Methylococcales ord. nov.

Abstract

Morphology varies from rods to cocci. Cells are usually single or diploid, occasionally forming chains and tetrads. Do not form rosettes. If motile, possess single polar flagellum. Gram negative. The majority of species produce a polysaccharide cyst-like resting stage. Cysts may be desiccation resistant or sensitive. Dissimilatory methane oxidation is associated with type I intracytoplasmic membranes, which appear as stacks of vesicular disks derived from convolutions of the cytoplasmic membrane. Catalase and oxidase are usually produced. Strictly aerobic respiratory metabolism with oxygen as the electron acceptor. Obligate utilizers of methane and other C ₁ compounds for carbon and energy. Compounds with carbon-carbon bonds are not utilized. High levels of organic solutes and ammonia ions inhibit growth. C₁ compounds are incorporated by the ribulose monophosphate pathway. The tricarboxylic acid cycle is incomplete, with 2-oxoglutarate dehydrogenase activity absent. Nitrogenase activity may be present. Contain mainly C ₁₆ fatty acids, which are predominantly monounsaturated with several different C_16:1 isomers present. Ubiquinone-8 or 18-methyleneubiquinone-8 are the predominant lipoquinones.