Distribution and Diversity of Symbiotic Thermophiles, Symbiobacterium thermophilum and Related Bacteria, in Natural Environments

Abstract

Symbiobacterium thermophilum is a tryptophanase-positive thermophile which shows normal growth only in coculture with its supporting bacteria. Analysis of the 16S rRNA gene (rDNA) indicated that the bacterium belongs to a novel phylogenetic branch at the outermost position of the gram-positive bacterial group without clustering to any other known genus. Here we describe the distribution and diversity of S. thermophilum and related bacteria in the environment. Thermostable tryptophanase activity and amplification of the specific 16S rDNA fragment were effectively employed to detect the presence of Symbiobacterium. Enrichment with kanamycin raised detection sensitivity. Mixed cultures of thermophiles containing Symbiobacterium species were frequently obtained from compost, soil, animal feces, and contents in the intestinal tracts, as well as feeds. Phylogenetic analysis and denaturing gradient gel electrophoresis of the specific 16S rDNA amplicons revealed a diversity of this group of bacteria in the environment.

Lessons from Studies ofSymbiobacteriumthermophilum, a Unique Syntrophic Bacterium

“…Compost samples collected from various sites in Japan contained Symbiobacterium at a remarkably high frequency. 9) We also found that feces and feeds of domestic animals were good isolation sources of this kind of bacterium. Further, we examined various feed ingredients and discovered that oyster shell included in bird feed was a frequent isolation source.…”

“…8) Hence, we developed a method based on the PCR technique using internal sequences of the 16S rRNA gene and tnaT as primers. PCR using the 16S rRNA gene primers was used in an ecological detection study of S. thermophilum and relatives, 9) and the one with the primers for tnaT was used in specific quantification of the cell of S. thermophilum.…”

Genome Update: DNA repeats in bacterial genomes

“…The list is shown in Table 1 and represents a wide range of organisms, with three of the four organisms having close relatives that have already been sequenced: the saprophytic soil bacterium Bacillus licheniformis, which is a close cousin of Bacillus subtilis; Yersinia pseudotuberculosis, which is thought to represent the species from which Yersinia pestis originated; the spirochaete Borrelia garinii; and the compost bacterium Symbiobacterium thermophilum, which depends on the presence of other Bacillus bacteria for growth (Ueda et al, 2001). At the time of writing, reports on the Bacillus licheniformis and Y. pseudotuberculosis genomes have been published, which will be briefly discussed below.…”

Identification of Indole Derivatives as Self-Growth Inhibitors of Symbiobacterium thermophilum , a Unique Bacterium Whose Growth Depends on Coculture with a Bacillus sp

“…S. thermophilum exhibits a number of genetic features associated with Firmicutes (low-GϩC, gram-positive bacteria represented by Bacillus and Clostridium), despite its high GϩC content (68.5%). This unusual property has now become a new topic in bacterial systematics (2,4) and suggests that this kind of bacterium has been left uncharacterized due to its "unculturable nature," despite its wide distribution in the natural environment (20). We are interested in the fundamental details of the syntrophic feature of S. thermophilum and expect that this information will provide us with new knowledge regarding not only the microbial physiology but also the issue of unculturability of environmental microorganisms.…”