Regulation of 'Conditional' Aerial Mycelium Mutants of Streptomycetes

Abstract

Hickey–Tresner agar was originally developed to yield large amounts of aerial mycelium and spores with a variety of Streptomyces strains. Two mutant strains, S. coelicolor M110 and S. alboniger 504, behaved unusually when grown on this medium in that no aerial mycelium was formed. With the former strain, abundant formation of aerial mycelium and spores was found on other media. These variants have been defined as being aerial mycelium-conditional, because the absence or presence of wild-type morphology is dependent on the type of growth medium. This defect is due to the formation and excretion of excess acid and can be reversed by raising the pH above 7 either by growing certain aerial mycelium- negative strains of streptomycetes or Sarcina lutea near these variants, by raising the pH with a suitable buffer or, in the case of S. coelicolor M110, by adding exogenous adenine.