Butanol :: Biology, Bacteria

Many species belonging to the genus Clostridium are categorized as stringent anaerobes because neither they nor key enzymes inside them are equal to function commonly during aerobic culti-vations, and stringent anaerobic conditions are required for their growth (1). disdain the gen-eral understanding about the sensitivity of clostridiuml species to O2, some subscriber lines possess me-tabolic mechanisms for withstanding, to some degree, the comportment of dissolved oxygen (DO), and this phenomenon has been reviewed(2,3). Clostridium acetobutylicum strain ATCC 824, a widely investigated sticker for studies on the fermentative production of butanol, sus-tained growth after a shift from anaerobic to microoxic conditions (0-0.2 % DO)at the mid-exponential phase of growth, however, it ceased to grow on flushing the broth with a gas medley of 5 % O2 / 95 % N2 (4).The O2-tolerance of C. acetobutylicum strain ATCC 824 in microoxic conditions has been attributed to the production of O2-induced polypeptides, which are presumed to conform to a protective role against toxic activated oxygen species such(prenominal) as superoxide anion and hydrogen peroxide (4).Studies on the oxygen stress-responses in the obligate anaerobes C. acetobutylicum and C.aminovalericum revealed the upregulation of gene clusters coding for O2-scavenging enzymes, including NADH rubredoxin oxidoreductase (EC 1.18.1.1), glutathione peroxidase (EC 1.11.1.9), thiol peroxidase (EC 1.11.1.1), alkylhydroperoxide reductase (EC 1.11.1.15), and superoxide dismutase (5).Based on the findings of Kawasaki et al. (4,5), Hillman et al. (6) reported that C. acetobutylicum strain ATCC 824 perRmutants, survived aerobic incubation on agar plates for up to 50 age (6). The per mutants also survived aerobic stress in aerated liquid cultures for up to 3 hours before a decrease in cell viability was notice (6). However, at this stage (after 3 hours) if no further O2 was added to the broth culture, the perR m utants were able to reestablish anaerobic conditions by rapidly consuming DO in the broth (6). These reports (4,5,6) however, did not investigate the effects of oxidative stress on the production of solvents. Despite the presence of metabolic mechanisms in some clostridia for surviving short-term oxidative stress, these appear to be insufficient for establishing semipermanent survival under aerobic conditions.Literature on the effects of oxidative stress on butanol-producing bacteria, all of which are strict anaerobes, remains limited. A fuller understanding of the effects of such stressants on metabolite production go forth provide insights into stress-specific responses in bu-tanol-producing bacteria and may reveal strategies for improving the recurrence of solvents.