Characterization of cell surface properties in agglutinable and nonagglutinable mutants of Pseudomonas putida

Cells of an aggressive, root-colonizing isolate of Pseudomonas putida are agglutinated by a root surface glycoprotein. The agglutination phenotype in P. putida isolate Corvallis is lacking in mutants (Agg-) derived by Tn5 insertion and chemical mutagenesis. Specific mutation in the aggA locus by Tn5 insertion results in loss of agglutinability that is complemented in trans by a wild-type copy of the P. putida aggA locus. We examined the biochemical bases of agglutination in P. putida by comparing cell surface features in Agg+, Agg- mutants, and a genetically restored aggA mutant. No changes in gross cell surface features involving hydrophobic or hydrophilic binding or net negative charge were observed. Three macromolecular features, pili, flagella, and lipopolysaccharide size, did not differ between Agg+ and Agg- mutants. Protein profiles of cell envelope, periplasmic, and outer membrane preparations revealed pleiotropic effects of mutation in agglutination phenotype including alterations of an outer membrane protein of 47,000 molecular weight and periplasmic proteins of 56,000 and 60,000 molecular weight. The protein alterations seen in the aggA::Tn5 Agg- mutant 5123 reverted to wild-type patterns upon introduction of a wild-type copy of the aggA locus. These data suggest agglutinability may be conditioned by more than one proteinaceous component associated with the bacterial envelope layers.