Effect of biopolymers on geldanamycin production and biocontrol ability of Streptomyces melanosporofaciens strain EF-76

The biocontrol agent Streptomyces melanosporofaciens strain EF-76 produces geldanamycin, an ansamycin antibiotic which displays antagonistic activity towards several Gram-positive bacteria and fungi. Biopolymers [chitin, carboxymethylcellulose (CMC) and xylan] or N-acetylglucosamine were added to S. melanosporofaciens culture media and the effect of these additional carbon sources on geldanamycin production was analysed. Geldanamycin biosynthesis was only stimulated in the presence of 1 g L-1 of chitin. Higher concentrations of chitin, as well as the presence of CMC or xylan, did not improve antibiotic production. N-acetylglucosamine, the final degradation product of chitin, did not stimulate geldanamycin production at all concentrations tested. Nevertheless, the addition of chitin in culture media had no or a negative impact on the antagonistic activity of EF-76 towards the pathogen Streptomyces scabies. Furthermore, the effect of chitin, CMC and xylan on the biocontrol ability of EF-76 against S. scabies was tested on radish seedlings. None of the polymers affected the biocontrol efficiency of EF-76 under gnotobiotic conditions. However, the addition of CMC or xylan to plant growth medium protected radish seedlings against S. scabies infection.