Lactobacillus kefiranofaciens, the sole dominant and stable bacterial species, exhibits distinct morphotypes upon colonization in Tibetan kefir grains

Tibetan kefir grains (TKGs), natural starters for milk fermentation, are believed to comprise diverse microflora of lactic acid and acetic acid bacteria. In order to better understand the bacterial community in TKGs, TKGs that had been cultured continuously either naturally or aseptically for 10 months were subject to analysis using both culture-dependent and various culture-independent methods. Results of DGGE, metagenomics, FISH, qPCR and isolation all demonstrated that Lactobacillus kefiranofaciens is the only dominant and stable bacterial species in TKGs regardless of culture conditions and time. FISH and SEM showed that L. kefiranofaciens exhibited two distinct morphotypes of short rod (3.0 μm in length) and long rod (10.0 μm in length) upon colonization of either the outer surface or inner component of TKGs, providing evidence for its trophic adaptation to the hollow globular grain structure of TKGs. These findings pave ways for further study of the specific symbiotic interaction between L. kefiranofaciens and the dominant Saccharomyces cerevisiae yeast in TKGs in vivo.