title: Genome sequence of Symbiobacterium thermophilum, an uncultivable bacterium that depends on microbial commensalism.
abstract: Symbiobacterium thermophilum is an uncultivable bacterium isolated from compost that depends on microbial commensalism. The 16S ribosomal DNA-based phylogeny suggests that this bacterium belongs to an unknown taxon in the Gram-positive bacterial cluster. Here, we describe the 3.57 Mb genome sequence of S.thermophilum. The genome consists of 3338 protein-coding sequences, out of which 2082 have functional assignments. Despite the high G + C content (68.7%), the genome is closest to that of Firmicutes, a phylum consisting of low G + C Gram-positive bacteria. This provides evidence for the presence of an undefined category in the Gram-positive bacterial group. The presence of both spo and related genes and microscopic observation indicate that S.thermophilum is the first high G + C organism that forms endospores. The S.thermophilum genome is also characterized by the widespread insertion of class C group II introns, which are oriented in the same direction as chromosomal replication. The genome has many membrane transporters, a number of which are involved in the uptake of peptides and amino acids. The genes involved in primary metabolism are largely identified, except those that code several biosynthetic enzymes and carbonic anhydrase. The organism also has a variety of respiratory systems including Nap nitrate reductase, which has been found only in Gram-negative bacteria. Overall, these features suggest that S.thermophilum is adaptable to and thus lives in various environments, such that its growth requirement could be a substance or a physiological condition that is generally available in the natural environment rather than a highly specific substance that is present only in a limited niche. The genomic information from S.thermophilum offers new insights into microbial diversity and evolutionary sciences, and provides a framework for characterizing the molecular basis underlying microbial commensalism.
authors.affiliation: Life Science Research Center, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-8510, Japan. ueda@brs.nihon-u.ac.jp
authors.forename: Kenji
authors.initials: K
authors.lastname: Ueda
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yamashita
authors.forename: Jun
authors.initials: J
authors.lastname: Ishikawa
authors.forename: Masafumi
authors.initials: M
authors.lastname: Shimada
authors.forename: Tomo-o
authors.initials: TO
authors.lastname: Watsuji
authors.forename: Kohji
authors.initials: K
authors.lastname: Morimura
authors.forename: Haruo
authors.initials: H
authors.lastname: Ikeda
authors.forename: Masahira
authors.initials: M
authors.lastname: Hattori
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Beppu
mesh_terms: D039903:Actinobacteria / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D000332:Aerobiosis; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D004260:DNA Repair; D004261:DNA Replication; D020862:GC Rich Sequence; D022761:Gene Transfer, Horizontal; D016680:Genome, Bacterial; D020071:Interspersed Repetitive Sequences; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D011995:Recombination, Genetic; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins