Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2005
Publication Date: 8/5/2005
Citation: Simon, H.M., Jahn, C.E., Bergerud, L.T., Sliwinski, M.K., Weimer, P.J., Willis, D.K. Goodman, R.M. 2005. Cultivation of mesophilic soil crenarchaeotes in enrichments from plant roots. Applied and Environmental Microbiology 71(8):4751-4760. Interpretive Summary: The vast majority of species of microorganisms in nature have not yet been grown in pure culture in the laboratory, making it difficult to understand their properties and the role they may play in the environment. We examined one particular group of microorganisms that are known to be associated with plant roots, but has not been cultivated in the laboratory either as a pure culture or as a mixture of other organisms. Techniques were developed that allowed us to measure the populations of these organisms when present in a complex microbial mixed population. Using these techniques and a combination of feeding with root extracts, and of treatment with antibiotics and cycles of freezing and thawing, we were able to enrich this population to about 40% of the total microbial population, and to increase the total numbers of these cells in cultures. These techniques should allow similar enrichment and characterization of previously undiscovered, difficult-to-culture organisms in other environments, including the intestinal tracts of livestock.
Technical Abstract: Because archaea are generally associated with 'extreme' environments, detection of nonthermophilic members belonging to the archaeal division Crenarchaeota over the last decade was unexpected; equally surprising was their ubiquity and abundance in conventional marine and terrestrial habitats. The metabolic characterization of these nonthermophilic crenarchaeotes has been impeded by their intractability toward isolation and growth in culture. Using a combination of cultivation and molecular phylogenetic techniques (PCR-single-strand conformation polymorphism, fluorescence in situ hybridization, and real-time PCR), we present here evidence that one of the two dominant phylotypes of Crenarchaeota that colonizes the roots of tomato plants grown in soil is selectively enriched in cultures amended with root extract. Our results provide the first evidence for growth of nonthermophilic crenarchaeotes in culture, albeit in mixed enrichments. This work corroborates and extends our recent findings indicating that the diversity of the crenarchaeal soil assemblage is influenced by the rhizosphere and that mesophilic soil crenarchaeotes are found associated with plant roots.