Phenotypic variation of Pseudomonas putida and P. tolaasii affects the chemotactic response to Agaricus bisporus mycelial exudate.

The chemotactic response of wild-type Pseudomonas putida and P. tolaasii, and a phenotypic variant of each species, to Agaricus bisporus mycelial exudate was examined. Both P. putida, the bacterium responsible for initiating basidiome development of A. bisporus, and P. tolaasii, the causal organism of bacterial blotch disease of the mushroom, displayed a positive chemotactic response to Casamino acids and to A. bisporus mycelial exudate. The response was both dose- and time-dependent and marked differences were observed between the response time of the wild-type strains and their phenotypic variants. Phenotypic variants responded rapidly to both attractants and reached a maximum response after 10-20 min, whereas the wild-types took 45-60 min. The differences are partly explained by the more rapid swimming speed of the phenotypic variants. Both variants responded maximally to similar concentrations of Casamino acids and mycelial exudates. Investigations into the nature of the attractants contained in the mycelial exudate indicated that they are predominantly small (Mr less than 2000) thermostable compounds. Sugars present in the exudate did not elicit a chemotactic response in any isolate, but a mixture of 14 amino acids detected in the exudate accounted for between 50 and 75% of the chemotactic response of the fungal exudate.