Regulation of polar surface structures in Caulobacter crescentus: pleiotropic mutations affect the coordinate morphogenesis of flagella, pili and phage receptors.

A large number of Caulobacter mutants resistant to DNA or RNA phages were isolated. These phage-resistant mutants exhibited phenotypic variations with respect to cell motility and sensitivity to other phages. The majority of the mutants was resistant to both DNA and RNA phages tested. In addition, these mutants were either motile or non-motile. The analysis of spontaneous revertants from these mutants indicated that a single mutation is involved in these phenotypic variations. Other mutants were resistant to RNA phages and only to a certain DNA phage tested, and were also motile or non-motile. Several temperature-sensitive phage-resistant mutants were also isolated. One of them, CB13 ple-801, exhibited the wild type phenotype when grown at 25 degrees C. However, at a higher temperature (35 degrees C), the mutant cells became non-motile and resistant to both DNA and RNA phages. These phenotypes seem to be attributed to the concommitant loss of flagella, pili and phage receptors. In other respects (cell growth and morphology, and asymmetric stalk formation), CB13 ple-801 was normal at 35 degrees C. The spontaneous revertants from CB13 ple-801 simultaneously regained the wild type phenotypes in all respects. It is suggested that a single mutation pleiotropically affects the formation of flagella, pili and phage receptors.