Bifidobacterium psychraerophilum sp. nov. and Aeriscardovia aeriphila gen. nov., sp. nov., isolated from a porcine caecum.

In a previous study that was based primarily on 16S rDNA sequencing, two groups of bifidobacteria that had been recovered from a pig caecum were proposed to belong to two novel species, termed 'Bifidobacterium pyschroaerophilum' and 'Bifidobacterium aerophilum'. In this study, based on DNA G+C content and partial heat-shock protein 60 (HSP60) gene sequences, the assignment of 'B. pyschroaerophilum', corrected to Bifidobacterium pyschraerophilum, to the genus Bifidobacterium was confirmed. The DNA G+C content of 'B. aerophilum' was relatively low, which was consistent with its segregation into subcluster II of the 16S rDNA phylogenetic tree. Based on partial 16S rDNA and HSP60 gene sequences, the species was transferred to a novel genus and reclassified as Aeriscardovia aeriphila gen. nov., sp. nov. Biochemical profiles and growth parameters were established for both novel species. Interestingly, each had a high tolerance to oxygen and grew on agar media under aerobic conditions, a trait that may relate to their caecal habitat. Under aerobic growth conditions, the short-rod morphology of A. aeriphila lengthened considerably. This appeared to arise from incomplete cell division. In addition, B. pyschraerophilum was unusual in that it grew at temperatures as low as 4 degrees C. On the basis of genetic, phylogenetic and phenotypic data, the identities of Bifidobacterium pyschraerophilum sp. nov. (type strain, T16(T)=LMG 21775(T)=NCIMB 13940(T)) and Aeriscardovia aeriphila gen. nov., sp. nov. (type strain, T6(T)=LMG 21773(T)=NCIMB 13939(T)) are confirmed.