Joo-Han Gwak

Strain 16-5 T , a mesophilic methanotroph of the genus Methylococcus , was isolated from rice field soil sampled in Chungcheong Province, Republic of Korea. Strain 16-5 T had both particulate and soluble methane monooxygenases and could only grow on methane and methanol as electron donors. Strain 16-5 T cells are Gram-negative, white to light tan in color, non-motile, non-flagellated, diplococcoid to cocci, and have the typical type I intracytoplasmic membrane system. Strain 16-5 T grew at 18–38 °C (optimum, 27 °C) and at pH 5.0–8.0 (optimum, pH 6.5–7.0). C 16 : 1 ω7 c (38.8%), C 16 : 1 ω 5 c (18.8%), C 16 : 1 ω 6 c (16.8%) and C 16 : 0 (16.9%) were the major fatty acids, and phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and an unidentified phospholipid were the major polar lipids. The main respiratory quinone was methylene-ubiquinone-8. Strain 16-5 T displayed the highest 16S rRNA gene sequence similarities to other taxonomically recognized members of the genus Methylococcus , i.e. Methylococcus capsulatus Texas T (98.62%) and Methylococcus geothermalis IM1 T (98.49 %), which were its closest relatives. It did, however, differ from all other taxonomically described Methylococcus species due to some phenotypic differences, most notably its inability to grow at temperatures above 38 °C, where other Methylococcus species thrive. Its 4.34 Mbp-sized genome has a DNA G+C content of 62.47 mol%, and multiple genome-based properties such as average nucleotide identity and digital DNA-DNA hybridization value distanced it from its closest relatives.