Methylophilus glucosoxydans sp. nov., a restricted facultative methylotroph from rice rhizosphere

Abstract

Two restricted facultatively methylotrophic strains, designed BT and P, were isolated from rice roots. The isolates were strictly aerobic, Gram-negative, asporogenous, mesophilic, neutrophilic, motile rods that multiplied by binary fission and were able to synthesize indole-3-acetate. The cellular fatty acid profiles of the two strains were dominated by C16 : 0, C16 : 1ω7c and C16 : 0 2-OH. The major ubiquinone was Q-8. The predominant phospholipids were phosphatidylethanolamine and phosphatidylglycerol. Cardiolipin (diphosphatidylglycerol) was absent. The two strains assimilated methanol carbon at the level of formaldehyde via the ribulose monophosphate cycle (2-keto-3-deoxy-6-phosphogluconate variant). They lacked α-ketoglutarate dehydrogenase and glutamate dehydrogenase. They assimilated ammonium via the glutamate cycle enzymes glutamine synthetase and glutamate synthase. The DNA G+C contents of strains BT and P were 52.5 and 51.5 mol% (T m), respectively. The level of DNA–DNA reassociation between these strains was 78 %, indicating that they belong to one species. Phylogenetic analysis of strain BT based on 16S rRNA and methanol dehydrogenase (mxaF) gene sequences showed a high level of similarity to members of the genus Methylophilus. As the two isolates were clearly distinct from all recognized members of the genus Methylophilus based on phenotypic data and levels of DNA–DNA relatedness (30–46 %), they are considered to represent a novel species, for which the name Methylophilus glucosoxydans sp. nov. is proposed; the type strain is BT ( = VKM B-1607T = CCUG 59685T = DSM 5898T).