CULTURE CONDITIONS THAT INFLUENCE ACCUMULATION OF ZWITTERMICIN-A BY BACILLUS-CEREUS UW85

Bacillus cereus strain UW85 produces an antibiotic, designated zwitter micin A, that is associated with the ability of UW85 to suppress dampi ng-off disease of alfalfa (Medicago sativa) caused by the oomycete pat hogen, Phytophthora medicaginis, in a laboratory bioassay. We have ide ntified certain culture conditions that promote or suppress zwittermic in A accumulation by UW85. Maximum accumulation was detected in supern atants of trypticase soy broth cultures after sporulation, which is wh en cultures of UW85 provide the greatest suppression of damping-off on alfalfa. Inorganic amendments to trypticase soy broth cultures had th e following effects on zwittermicin A accumulation and disease suppres sion: phosphate (50 mM or more) reduced zwittermicin A accumulation an d disease suppression; ferric iron (0.25-1.0 mM) enhanced zwittermicin A accumulation and disease suppression; micronutrients (manganese, bo ron, copper, molybdenum, zinc) had no effect on zwittermicin A accumul ation or disease suppression. Cultures of UW85 grown in chemically def ined minimal medium supplemented with casein hydrolysate or grown in d efined medium containing the minimal requirements for growth supplemen ted with five amino acids (Gin, Arg, Met, Phe, Ile) accumulated zwitte rmicin A. In minimal medium, alfalfa seed exudate inhibited growth of UW85, whereas alfalfa sprout exudate enhanced zwittermicin A accumulat ion by 40%. These data indicate that the accumulation of zwittermicin A can be modulated by specific nutrients, inorganic compounds, and pla nt-derived factors. These results will facilitate the improvement of l arge-scale purification of zwittermicin A, suggest appropriate conditi ons under which to conduct further genetic and biochemical analyses, a nd further substantiate the association between antibiotic accumulatio n and disease suppression by UW85.