Diversity of grass-associated Microbacteriaceae isolated from the phyllosphere and litter layer after mulching the sward; polyphasic characterization of Subtercola pratensis sp. nov., Curtobacterium herbarum sp. nov. and Plantibacter flavus gen. nov., sp. nov.

A representative selection of coryneform bacteria, isolated from the phyllosphere of grasses and the litter layer after mulching the sward, was characterized by a polyphasic approach to clarify their taxonomic position in the family Microbacteriaceae, with particular reference to potentially plant-pathogenic bacteria. On the basis of 16S rDNA analysis, the isolates can be classified into six genotypes representing the genera Curtobacterium, Clavibacter, Subtercola and a subgroup, which was not affiliated to a known genus. One genotype, belonging to the genus Curtobacterium, had an identical 16S rDNA sequence to reference strains of the Curtobacterium flaccumfaciens pathovars. Another genotype, closely related to the potentially pathogenic Curtobacterium flaccumfaciens, could be distinguished from known species of the genus on the basis of phylogenetic and phenotypic characterization and is consequently proposed as a novel species, Curtobacterium herbarum sp. nov. (type strain P 420/07T DSM 14013T = LMG 19917T). Two genotypes assigned to Clavibacter showed a close relationship to Clavibacter michiganensis subsp. tessellarius, a pathogenic bacterium causing foliar lesions on wheat. A further genotype, which clustered clearly in the genus Subtercola by comparison of 16S rDNA sequences, showed a hitherto undescribed B-type of peptidoglycan containing the diagnostic diamino acids ornithine and 2,4-diaminobutyric acid, in the cell wall; this genotype is proposed as Subtercola pratensis sp. nov. (type strain P 229/10T = DSM 14246T = LMG 21000T). For one genotype, which formed a phylogenetically separate branch in the family of Microbacteriaceae showing chemotaxonomic similarities to the genus Rathayibacter, a novel genus, Plantibacter gen. nov., is proposed; the type species is Plantibacter flavus sp. nov. (type strain P 297/02T = DSM 14012T = LMG 19919T).