Aerobic growth of some lactic acid bacteria enabled by the external addition of peroxidase (horseradish) to the culture medium

Isolation of hitherto-uncultivated microorganisms- Application of radical scavengers

The culture filtrates of the predominant bacterial strains isolated from soil samples have been shown to increase the microbial colony counts on agar plates used for the isolation of uncultured bacteria. One of the factors in the culture filtrates responsible for this increase was identified to be superoxide dismutase (SOD). The generation of reactive oxygen species (O2-, H2O2, and ・OH) was detected from conventional laboratory agar media. The use of agar media supplemented with radical scavengers (SOD, catalase, ascorbic acid, or rutin) effectively increased the colony counts and kinds of microbial strains that grew from soil samples. Taxonomical studies on these isolates revealed new taxa for phylum Actinomycetota; one family, three genera, and nine species were newly described. One of the strains, Patulibacter minatonensis KV-614T belonging to the new family Patulibacteraceae, was isolated on agar medium supplemented with SOD. P. minatonensis KV-614T represents a novel lineage within the phylum Actinomycetota. A polymerase chain reaction (PCR) study using specific primers for the detection of strains related to the genus Patulibacter, order Solirubrobacterales, showed a high distribution frequency, with detection in over 70% of the soil samples tested. These data suggest that the use of radical scavengers may facilitate the isolation of some hitherto-uncultivated microorganisms widely distributed in soil.

Aerobic and respirative growth of heterofermentative lactic acid bacteria: A screening study

Heterofermentative lactic acid bacteria (76 strains) belonging to Lactobacillus, Leuconostoc and Weissella species which are important in fermentation, spoilage or as probiotics were screened in a factorial experiment for their ability to grow, produce catalase and consume oxygen in aerobiosis or in anaerobiosis, with or without supplementation with hemin and/or menaquinone in a medium containing glucose as a carbohydrate source. Aerobiosis improved growth with a few exceptions. The effect of supplementation with heme and/or menaquinone was strain specific and clear evidence of heme-boosted respiration was found in some cases. Heme-catalase was produced by strains of L. brevis, W. minor and Leuc. mesenteroides; some strains of the latter species produced non-heme catalase. Shaken flasks experiments showed that aerobic growth resulted in increased maximum growth rate and in a limited increase in biomass. Heme supplementation during aerobic growth resulted in a further increase in growth rate and final biomass only for a few strains; this was often related to catalase, which was also responsible for increased tolerance of H₂O₂. In both experiments we found evidence of heme toxicity, especially in anaerobiosis and in absence of menaquinone. Dose response curves for aerobic growth in the presence of combinations of hemin and menaquinone were non-monotonic, with growth stimulation at low doses of heme (<2.5 mg/l) and toxicity at higher doses. Menaquinone at 0.25-8 mg/l increased growth stimulation and partially reduced toxicity.

Cholic acid is accumulated spontaneously, driven by membrane deltapH, in many lactobacilli

Many lactobacilli from various origins were found to apparently lack cholic acid extrusion activity. Cholic acid was accumulated spontaneously, driven by the transmembrane proton gradient. Accumulation is a newly identified kind of interaction between intestinal microbes and unconjugated bile acids and is different from extrusion and modification, which have been described previously.