QUANTITATIVE ASPECTS OF TRANSFORMATION OF VIRULENCE IN AGROBACTERIUM TUMEFACIENS

Abstract

Transformation of virulence in A. tumefaciens was studied by means of a quantitative bioassay for grown-gall tumor formation. The transforming principle is not a bacter- iophage, but a desoxyribonucleic acid present in filtrates of growing donor cultures. Only certain donor and recipient combinations are effective in transformation. Virulence of an altered population increases to a maximum with successive periods of active growth and can be boosted by additional exposure to transforming principle. Over 30% of the isolates of a stabilized, altered population possess grades of virulence significantly greater than any isolates from the unaltered, recipient population. Acquisition of virulence appears to be host or host-range specific. It is proposed that virulence is con trolled by multiple loci regulating the synthesis of a tumor- inducing principle effective in plants of a given host range. Grades of virulence in a given host-range may ultimately be controlled by multiple alleles at each host range locus.