A number of pink-pigmented facultative methylotrophs (PPFMs) belonging to Methylobacterium spp. isolated from living plant samples were found to require B vitamins for their growth in minimal medium, and most B vitamin-auxotrophic PPFMs required pantothenate (vitamin B5). Further investigation of pantothenate auxotrophy using the representative strain Methylobacterium sp. OR01 demonstrated that this strain cannot synthesize β-alanine, one of the precursors of pantothenate. β-alanine and several precursors of pantothenate restored the growth of Methylobacterium sp. OR01 in minimal medium. Furthermore, this strain could colonize leaves of Arabidopsis thaliana cultivated in medium without pantothenate or its precursors. Pantothenate, β-alanine and several precursors were detected in the suspension of A. thaliana leaves. These results suggest that pantothenate-auxotrophic PPFMs can symbiotically colonize the surface of plant leaves by acquiring β-alanine and other precursors, in addition to pantothenate. Finally, the fitness advantage of B vitamin auxotrophy of PPFMs in the phyllosphere environment is discussed.
Keywords: B vitamin auxotrophy; pantothenate; phyllosphere; β-alanine.