Dual regulation between the two-component system PhoRP and AdpA regulates antibiotic production in Streptomyces

Journal of Industrial Microbiology & Biotechnology - Antibiotic production during secondary metabolism in Streptomyces spp. is elaborately controlled by multiple environmental signals and...     

The A-factor regulatory cascade and cAMP in the regulation of physiological and morphological development in Streptomyces griseus

In the A-factor regulatory cascade leading to the onset of streptomycin biosynthesis and aerial mycelium formation in Streptomyces griseus, the A-factor receptor protein (ArpA) serves as a DNA-binding repressor and A-factor releases the repression by binding to ArpA and dissociating it from the DNA. Mutants defective in arpA therefore produce streptomycin and aerial hyphae in the absence of A-factor. A gene that inhibits streptomycin production and aerial hyphae formation in an arpA mutant was cloned on a high-copy-number plasmid and found to encode a eukaryotic-type adenylate cyclase (CyaA). Consistent with this, an exogenous supply of cAMP at high concentration almost abolished streptomycin production and aerial hyphae formation. On the other hand, cAMP at lower concentrations stimulated or accelerated these developmental processes. The effects of cAMP were detectable only in arpA mutants, and not in the wild-type strain; an exogenous supply of cAMP or cyaA disruption in the wild-type strain caused almost no effect on these phenotypes. Thus the effects of cAMP became apparent only in the arpA-defective background. cAMP at high concentrations inhibited stringent response factor ppGpp production, which is important for the onset of antibiotic biosynthesis. cAMP also influenced the timing of tyrosine phosphorylation of more than nine proteins. These findings show that a cAMP regulatory relay for physiological and morphological development functions in a concerted and interdependent way with other signal transduction pathways. Journal of Industrial Microbiology & Biotechnology (2001) 27, 177–182. Received 21 September 1999/ Accepted in revised form 14 September 2000     

Role of acid metabolism in Streptomyces coelicolor morphological differentiation and antibiotic biosynthesis

Studies of citrate synthase (CitA) were carried out to investigate its role in morphological development and biosynthesis of antibiotics in Streptomyces coelicolor. Purification of CitA, the major vegetative enzyme activity, allowed characterization of its kinetic properties. The apparent K(m) values of CitA for acetyl coenzyme A (acetyl-CoA) (32 microM) and oxaloacetate (17 microM) were similar to those of citrate synthases from other gram-positive bacteria and eukaryotes. CitA was not strongly inhibited by various allosteric feedback inhibitors (NAD(+), NADH, ATP, ADP, isocitrate, or alpha-ketoglutarate). The corresponding gene (citA) was cloned and sequenced, allowing construction of a citA mutant (BZ2). BZ2 was a glutamate auxotroph, indicating that citA encoded the major citrate synthase allowing flow of acetyl-CoA into the tricarboxylic acid (TCA) cycle. Interruption of aerobic TCA cycle-based metabolism resulted in acidification of the medium and defects in morphological differentiation and antibiotic biosynthesis. These developmental defects of the citA mutant were in part due to a glucose-dependent medium acidification that was also exhibited by some other bald mutants. Unlike other acidogenic bald strains, citA and bldJ mutants were able to produce aerial mycelia and pigments when the medium was buffered sufficiently to maintain neutrality. Extracellular complementation studies suggested that citA defines a new stage of the Streptomyces developmental cascade.     

The effect of feedback regulation and in situ product removal on the conversion of sugar to cycloheximide by Streptomyces griseus

An addition of cycloheximide to cycloheximide-producing Streptomyces griseus cultures resulted in reductions in the production rate and in the conversion of sugar into cycloheximide. In situ cycloheximide adsorption was observed to enhance: total cycloheximide titers; productivities; and the conversion of sugar to cycloheximide. During the secondary metabolite-producing phase, sugar consumption was observed to be linearly dependent on cycloheximide productivity. From this analysis a true product yield and maintenance coefficient were estimated to be 0.08 g cycloheximide/g glucose and 0.028 g glucose/g cell-h, respectively. The sixfold difference between this true product yield and a theoretical value obtained from knowledge of the biosynthetic pathway is discussed. Since the maintenance sugar requirement for cycloheximide production is large, stimulation of biosynthesis through in situ adsorption significantly increases the overall efficiency of sugar conversion to this secondary metabolite.     

Cyclic AMP regulation of tylosin biosynthesis and secondary metabolism in Streptomyces fradiae

Adenosine 3':5' cyclic monophosphate seems to regulate antibiotic biosynthesis and secondary metabolism in tylosin-producing cultures of Streptomyces fradiae C373.1. A dose-dependent response is observed by exogenous additions of dibutyryl cyclic AMP (cAMP), and is related to the nutritional status of the culture. Addition of cAMP to cultures growing in nutritionally lean media caused higher cumulative antibiotic tigers and some cellular differentiation compared with the control. In nutritionally rich media, a qualitatively different behavior resulted: an almost instantaneous shift toward secondary metabolism occurred. The response is characterized by extensive cellular differentiation with little growth and only a trace of antibiotic production. The possible role of cyclic AMP n the regulation of tylosin biosynthesis and secondary metabolism and its relation to specific nutrient limitations in synthetic, defined media in Streptomyces fradiae is discussed. (c) 1994 John Wiley & Sons, Inc.