Isolation of uncultivated anaerobic thermophiles from compost by supplementing cell extract of Geobacillus toebii in enrichment culture medium

Several researchers have reported that microorganisms can be cultivated only in the presence of other microorganisms. We suggest that a portion of uncultivated microorganisms might be cultivated in the presence of cellular components released from bacteria in their natural environments. In this study, the cell extract of Geobacillus toebii was used to enrich uncultivated thermophiles from compost. In the process of enrichment cultures, cell extract supplementation apparently changed the community composition. This change was monitored by PCR-DGGE targeting 16S rRNA gene. Five novel groups of microorganisms (similarity of 16S rRNA gene to the closest relative <96%) were specifically isolated from enrichment cultures by using cell extract-supplemented culture media. Their growth was found to be dependent on the addition of extract of G. toebii. Putting these findings together, we suggest that the extracts of bacteria could be one of the growth factors in the thermal ecosystem with a possibility of extending other ecological niches.