Antimicrobial garlic-derived diallyl polysulfanes: Interactions with biological thiols in Bacillus subtilis.

BACKGROUND: Diallylpolysulfanes are the key constituents of garlic oils, known to exhibit broad spectrum anticancer and antimicrobial activity. Studies in vitro, and in mammalian cells, have shown they react, via thiol-polysulfane exchange, with their major low molecular weight thiol, glutathione. However, there are no detailed reports of diallylpolysulfane effects on other common thiol metabolites (cysteine and coenzyme A) or major thiol cofactors (e.g. bacillithiol) that many Gram positive bacteria produce instead of glutathione. METHODS: Diallylpolysulfanes were individually purified then screened for antimicrobial activity against Bacillus subtilis. Their impact on thiol metabolites (bacillithiol, cysteine, coenzyme A, protein thiols allyl thiols//persulfides) in B. subtilis cultures were analysed, by HPLC. RESULTS: Diallylpolysulfane bioactivity increased with increasing chain length up to diallyltetrasulfane, but then plateaued. Within two minutes of treating B. subtilis with diallyltrisulfane or diallyltetrasulfane intracellular bacillithiol levels decreased by ~90%. Cysteine and CoA were also affected but to a lesser degree. This was accompanied by the accumulation of allyl thiol and allyl persulfide. A significant level of protein-S-allylation was also detected. CONCLUSIONS: In addition to the major low molecular weight thiol, diallylpolysulfanes can also have an impact on other thiol metabolites and protein thiols. GENERAL SIGNIFICANCE: This study shows the rapid parallel impact of polysulfanes on different biological thiols inside Bacillus subtilis alongside the concomitant generation of allyl thiols and persulfides.

Think Yellow and Keep Green-Role of Sulfanes from Garlic in Agriculture.

Reactive sulfur species from garlic have long been renowned for their health benefits and antimicrobial properties. In agriculture the subject matter is now gathering momentum in the search for new bio-pesticides to addressing emerging environmental concerns and tighter restrictions on the use of many conventional chemical pesticides. Although the precise modes of action of these garlic-derived bioactives is complex, recent research has provided a number of new insights that deepen our understanding of garlic-derived products, such as garlic extracts and oils. Herein, their activity against various crop-damaging pests is reviewed. In many cases, there seems to be a broad range of activity associated with the sulfur-containing compounds derived from Allium species, which manifests itself in diverse insecticidal, antifungal, and nematicidal activities. These activities open a new understanding to develop this natural chemistry as a "green pesticide".

Biophysical features of bacillithiol, the glutathione surrogate of Bacillus subtilis and other firmicutes.

Bacillithiol (BSH) is the major low-molecular-weight (LMW) thiol in many low-G+C Gram-positive bacteria (Firmicutes). Evidence now emerging suggests that BSH functions as an important LMW thiol in redox regulation and xenobiotic detoxification, analogous to what is already known for glutathione and mycothiol in other microorganisms. The biophysical properties and cellular concentrations of such LMW thiols are important determinants of their biochemical efficiency both as biochemical nucleophiles and as redox buffers. Here, BSH has been characterised and compared with other LMW thiols in terms of its thiol pKa , redox potential and thiol-disulfide exchange reactivity. Both the thiol pKa and the standard thiol redox potential of BSH are shown to be significantly lower than those of glutathione whereas the reactivities of the two compounds in thiol-disulfide reactions are comparable. The cellular concentration of BSH in Bacillus subtilis varied over different growth phases and reached up to 5 mM, which is significantly greater than previously observed from single measurements taken during mid-exponential growth. These results demonstrate that the biophysical characteristics of BSH are distinctively different from those of GSH and that its cellular concentrations can reach levels much higher than previously reported.