Methylothermus thermalis

Cell morphology of strain MYHTT. (a) Phase-contrast micrograph. (b) Ultrathin section of cell showing cell wall structure (CW) and the intracytoplasmic membrane (ICM) arrangement. (c) Highly magnified, negative-contrast image showing the surface layer with linear (p2) symmetry. Bars, 1 mm (a), 0?5 mm (b) and 0?1 mm (c).From http://ijs.sgmjournals.org/cgi/content/abstract/55/5/1877 Jun Tsubota et al. 2005.

Classification

Bacteria; Proteobacteria; Gammaproteobacteria; Methylococcales; Methylococcaceae

Species

Methylothermus thermalis

NCBI: Taxonomy

Description and Significance

This organism was found in a Japanese hot spring (location not specified). Methylothermus thermalis grew as small (1–2 mm in diameter), white, semi-transparent colonies with an entire edge and smooth surface were obsevered after 1-2 weeks. Older colonies (1 month) were light brown and more rigid. Unlike most discovered methanotrophs, this species can survive at high temperatures while metabolizing methane and methanol. It is classified as a type I thermophilic methanotroph, which uses the RuMP pathway instead of the type II serine pathway.

Phylogenetic tree showing the relationship of the 16S rRNA gene sequence of strain MYHTT to those of some methanotrophs in the class ‘Gammaproteobacteria’. The sequences were aligned using the CLUSTAL program; 1200 bp were used for the tree construction with the TREECON program (version 1.3b) using the neighbourjoining algorithm. Bootstrap values less than 50% are not shown. The tree was rooted using Escherichia coli. Bar, 0.1 substitutions per base position. GenBank accession numbers are given in parentheses. From http://ijs.sgmjournals.org/cgi/content/abstract/55/5/1877 Jun Tsubota et al. 2005.

Genome Structure

The nifH gene, which codes for nitrogenase reductase, was not detected with PCR analysis. Since nitrogenase reductase is component II of the nitrogenase enzyme complex, M. thermalis cannot fix its own atmospheric nitrogen. Also, the mmoX gene was not detected by PCR using the respective primer set that is universal for the known mmoX genes of methanotrophs. The genome of this microorganism has yet to be sequenced and as a consequence the size and characteristics are not well known.

The G+C DNA content of 62.5 mol% for M. thermalis is close to that found for type II and type X methanotrophs. The 16S rRNA gene database search showed that this organism is closely related to the thermophilic methanotroph Methylothermus (91% sequence identity, based on the comparison of 1442 available bases) and the novel halophilic methanotroph Methylohalobius crimeensis (90 %). The other closest neighbors were the moderately thermophilic methanotrophs Methylococcus thermophilus and Methylocaldum szegediense, and the thermotolerant Methylococcus capsulatus Bath (about 85–86% 16S rRNA gene sequence identity). Phylogenetic analysis based on partial pmoA gene sequences confirmed the clustering of M. thermalis with Methylothermus strain HB (90% nucleotide sequence identity and 98% derived amino acid sequence identity) and Methylohalobius crimeensis (83 and 92 %, respectively). In contrast, the partial pmoA gene sequence of M. thermalis exhibited no more than 77% identity to the corresponding gene fragments of Methylocaldum szegediense, Methylocaldum gracile and Methylococcus capsulatus Bath. So far, information on true thermophilic methanotrophs is limited, with only a brief and non-formal taxonomic description of Methylothermus strain HB.

Pathways for the oxidation of methane and assimilation of formaldehyde. Abbreviations: CytC, cytochrome c; FADH, formaldehyde dehydrogenase; FDH,formate dehydrogenase. From https://www.ocean.udel.edu/cms/thanson/TH-MicroRev.pdf Hanson R and Hanson T, 1996.].

RuMP pathway for formaldehyde fixation. The reactions catalyzed by the unique enzymes of this pathway, hexulose-6-phosphate synthase and hexulosephosphate isomerase, are indicated. From https://www.ocean.udel.edu/cms/thanson/TH-MicroRev.pdf Hanson R and Hanson T, 1996.].

Cell Structure, Metabolism and Life Cycle

The cells grown in liquid culture were mostly represented by coccoids of 0.6–0.8 mm in diameter (Fig. 1a). In contrast, the majority of cells grown on solid medium appeared as short rods, slightly varying in size (0.6–0.8 x 1.0–1.2 mm). The cells were non-motile, and multiplied by normal cell division. The cells showed a typical Gram-negative structure of the cell wall, and the presence of type I intracytoplasmic membrane (ICM) arranged as stacks of vesicular disks (Fig. 1b) that completely filled the cytoplasmic space. Glycogen inclusions and poly-beta-hydroxybutyrate granules usually present in mesophilic methanotrophs were not observed.

Methylothermus thermalis requires methane or methanol as a carbon and energy source to growth. This species can use nitrate, ammonia, urea, tryptophan,lysine, glutamate, formamide and Triss as nitrogen sources, but no growth was obsevered without one of these sources. The cells grew on methane or methanol at 37–67 6C, and optimally at 57–59 6C. Interesting features of cell structure; how it gains energy; what important molecules it produces.

Ecology

biogeochemical significance; This species is a methanotroph and therefore it helps to sequester methane from the atmosphere.

Characteristics of type I, type II, and type X methanotrophs; phylogenetic signature probes 1041 and 1035 will not hyidize with 16S rRNAs from members of the genus Methylomonas. Probes MM650 and MM850 have been employed to detect some species in this genus. From https://www.ocean.udel.edu/cms/thanson/TH-MicroRev.pdf Hanson R and Hanson T, 1996.].

References

1: Carmen Quinto, Humberto De La Vega, Margarita Flores, Jan Leemans, Miguel Angel Cevalios, Marco Aurelio Pardo, Ricardo Azpiroz, Maria De Lourdes Girard, Edmundo Calva, and Rafael Palacios. 1985. "Nitrogenase reductase: A functional multigene family in Rhizobium phaseoli". Proc. Nail. Acad. Sci. USA Vol. 82, pp. 1170-1174.

2: Jun Tsubota, Bulat Ts. Eshinimaev, Valentina N. Khmelenina and Yuri A. Trotsenko. 2005. "Methylothermus thermalis gen. nov., sp. nov.,a novel moderately thermophilic obligate methanotroph from a hot spring in Japan". International Journal of Systematic and Evolutionary Microbiology. 55, 1877–1884.

3: Richard Hanson and Thomas Hanson. 1996. "Methanotrophic Bacteria". American Society for Microbiology, Vol. 60, No. 2.

Author

Page authored by Anthony Heidt and James Goodrow Jr., student of Prof. Jay Lennon at Michigan State University.