Description of ‘Candidatus Methylocucumis oryzae’, a novel Type I methanotroph with large cells and pale pink colour, isolated from an Indian rice field

Abstract

An elliptical to cucumber-shaped methanotroph with large cells was isolated from a rice rhizosphere in Western India. Strain Sn10-6 is one of the first methanotrophs to be isolated from Indian rice fields. Cells of Sn10-6 are Gram-negative, motile, large in size (3–6 µm × 1.5–2 µm) and contain intracellular cytoplasmic membrane stacks. Colonies of Sn10-6 and liquid cultures have a pale pink colour. Strain Sn10-6 was initially isolated under micro-oxic conditions but later adapted to grow under fully oxic conditions. The major fatty acids present were identified as C16:1ω6c, C16:1ω7c and C16:0 and ubiquinone was found to be the major quinone. The 16S rRNA gene sequence of strain Sn10-6 displays high similarity to the genes of Methylovulum psychrotolerans Sph1T (93.6%) followed by Methylosarcina fibrata AML-C10T (93.5%) and about 90–93% similarity to the genes of known species of Type I methanotrophic genera from the family Methylococcaceae. The draft genome information indicated that the G + C content of strain Sn10-6 is 43.9 mol%. Phylogenetic trees using 16S rRNA gene and the particulate methane mono-oxygenase sequences unequivocally placed Sn10-6 close to the genus Methylovulum. Based on the 16S rRNA gene differences, morphological characters and draft genome information, strain Sn10-6 (=MCC 3492 =KCTC 15683) is described here as the type strain of a novel species within a new genus, ‘Candidatus Methylocucumis oryzae’.