BIFIDOBACTERIUM LACTIS SP-NOV, A MODERATELY OXYGEN TOLERANT SPECIES ISOLATED FROM FERMENTED MILK

A selection procedure was developed to isolate Bifidobacterium strains from food and faeces which are able to grow under oxidative stress co nditions. Strain UR1, an isolate from a French yoghurt, was able to gr ow at elevated oxygen concentrations above 5% oxygen in liquid media c ontaining 0.3 mM paraquat (methylviologen). In fermenter cultures, str ain UR1 produced considerable amounts of formate (up to 23 mM) dependi ng on the oxygen-stress conditions. We sequenced the 163 rRNA gene clo ned from UR1 genomic DNA, compared it with that from 21 Bifidobacteriu m species and constructed a phylogenetic tree by alignment analysis. T he most related species of strain UR1 was calculated to be Bifidobacte rium animalis DSM 20104. DNA-DNA hybridizations between the genomes of strain UR1, B. animalis DSM 20104 and B. longum DSM 20219 showed only weak homology (27% and <10%, respectively). Both findings strongly su pported a distinct species-status for strain UR1. In addition, propert ies like enzyme profiles (API ZYM), utilization of carbohydrates (API CH 50), the G+C content of 61.9 mol% and the high tolerance towards ox ygen stress differ from those of B. animalis. Therefore, we concluded that strain UR1 has to be regarded as a new species which vile named B ifi-dobacterium lactis. This name honours the fact that the species ha s been isolated on several occasions from fermented milk.