Symbiobacterium thermophilum

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A Microbial Biorealm page on the genus Symbiobacterium thermophilum


Higher order taxa

Bacteria; Firmicutes; Lactobacillales; Symbiobacterium Domain; Phylum; Class; Order; family [Others may be used. Use NCBI link to find]


NCBI: Taxonomy

Genus species Symbiobacterium thermophilum

Description and significance

Symbiobacterium thermophilum is a Gram-negative and tryptophanase-positive thermophilic bacterium found in a commensal submerged culture that was derived from compost. This bacterium is characterized by a marked growth dependence on microbial commensalism; it does not grow by itself under standard culture conditions; however, when cocultured with Bacillus sp. strain S, it propagates up to 5 × 108 cells/ml (5). Molecular phylogeny using the 16S ribosomal DNA (rDNA) sequence has indicated that S.thermophilum belongs to an unknown taxonomic group in the Gram-positive bacterial cluster (1). The current 16S rDNA database content suggests that the presence of this bacterium and related organisms is still poorly recognized, probably due to the technical problems involved in its isolation. Meanwhile, our ecological study has revealed the potential phylogenetic diversity and the wide distribution of Symbiobacterium and related bacteria in the natural environment.

Genome structure

The S. thermophilum genome is 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 membranes 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 (1). 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 (5). The random sequencing strategy indicated that S.thermophilum has a circular chromosome consisting of 3566135 bp with 68.7% G + C and no extrachromosomal element. The GC skew clearly indicated the direction of replication and the position of the replication origin (oriC). The oriC contains AT-rich repeated sequences, which probably serve as the binding sites for DnaA encoded immediately downstream from oriC.

Cell structure and metabolism

A whole genome sequencing study uncovered its unusual features, which overall indicate that this bacterium is a member of Firmicutes despite of its high G+C content (68.7%). The genome appeared to retain fully the genes for primary metabolism, except for carbonic anhydrase. Carbon dioxide is a marked inducer of the monogrowth of S.thermophilum, and specultaed that this is die to a loack of carbonic anhydrase. The lines of evidence suggest that S.thermophilum requires additional conditions for full growth, including not only the supply of an unknown positive factor but also the elimination of oxygen and self-growth inhibitory substances(3).


Symbiobacterium thermophilum is adaptable to and thus lives in various enviornments, 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 subsance that is present only in a limited niche(1). Mixed cultures of thermophiles containing Symbiobacterium species are frequently obtained from compost, soil, animal feces, and contents in the intestinal tracts, as well as feeds(2).


Symbiobacterium thermophilum is non-pathogenic.

Current Research

There is current research on the structure of the Dopamine D2-like receptor binding sites. There is also research on Archael and bacterial homologs of Dopamine transporters as models for mammalian neurotransmitter transporters. A project supported by NIMH focuses on identifying the dimer interface of the dopamine D2 receptor and other G-protein-coupled receptors and on characterizing conformational changes at the dimer interface and their role in receptor function. This project also aims to demonstrate the role of the second extracellular loop in ligand binding and selectivity(4).


Beppu, T., Hattori, M., Ikeda, H., Ishikawa, J., Morimura, K., Shimada, M., Ueda, K., Watsuji, T., Yamashita, A. "Genome sequence of Symbiobacterium thermophilum, an uncultivable bacterium that depends on microbial commensalism". "Oxford Journals". 2004. Volume 32, Number 16. Pp. 4397-4944.

Ueda, K., Ohno, M., Yamamoto, K., Nara, H., Mori, Y., Shimada, M., Hayashi, M., Oida, H., Terashima, Y., Nagata, M., and Beppu, T. "Distribution and Diversity of Symbiotic Thermophiles, Symbiobacterium thermophilum and Related Bacteria, in Natural Environments". "Applied and Environmental Microbiology". September 2001. Volume 67, No. 9.

Ueda, K., and Beppu, T. "Lessons From Studies of Symbiobacterium thermophilum, a Unique Syntrophic Bacterium". "Bioscience, Biotechnology, and Biochemistry". 2007. Volume 71, No. 5. Pp. 1115-1121.

Edited by student of Stephanie Miller, Northeast State Technical Community College, Blountville, Tennessee