These experiments will examine the evolutionary dynamics of genetically variable Bacillus subtilis populations in soil microcosms and examine the biological and physical factors which facilitate recombination. The experiments will be performed during a sabbatical leave in the laboratory of Dr.C.A. Istock at the University of Arizona. These questions will be addressed: 1) Do natural genotypes of B. subtilis differ in fitness? 2) Do relative fitnesses of genotypes change as a function of biotic or physical environmental conditions? 3) Is recombination frequency correlated with specific habitat conditions? 4) Are genetically variable soil populations of B. subtilis more resistant to bacteriophage predators than are monomorphic cultures? 5) Is there a genetic cost to sexual reproduction in B. subtilis? The basic procedure in these experiments will be to 1) inoculate soil microcosms with heat-shock spores or vegetative cells of one or more isogenic strains of B. subtilis, 2) sample these populations at intervals, 3) estimate the density of vegetative cells and spores, and 4) determine genotype/recombination frequencies by protein, antibiotic resistance, colony morph, and DNA restriction fragment polymorphisms. Additionally, to address question 5 the PI will transform competent B. subtilis in broth culture using prepared donor DNA. These results will illuminate the relative costs, benefits, and ecological and evolutionary consequences of genetic recombination and diversity in a species with a primitively asexual breeding system.
