Isolation and Biodiversity of Hitherto Undescribed Soil Bacteria Related to Bacillus niacini

The hitherto largely not described phylogenetic neighborhood of Bacillus niacini has been explored by a comprehensive cultivation experiment and genomic variety studies. Previous culture-independent studies demonstrated that ~15% of all Bacillus 16S rDNA directly extracted from soils worldwide was affiliated to B. niacini. Seven different media were inoculated with soil suspensions in serial dilutions and incubated at different temperatures. Then, bacterial colonies were picked and analyzed by sequencing. A mineral medium with acetate as carbon source yielded a B. niacini rate of >3% of all picked colonies. Other media were less efficient but also successful. Applying this culturing approach, we succeeded in obtaining 64 isolates from different Dutch soils. The isolates turned out to be diverse, although closely related to B. niacini as revealed by 16S rDNA sequencing. Close matches with environmental clones were also found, thus demonstrating much more diversity beyond previously known 16S rDNA sequences. The rep-PCR fingerprinting method revealed a high genomic variety, redundancy could not be observed among our isolates. Hence, the hitherto neglected B. niacini lineage, apparently among the most abundant soil Bacillus, was accessible to our cultivation approach.