Population Dynamics of Rhizobium leguminosarum Tn5 Mutants with Altered Cell Surface Properties Introduced into Sterile and Nonsterile Soils

ABSTRACT

The influence of cell surface properties on attachment to soil particles and on population dynamics of introduced bacteria was studied in sterilized and nonsterilized loamy sand and silt loam. Rhizobium leguminosarum RBL5523 and three Tn5 mutants (RBL5762, RBL5810, and RBL5811) with altered cell surface properties were used. Cellulose fibrils were not produced by RBL5762. Both RBL5810 and RBL5811 produced 80 to 90% less soluble exopolysaccharides and RBL5811 had, in addition, an altered lipopolysaccharide composition. In sterilized soil the total number of cells as well as the number of particle-associated cells of RBL5523 and RBL5810 were, in general, higher as compared with cell numbers of RBL5762 and RBL5811. Differences between strains in percentage of particle-associated cells in sterilized soil were only found at high inoculum densities, when populations increased little. In the nonsterilized silt loam, final population sizes, as well as numbers of particle-associated cells, of the parental strain (RBL5523) were higher than those of strains with altered cell surface properties after 56 and 112 days of incubation. But in general, differences in survival among the strains were not very marked. The importance of association with soil particles or aggregates for the survival of introduced cells was affirmed by the pronounced increase of the percentage of particle-associated cells during incubation in nonsterilized as well as sterilized soil. However, no clear relation among altered cell surface properties, particle association, and survival was found.