Tinopal AN as a selective agent for the differentiation of phytopathogenic and saprophytic Pseudomonas species

The selective toxicity of the respiratory inhibitor Tinopal AN (1,l-bis (3,N-5dimethylbenzoxazol-2-yl) methine p-toluene sulphonate) towards phytopathogenic bacteria was investigated further and in general was confirmed using more than 160 additional strains of Pseudomonas spp. The mechanism(s) of the resistance shown by saprophytic fluorescent pseudomonads were studied to elucidate the differences between resistant saprophytic and sensitive phytopathogenic Pseudomonas species. Damage to, or partial removal of the cell wall of Tinopal AN-resistant Pseudomonas aeruginosa, resulted in a marked Tinopal AN-sensitivity, as judged by the ability of Tinopal AN to inhibit oxygen uptake. Furthermore, removal of part of the lipopolysaccharide (LPS) component of the outer membrane also resulted in sensitivity. Mutants of Ps. aeruginosa with modified outer cell walls were tested for their reactions towards Tinopal AN, and two cell wall lipopolysaccharide (LPS) mutants of Escherichia coli (enu Al) and Salmonella typhimurium (rfh) were, in contrast to the wild-type strains, found to be sensitive towards Tinopal AN. The results therefore suggest that the resistance of saprophytic pseudomonads towards Tinopal AN is due (at least in part) to the selectively permeable properties of the outer membrane of the cell wall. The usefulness of Tinopal AN for screening potentially phytopathogenic strains of Pseudomonas was confirmed.