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

Abstract

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.

Genetic structure of Neisseria gonorrhoeae populations: a non-clonal pathogen

“…Four ETs were each recovered more than nine times and a single genotype, ET 1, accounted for 15.4% of the ETs. In B. subtilis populations the most frequent ET accounted for only 3 YO of the types (Istock et al, 1992).…”

“…However, B. subtilis populations reveal only modest clonal structure (Istock et al, 1992), and a recent statistical analysis of electrophoretic data has revealed that population structures can range from strictly clonal to panmictic (Maynard Smith et al, 1993). An intermediate type of population structure has also been recognized in which the population is panmictic in the long term, but occasionally a highly successful ET arises, which spreads rapidly to produce a degree of linkage disequilibrium in the population.…”

“…Comparison with the population structure of B. subtilis Recent studies of a B. subtilis population taken from a single site have revealed only modest clonal structure (Istock et al, 1992). Statistical tests of association show that 92% of two-locus combinations of N .…”

“…Recent studies suggest that recombination may be more frequent in some bacterial species; tests of linkage disequilibrium reveal that recombination is more frequent in both Bacillus subtilis (Istock et al, 1992) and Rhizobium leguminosarum (Souza et al, 1992) than in E. coli. Our results indicate that N. gonorrhoeae, unlike all pathogens so far examined, has a non-clonal population structure, implying extensive recombination in nature.…”

The potential for intraspecific horizontal gene exchange by natural genetic transformation: sexual isolation among genomovars of Pseudomonas stutzeri The EMBL accession numbers for the sequences reported in this paper are given in Methods.

“…with pathogens like Helicobacter pylori, Neisseria gonorrhoeae, Neisseria meningitidis and Streptococcus pneumoniae, and saprophytic bacteria including Bacillus subtilis and Burkholderia cepacia on the grounds of multilocus enzyme electrophoresis or multilocus restriction typing analyses (Duncan et al, 1994 ;Go et al, 1996 ;Haubold et al, 1998 ;Istock et al, 1992 ;Maynard Smith et al, 1993 ;Mu$ ller-Graf et al, 1999 ;Wise et al, 1995). Genetic diversity created by recombination may help adapt these organisms to adverse environmental conditions or help them overcome a host's defence mechanisms (Robertson & Meyer, 1992).…”