Sexuality in a natural population of bacteria--Bacillus subtilis challenges the clonal paradigm.

Reproduction by binary fission necessarily establishes a clonal genotypic structure in bacterial populations unless a high rate of genetic recombination opposes it. Several genetic properties were examined for a wild population of Bacillus subtilis in the Sonoran Desert of Arizona to assess the extent of recombination in a natural population. These properties included allozyme variation revealed by multilocus enzyme electrophoresis, phage and antibiotic resistance, and restriction fragment length polymorphism with Southern hybridization. Evidence of extensive genetic recombination was found along with evidence of modest clonal structure. Recombination must be frequent relative to binary fission in this population. This mixed population structure provides broader options for bacterial evolution than would a purely clonal structure.