An enrichment isolation procedure for minor Bacillus populations

In general, spores of B. cereus, B. megaterium, B. Sphaericus and B. subtilis strains germinated uniformly within a short time of incubation in a germination medium. In contrast, spores of B, circulans, B. brevis, B. laterosporus, B. pulvifaciens, B. polymyxa, B. pumilus, B. licheniformis and B. coagulans strains were usually slow and/or uneven germinators under the same conditions of incubation. The former group of Bacillus strains occur frequently in soils as the predominant population and the latter group of Bacillus species are found in many cases as minor populations. The minor populations of Bacillus were isolated with difficulty by the standard dilution-plate technique, but could easily be enriched by treating the soil sample in a germination medium for 2 to 3 hours at 30 to 35 degrees C, followed by heating it at 65 degrees C for 10 minutes ("minor-shifted isolation"). Using this technique, the minor Bacillus strains could be isolated from samples containing 100- to 1,000-fold more of the rapid germinators of Bacillus.