Characterization of the first rice paddy cluster I isolate, Methyloterricola oryzae gen. nov., sp nov and amended description of Methylomagnum ishizawai

A Three gammaproteobacterial methanotrophic strains (73a(T), 175 and 114) were isolated from stems of rice plants. All strains are Gram-negative, motile and grow on methane or methanol as sole carbon sources. They oxidize methane using the particulate methane monooxygenase. Strains 114 and 175 possess additionally a soluble methane monooxygenase. All strains contain significant amounts of the cellular fatty acids C-16 : 0, C-16 : 1 omega 6c and C-16 : 1 omega 7c, typical for type Ib methanotrophs. Characteristic for strains 114 and 175 are high amounts of C-14 : 0 and C-16 : 1 omega 6c, while strain 73a(T) contains high quantities of C-16 : 1 omega 5c. 16S rRNA gene sequence analyses showed that strains 114 and 175 are most closely related to Methylomagnum ishizawai (>= 99.6% sequence identity). Strain 73a(T) is representing a new genus within the family Methylococcaceae, most closely related to Methylococcus capsulatus (94.3% sequence identity). Phylogenetic analysis of the PmoA sequence indicates that strain 73a(T) represents rice paddy cluster I (RPCI), which has almost exclusively been detected in rice ecosystems. The G+C content of strain 73a(T) is 61.0 mol%, while strains 114 and 175 have a G+C content of 63.3 mol%. Strain 73a(T) (= LMG 29185(T), = VKM B-2986(T)) represents the type strain of a novel species and genus, for which the name Methyloterricola oryzae gen. nov., sp. nov. is proposed and a description is provided. Strains 175 (= LMG 28717, VKM B-2989) and 114 are members of the species Methylomagnum ishizawai. This genus was so far only represented by one isolate, so an amended description of the species is given.