Manganese and Defenses against Oxygen Toxicity in Lactobacillus plantarum

Abstract

L. plantarum is aerotolerant during log-phase growth on glucose, but is an obligate aerobe on polyols. Respiration was cyanide resistant and under certain conditions was associated with the accumulation of millimolar concentrations of H2O2. On glucose, optimal growth was observed in the absence of O2. Extracts of L. plantarum did not catalyze the reduction of paraquat by reduced NAD, but plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) was readily reduced. Such extracts produced O2- in the presence of NADH plus plumbagin. Plumbagin caused a 10-fold increase in the rate of respiration of intact cells in the presence of glucose and also imposed a loss of viability which was dependent upon glucose and 02. Although extracts of L. plantarum were devoid of true superoxide dismutase activity, this organism was comparable to superoxide dismutase-containing species in its resistance toward hyperbaric O2 and toward the oxygen-dependent lethality of plumbagin. L. plantarum required Mn-rich media and actively accumulated Mn(II). Soluble extracts contain .apprx. 9 .mu.g of Mn/mg of protein and 75-90% of this Mn was dialyzable. Such extracts exhibited a dialyzable and EDTA-inhibitable ability to scavenge O2-. This O2--scavenging activity was due to the dialyzable Mn(II) present in these extracts and could be mimicked by MnCl2. Cells grown in Mn-rich media were enriched in dialyzable Mn and were more resistant toward O2 toxicity and toward the O2-dependent plumbagin toxicity than were cells grown in Mn-deficient media. L. plantarum exhibited no nutritional requirement for Fe and little or no Fe was present in these cells, even when they were grown in Fe-rich media. L. plantarum thus appears to use millimolar levels of Mn(II) to scavenge O2-, much as most other organisms use micromolar levels of superoxide dismutases.