Physiological and genomic analyses of cobalamin (vitamin B12)-auxotrophy of Lysobacter auxotrophicus sp. nov., a methionine-auxotrophic chitinolytic bacterium isolated from chitin-treated soil.

Abstract

A novel bacterium, designated 5-21aT, isolated from chitin-treated upland soil, exhibits methionine (Met) auxotrophy and chitinolytic activity. A physiological experiment revealed the cobalamin (synonym, vitamin B12)(Cbl)-auxotrophic property of strain 5-21aT. The newly determined complete genomic sequence indicated that strain 5-21aT possesses only the putative gene for Cbl-dependent Met synthase (MetH) and lacks that for the Cbl-independent one (MetE), which implies the requirement of Cbl for Met-synthesis in strain 5-21aT. The set of genes for the upstream (corrin ring synthesis) pathway of Cbl synthesis is absent in the genome of strain 5-21aT, which explains the Cbl-auxotrophy of 5-21aT. This strain was characterized via a polyphasic approach to determine its taxonomic position. The nucleotide sequences of two copies of the 16S rRNA gene of strain 5-21aT indicated the highest similarities to Lysobacter soli DCY21T(99.8 and 99.9 %) and Lysobacter panacisoli CJ29T(98.7 and 98.8 %, respectively), whose Cbl-auxotrophic properties were revealed in this study. The principal respiratory quinone was Q-8. The predominant cellular fatty acids were iso-C15:0, iso-C16:0 and iso-C17:1 ω9c. The complete genome sequence of strain 5-21aT revealed that the genome size was 4 155 451 bp long and the G+C content was 67.87 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between strain 5-21aT and its most closely phylogenetic relative L. soli DCY21T were 88.8 and 36.5%, respectively. Based on genomic, chemotaxonomic, phenotypic and phylogenetic data, strain 5-21aT represents a novel species in the genus Lysobacter, for which the name Lyobacter auxotrophicus sp. nov. is proposed. The type strain is 5-21aT (=NBRC 115507T=LMG 32660T).