Characterization of Methanococcus maripaludis sp. nov., a new methanogen isolated from salt marsh sediment

Abstract

A predominant methanogenic bacterium was isolated from salt-marsh sediment near Pawley's Island, South Carolina. A habitat-simulating medium with H₂:CO₂ as substrate was used for enrichment and isolation. The methanogen is strictly anaerobic, weakly-motile, non-sporeforming, Gram negative, and a pleomorphic coccoid-rod averaging 1.2 by 1.6 μm. Colonies are circular, translucent, pale yellow, and have a smooth surface and an entire edge. The organism is a mesophile, growing between 18 and 47°C, with an optimum near 38°C. The pH optimum for growth is 6.8–7.2, and only formate or a mixture of H₂ plus CO₂ serve as substrates. Seawater (20–70% v/v) is required, but it can be replaced by 15 mM, or greater, magnesium. Optimal growth occurs with 110 mM sodium. Growth rate is stimulated by selenium (10 μM) but organic compounds (acetate, vitamins, amino acids) are neither stimulatory nor required. The methanogen grows well in autotrophic medium with a doubling time of about 2h. Cells are fragile, are lysed by aqueous solutions of low osmolality and by detergents, and the lack muramic acid. The cell wall is a single electron dense layer. The DNA base composition is 33 mol % guanine plus cytosine. Antigenic relationship of cells and the 16S ribosomal RNA catalog indicate that the salt marsh methanogen is a unique species of Methanococcus, for which we propose the name Methanococcus maripaludis sp. nov.