PLEIOTROPIC EFFECTS OF CAMP ON GERMINATION, ANTIBIOTIC BIOSYNTHESIS AND MORPHOLOGICAL DEVELOPMENT IN STREPTOMYCES-COELICOLOR

In wild-type Streptomyces coelicolor MT1110 cultures, cyclic adenosine 3',5' monophosphate (cAMP) was synthesized throughout the development al programme with peaks of accumulation both during germination and la ter when aerial mycelium and actinorhodin were being produced. Constru ction and characterization of an adenylate cyclase disruption mutant ( BZ1) demonstrated that cAMP facilitated these developmental processes. Although pulse-labelling experiments showed that a similar germinatio n process was initiated in BZ1 and MT1110, germ-tube emergence was sev erely delayed in BZ1 and never occurred in more than 85% of the spores . Studies of growth and development on solid glucose minimal medium (S MMS, buffered or unbuffered) showed that MT1110 and BZ1 produced acid during the first rapid growth phase, which generated substrate myceliu m. Thereafter, on unbuffered SMMS, only MT1110 resumed growth and prod uced aerial mycelium by switching to an alternative metabolism that ne utralized its medium, probably by reincorporating and metabolizing ext racellular acids, BZ1 was not able to neutralize its medium or produce aerial mycelium on unbuffered SMMS; these defects were suppressed by high concentrations (>1 mM) of cAMP during early growth or on buffered medium, Other developmental mutants (bldA, bldB, bldC, bldD, bldG) al so irreversibly acidified this medium. However, these bald mutants wer e not suppressed by exogenous cAMP or neutralizing buffer. BZ1 also di fferentiated when it was cultured in close proximity to MT1110, a prop erty observed in cross-feeding experiments between bald mutants and co mmonly thought to reflect diffusion of a discrete positively acting si gnalling molecule, In this case, MT1110 generated a more neutral pH en vironment that allowed BZ1 to reinitiate growth and form aerial myceli um, The fact that actinorhodin synthesis could be induced by concentra tions of cAMP (< 20 mu M) found in the medium of MT1110 cultures, sugg ested that it may serve as a diffusible signalling molecule to co-ordi nate antibiotic biosynthesis.