed in all the strains with the exception of the strains deficient in flagella synthesis. Both compounds demonstrated bactericidal effect which was weakened in biofilms. TA efficiently killed bacteria in the bioflms of pgaA mutant which pointed out an important role of poly-beta-1,6-N-acetyl-D-glucosamine (PGA) polysaccharide in matrix formation. Similar effects of TA in recA mutant indicate involvement of SOS-response into reaction towards exposure with TA. Gallic acid-induced killing was more pronounced in the biofilms of csgA mutant revealing role of curli in protection against GA toxicity., Competing Interests: Conflict of interest: The authors declare that they have no conflict of interest., (© 2019 the Author(s), licensee AIMS Press.)