IDENTIFICATION OF EXOPOLYSACCHARIDES PRODUCED BY FLUORESCENT PSEUDOMONADS ASSOCIATED WITH COMMERCIAL MUSHROOM (AGARICUS-BISPORUS) PRODUCTION

The acidic exopolysaccharides (EPSs) from 63 strains of mushroom produ ction-associated fluorescent pseudomonads which were mucoid on Pseudom onas agar F medium (PAF) were isolated, partially purified, and charac terized. The strains were originally isolated from discolored lesions which developed postharvest on mushroom (Agaricus bisporus) caps or fr om commercial lots of mushroom casing medium. An acidic galactoglucan, previously named marginalan, was produced by mucoid strains of the sa prophyte Pseudomonas putida and the majority of mucoid strains of sapr ophytic P. fluorescens (biovars III and V) isolated from casing medium . One biovar II strain (J1) of P. fluorescens produced alginate, a cop olymer of mannuronic and guluronic acids, and one strain (H13) produce d an apparently unique EPS containing neutral and amino sugars. Of 10 strains of the pathogen ''P. gingeri,'' the causal agent of mushroom g inger blotch, 8 gave mucoid growth on PAF. The ''P. gingeri'' EPS also was unique in containing both neutral sugar and glucuronic acid. Muco id, weakly virulent strains of ''P. reactans'' produced either alginat e or marginalan. All 10 strains of the pathogen P. tolaasii, the causa l agent of brown blotch of mushrooms, were nonmucoid on PAF. Productio n of EPS by these 10 strains plus the 2 nonmucoid strains of ''P. ging eri'' also was negative on several additional solid media as well as i n two broth media tested. The results support our previous studies ind icating that fluorescent pseudomonads are a rich source of novel EPSs.