Cultivatable microbial biodiversity: gnawing at the Gordian knot

Rapid and inexpensive sorting of bacterial isolates may be achieved using F ourier transform infrared spectroscopy (FT-IR), a method that has hitherto been applied to identification and classification. The comprehensive charac terization of environmental samples requires the isolation of large numbers of isolates using different growth media and growth conditions. In such ca ses, sorting the isolates is critical before isolates are subjected to more detailed studies. Using FT-IR, isolates are grown under standardized condi tions, and 100 strains can be tested within less than 8 h. Chemotaxonomic a nd molecular characterization of members of clusters emerging from FT-IR an alysis either at a level of spectral distance values below 20-30 (analysis of region 600-800 cm(-1), average linkage algorithm) or at spectral heterog eneity values below 75 (regions 1200-900, 3000-2798 and 901-698, scaling to first region, Ward's algorithm) reveals great similarities in fatty acids and 16S rDNA sequences. As judged from riboprinting analyses and fatty acid analyses, FT-IR analysis is able to unravel intraspecific subclustering. T he example used in this study of 100 isolates from a mat system, Lake Fryxe ll, Dry Valleys, Antarctica, selected from a larger number of isolates, pic ked mainly on the basis of colony pigmentation and form, reveals the utilit y of the method for identifying the number of putative species quickly. The method described is able to select strains rapidly that represent clusters at the specific and intraspecific level for subsequent characterization.