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Methanospirillum hungatei is a mesophilic and hydrogenotrophic methanogen. Its cells are spiral shaped (curved rods, Fig. 1) and Gram-negative, and generally occur in filaments up to 100 mm in length. This strain, first isolated from wastewater sludge (Ferry et. al. 1974), is widely distributed in varied natural habitats (Liu and Whitman, 2008; Lino et al., 2010). Optimum growth conditions include a temperature range of 30-37 °C and a pH range of 6.6-7.4 (Ferry et al., 1974).
The type strain of M. hungatei is strain JF-1, synonymous with DSM 864, ATCC 27890, and JCM 10133. The JF-1 genome is 3.54 Million bp long and contains approximately 3294 predicted genes (NCBI RefSeq Accession: NC_007796). The guanine and cytosine content is 45% for this organism (Ferry et. al. 1974).
M. hungatei produces methane by growing on CO2-H2 or formate. Acetate that can be utilized as a carbon source (Ekiel et al. 1983), acts as a chemotactic stimulator to this strain (Migas et al., 1989). M. hungatei serves an important role as the terminal member in syntrophic associations facilitating growth on propionate with Syntrophobacter spp. and on lactate and other organic substrates with Desulfovibrio spp. in absence of sulfate (Boone and Bryant, 1980; Wallrabenstein et al., 1994). Thus M. hungatei is a keystone species in carbon cycling and biodegradation of organic substrates both in sewage treatment facilities and in natural ecosystems. M. hungatei has been recently confirmed as an important mercury methylator converting less toxic inorganic mercury into the neurotoxicant methylmercury under mineral-limited anaerobic conditions (Yu et al., 2013), consistent with the presence of putative Hg methylation genes in its genome (Parks et al., 2013).