INFLUENCE OF GENETIC-MARKERS AND OF THE FUSING AGENT POLYETHYLENE-GLYCOL ON CHROMOSOMAL GENE-TRANSFER IN SPIROPLASMA-CITRI

Gene transfer-recombination involving three different chromosomal markers (ArsR, VanR, and XylR) and influence of the fusing agent PEG on transfer efficiency were investigated in matings between single-resistant or single and double-resistant strains of Spiroplasma citri. Efficiency and kinetics vary, in S. citri, with the markers involved in the crosses and are not enhanced by the membrane fusion effect of PEG. These features allow one to distinguish the chromosomal gene transfer in S. citri from the closely related transfer by protoplast fusion in Gram-positive bacteria. However, the results may be explained by a spontaneous high frequency of the membrane fusion events of S. citri cells and the existence of variations in the recombination frequency of the markers. Indeed, in S. citri, the formation of the heterozygotic polyploid structure formed after membrane fusion may be considered as a nonlimiting step of the mechanism and allows one, accordingly, to point out differences in recombination frequencies of the markers. © 1990 Springer-Verlag New York Inc.