Methylosarcina fibrata gen. nov., sp nov and Methylosarcina quisquiliarum sp nov., novel type I methanotrophs

Two novel species of obligate methane-oxidizing bacteria, isolated from lan dfill soil, were characterized. Both strains were unusual in that some that some members of the population grew in irregularly shaped, refractile cell packets that resembled sarcina-like clusters. Electron microscopy revealed that the cell packets were covered with a slime layer and the cells contai ned many large granular inclusion bodies. The individual cells of each stra in were sometimes motile and had differing morphologies. Isolate AML-C10(T) was always coccoidal in shape, and the cells were covered with extracellul ar fibrils. Isolate AML-D4(T) was pleomorphic, changing from rod to coccal form, sometimes exhibiting an unusual fusiform morphology. AML-D4(T) lacked the extensive fibrillar matrix observed with AML-C10(T). Both strains util ized only methane and methanol as carbon sources. In stationary phase, the cells of each strain swelled in size and formed cysts. Aside from morpholog ical differences, strains could also be distinguished from each other by ce llular protein patterns, as well as by temperature and pH tolerances. 16S r DNA phylogenetic analysis showed that these are type I methanotrophs (famil y: Methylococcaceae) most closely related to the Methylobacter/Methylomicro bium clade, although they form a monophyletic grouping supported by moderat ely high bootstrap values. By 16S rDNA database searches, the most similar species to both isolates were Methylobacter spp. However, partial particula te methane monooxygenase sequence analysis suggested that these bacteria mi ght be more closely related to Methylomicrobium than Methylobacter. Further more, cellular fatty acid profiles of the strains more closely resemble tho se of Methylomicrobium, although the absence of significant levels of 16:1 omega 5c argues for the uniqueness of these two strains. On the basis of th e results described here, it is proposed that a new genus should be created , Methylosarcina gen. nov., harbouring two species, Methylosarcina fibrata sp. nov. (type species) and Methylosarcina quisquiliarum sp, nov. The type strains are AML-C10(T)(= ATCC 700909(T) = DSM 13736(T)) and AML-D4(T)(= ATC C 700908(T) = DSM 13737(T)), respectively.