Resistance to Bacteriophage 6 by Pseudomonas phaseolicola

Publisher Website
Google Scholar
Abstract
Resistance to bacteriophage .vphi.6 by P. phaseolicola [syringae] HB10Y occurred at a frequency of about 1 in 120,000 cells. Statistical analysis by the fluctuation and re-spreading tests indicated that the majority of .vphi.6R [.vphi. resistant] bacteria resulted from random mutation rather than from contact with the phage. Exposing the bacteria to heated .vphi.6 (50.degree. C for 1 min) or .vphi.6 nucleocapsid (virus minus the lipid envelope) prior to testing for resistance increased the frequency 2- to 3-fold; .vphi.6 ds[double-stranded]RNA, unheated .vphi.6, or heated .vphi.91 did not have this effect. Nine resistant variants were selected for further characterization. When DNA isolated from the variants was subjected to agarose gel electrophoresis, 7 of the 9 strains had 2 plasmid DNA bands typical of Hb10Y; the remaining 2 strains had 3 plasmid bands. .vphi.6 attached to the pili of 6 of the 9 variants; 4 of the variants actually had higher adsorption rate constants than HB10Y. Culture supernatants from the .vphi.R strains did not inactivate .vphi.6. One of the resistant strains, D5, produced large amounts of infectious .vphi.6 particles during its exponential phase of growth without a significant effect on its growth rate. Treatment of D5 with .vphi.6 antiserum resulted in the loss of .vphi.6 production, but unlike typical carrier-state cells, D5 retained its resistance of .vphi.6. Apparently resistance to .vphi.6, although occurring at a relatively high frequency, is not due to 1 common event, such as loss of a plasmid and/or attachment sites.