Mating due to loss of surface exclusion as a cause for thermosensitive growth of bacteria containing the Rtsl plasmid.
At 25 degrees C, Rtsl+ bacteria grow to about 5 X 10(9) bacterial/ml before leveling off, whereas at 42 degrees C they grow from 2.6 X 10(8) bacteria/ml for only 2-3 generations after temperature shift before the growth is inhibited with a zig-zag pattern at the plateau. When diluted, Rtsl+ bacteria grow rapidly at 42 degrees C, until the concentration reaches as high as the undiluted 42 degrees C culture when growth measured by colony counts stops and the zig-zag pattern again appears. This density-dependent growth inhibition is not due to the presence of stable growth inhibitor(s). Mating experiments show that at 42 degrees C, Rtsl+ bacteria retain good donor ability; at the same time, they become good recipients in mating with Hfr (Rtsl) bacteria. SDS-PAGE reveals that membranes are altered at 42 degrees C. Examination of DNA synthesis indicates that chromosomal DNA is synthesized at both 25 degrees C and 42 degrees C at high bacterial concentration, but that of the Rtsl plasmid is slowed down at 42 degrees C. The labeling experiments suggest that in 2 h there are 2 rounds of plasmid replication at 25 degrees C, 3.5 rounds at 42 degrees C when bacteria are diluted, and 0.6 rounds at 42 degrees C when bacteria are not diluted. These results suggest that the growth inhibition of Rtsl+ bacteria at 42 degrees C is probably the consequence of mating initiated due to loss of surface exclusion.
D002499:Centrifugation, Density Gradient; D003227:Conjugation, Genetic; D004269:DNA, Bacterial / Q000096:biosynthesis; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development; D006358:Hot Temperature; D008565:Membrane Proteins / Q000235:genetics; D010641:Phenotype; D011815:R Factors
D004269:DNA, Bacterial; D008565:Membrane Proteins