Journal of Bacteriology, May 2001, p. 3184-3192, Vol. 183, No. 10
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.10.3184-3192.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


Department of Molecular Microbiology, Biozentrum, University of Basel, Basel,1 and Institute of Biotechnology, ETH-Zürich, HPT, Zürich,2 Switzerland
Received 6 September 2000/Accepted 8 February 2001
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 Km
values of CitA for acetyl coenzyme A (acetyl-CoA) (32 µM) and
oxaloacetate (17 µM) 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
-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.
Present address: Department of Developmental Biology, Stanford
University School of Medicine, Stanford, CA 94305-5329.
Present address: Morphochem, Basel, BS 4058, Switzerland.
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