Mutants of nitrogen-fixing rhizospheric bacterium Pseudomonas sp. 418 with loss of the ability to colonize roots

摘要

Mutants of nitrogen-fixing rhizospheric bacterium Pseudomonas sp. 418, which lacked the competitive ability to colonize roots, were induced by random Tn5 mutagenesis. By means of Southern blot analysis,it was shown that single transposon insertions occurred in eight mutants, whereas in two mutants, the Tn5 insertion occurred twice in different DNA regions. Analysis of these mutants revealed the following disturbances of characters having adaptive significance: weakened attachment to the root surface; a defect in chemotaxis; impaired motility as a result of the loss of flagella or nondisjunction of cells after division; and alterations in the synthesis of exopolysaccharides. The effect of Tn5 insertions was, as a rule, pleiotropic, which suggests the coordinated expression of traits essential for the survival of bacterial cells in the root region.