The Antimicrobial Effect And Mechanism Of H₂S On The Storage Pathogens

Hydrogen sulfide （H₂S）, traditionally thought as a toxic gas, has proved to be a new gaseous signaling molecule and modulate many physiological processes in plants and animals. Previous work found that H₂S could extend the postharvest life of many fruits, whereas there is limited data on the relationships between H₂S and postharvest microbes. In this research, the antimicrobial effect of H₂S on the postharvest pathogens （Aspergillus niger, etc） and food-borne bacteria （Escherichia coli, etc） and its possible mechanism were investigated. Results show that H₂S, released by sodium hydrosulfide （NaHS） effectively reduced the postharvest decay of fruits induced by A. niger and Penicillium italicum. Furthermore, H₂S inhibited spore germination, germ tube elongation, mycelial growth, and produced abnormal mycelial contractions when the fungi were grown on defined media in Petri plates. Further studies showed that H₂S could cause an increase in intracellular reactive oxygen species （ROS） and DNA oxidative damage in A. niger. In accordance with this observation we showed that enzyme activities and the expression of superoxide dismutase （SOD） and catalase （CAT） genes in A. niger treated with H₂S were lower than those in control.Moreover, H₂S significantly inhibited the growth of E. coli, Salmonella sp., Staphyloccocus aureus, Listeria sp. when the bacteria were grown on defined media in Petri plates. H₂S also inhibited the enzyme activities of SOD, CAT and glutathione reductase （GR）, decreased GSH content, stimulated ROS burst, induced the SoxR and OxyR response as well as caused lipid peroxidation and DNA oxidative damage in E. coli. Besides, pretreatment with ascorbic acid （AsA） effectively prevented H₂S-induced toxicity to E. coli. Moreover, H₂S also significantly inhibited the growth of Saccharomyces cerevisiae, Candida albicans, Bacillus subtilis, Bacillus thuringiensis, Enterobacter aerogenes. We also found that short time exposure of higher concentration H₂S showed a microbicidal role.This investigation also created the catA and cpeB gene knock-out vector, and separately transformed them into protoplast by applying the PEG transformation method, finally constructing the A. niger catA deletion mutant and cpeB deletion mutant. Further research showed that AcatA presented non-significant sensibility to H₂O2 and H₂S stress used in this work compared with wild type, whereas AcpeB exhibited more sensitivity to both H₂O2 and H₂S stress, indirectly suggesting that H₂S inhibited microbial growth through causing oxidative damage. Taken together, this study suggests the potential value of H₂S in reducing postharvest loss and food spoilage caused by microbe propagation.