The effects of aeration on the bioreductive abilities of some heterofermentative lactic acid bacteria

The growth in glucose media of many heterofermentative lactic acid bacteria is greatly improved by the provision of an ancillary oxidant which serves as a terminal electron sink. Lactobacillus brevis is representative of those organisms for which dioxygen is preferentially used for this purpose. Here the authors report that some other species including Lact. hilgardii, Lact. suebicus and Lact. vaccinostercus do not utilize dioxygen in this manner and consequently are able to catalyse bioreductions (e.g. of ketones) under aerobic culture conditions or in aerated cell suspension. The explanation for this lies in the NADP-dependence of their glucose 6-phosphate and 6-phosphogluconate dehydrogenases plus the total or near absence of any NADPH oxidase activity. Lactobacillus hilgardii possesses virtually no NADH oxidase activity, and although both Lact. suebicus and Lact. vaccinostercus inducibly synthesize a NADH oxidase, in the absence of an auxiliary oxidant they still grow aerobically on glucose as poorly as they do anaerobically.