The production of specialized metabolites by
Streptomyces
bacteria is usually temporally regulated. This regulation is complex and frequently involves both global and pathway-specific mechanisms.
Streptomyces ambofaciens
ATCC23877 produces several specialized metabolites, including spiramycins, stambomycins, kinamycins and congocidine. The production of the first three molecules has been shown to be controlled by one or several cluster-situated transcriptional regulators. However, nothing is known regarding the regulation of congocidine biosynthesis. Congocidine (netropsin) belongs to the family of pyrrolamide metabolites, which also includes distamycin and anthelvencins. Most pyrrolamides bind into the minor groove of DNA, specifically in A/T-rich regions, which gives them numerous biological activities, such as antimicrobial and antitumoral activities. We previously reported the characterization of the pyrrolamide biosynthetic gene clusters of congocidine (
cgc
) in
S. ambofaciens
ATCC23877, distamycin (
dst
) in
Streptomyces netropsis
DSM40846 and anthelvencins (
ant
) in
Streptomyces venezuelae
ATCC14583. The three gene clusters contain a gene encoding a putative transcriptional regulator,
cgc1
,
dst1
and
ant1
respectively. Cgc1, Dst1 and Ant1 present a high percentage of amino acid sequence similarity. We demonstrate here that Cgc1, an atypical orphan response regulator, activates the transcription of all
cgc
genes in the stationary phase of
S. ambofaciens
growth. We also show that the
cgc
cluster is constituted of eight main transcriptional units. Finally, we show that congocidine induces the expression of the transcriptional regulator Cgc1 and of the operon containing the resistance genes (
cgc20
and
cgc21
, coding for an ABC transporter), and propose a model for the transcriptional regulation of the
cgc
gene cluster.
Importance
Understanding the mechanisms of regulation of specialized metabolite production can have important implications both at the level of specialized metabolism study (expression of silent gene clusters) and the biotechnological level (increase of the production of a metabolite of interest). We report here a study on the regulation of the biosynthesis of a metabolite from the pyrrolamide family, congocidine. We show that congocidine biosynthesis and resistance is controlled by Cgc1, a cluster-situated regulator. As the gene clusters directing the biosynthesis of the pyrrolamides distamycin and anthelvencin encode a homolog of Cgc1, our findings may be relevant for the biosynthesis of other pyrrolamides. In addition, our results reveal a new type of feed-forward induction mechanism, in which congocidine induces its own biosynthesis through the induction of the transcription of
cgc1
.