Role of Acinetobacter baylyi Crc in Catabolite Repression of Enzymes for Aromatic Compound Catabolism

Abstract

Here, we describe for the first time the Crc (catabolite repression control) protein from the soil bacterium Acinetobacter baylyi. Expression of A. baylyi crc varied according to the growth conditions. A strain with a disrupted crc gene showed the same growth as the wild type on a number of carbon sources. Carbon catabolite repression by acetate and succinate of protocatechuate 3,4-dioxygenase, the key enzyme of protocatechuate breakdown, was strongly reduced in the crc strain, whereas in the wild-type strain it underwent strong catabolite repression. This strong effect was not based on transcriptional regulation because the transcription pattern of the pca-qui operon (encoding protocatechuate 3,4-dioxygenase) did not reflect the derepression in the absence of Crc. pca-qui transcript abundance was slightly increased in the crc strain. Lack of Crc dramatically increased the mRNA stability of the pca-qui transcript (up to 14-fold), whereas two other transcripts (pobA and catA) remained unaffected. p-Hydroxybenzoate hydroxylase activity, encoded by pobA, was not significantly different in the absence of Crc, as protocatechuate 3,4-dioxygenase was. It is proposed that A. baylyi Crc is involved in the determination of the transcript stability of the pca-qui operon and thereby effects catabolite repression.The introduction of aromatic compounds into the central energy conservation pathways is accomplished in Acinetobacter baylyi via the ␤-ketoadipate pathway (25). In Acinetobacter, this pathway contains two parallel branches separated in terms of enzymes, as well as regulation of expression, converting the two starting compounds protocatechuate and catechol into succinyl coenzyme A and acetyl coenzyme A (21). Protocatechuate breakdown requires six catalytic steps; the respective genes (pca genes), together with genes for one of several funneling pathways (qui genes), form a large operon (the pca-qui operon, about 14 kbp) (10). Regulation of the expression of this operon is directed from the intergenic region located upstream of this large gene cluster. Several levels of transcriptional regulation of pca-qui gene expression have been described, most of which have a negative effect and therefore serve to prevent gene expression. Only one mechanism causes induction at the otherwise weak promoter upstream of pcaI (pcaIp), namely, the activity of the regulator PcaU (22). In its absence, the pca-qui genes are expressed at a fairly high basal level. PcaU decreases this basal expression level. In the presence of the inducer protocatechuate, PcaU brings about high induction and is thus both a repressor and an activator (47, 53). PcaU is an IclR family member and binds to a site between the pca-qui genes and its own gene containing three repetitions of a 10-bp DNA sequence, which are all necessary for induction (29,36). Additional regulatory levels of higher priority can prevent induction despite the continued presence of the inducer (Fig. 1). One is a mechanism that seems to organize gene expression priorities between the two ...

CrcZ and CrcX regulate carbon source utilization inPseudomonas syringaepathovartomatostrain DC3000

“…Although some members of the Pseudomonacaeae such as Acinetobacter and Morexella contain PcnB homologs, our model did not detect candidate ncRNAs in these cases. Acinetobacter baylyi does have a Crc protein involved in catabolite repression control and aromatic compound catabolism and Crc is reported to act post-transcriptionally as in the Pseudomonads, 20 but in contrast to the Pseudomonads, it displays a strong effect on transcript stability. It is possible that in Acinetobacter, the levels of Crc are modulated at the transcript level and there is no requirement for ncRNAs.…”

An ompR-envZ Two-Component System Ortholog Regulates Phase Variation, Osmotic Tolerance, Motility, and Virulence in Acinetobacter baumannii Strain AB5075

“…A. baumannii encodes a CAP homolog known as Vfr (47% identity and 73% similarity to CAP from E. coli) that also has strong homology to the same protein in P. aeruginosa and has not been shown to play a role in catabolite repression. The Crc protein has been shown to function in catabolite repression in Acinetobacter baylyi (a nonpathogenic A. baumannii relative), but Crc has not been associated with the osmotic stress response in this organism (37).…”

The β-ketoadipate pathway of Acinetobacter baylyi undergoes carbon catabolite repression, cross-regulation and vertical regulation, and is affected by Crc

“…The molecular mechanisms of CCR are well understood in Escherichia coli and Gram-positive bacteria such as Bacillus subtilis, but not in bacteria belonging to the genera Pseudomonas and Acinetobacter. In these bacteria, organic acids such as succinate and acetate, as well as the protein Crc (catabolite repression control), play an important role in CCR (Wolff et al, 1991;Zimmermann et al, 2009). A. baylyi Crc has been shown to be involved in the degradation of the pcaqui transcript, which encodes enzymes dealing with quinate and PCA degradation (Zimmermann et al, 2009).…”

“…In these bacteria, organic acids such as succinate and acetate, as well as the protein Crc (catabolite repression control), play an important role in CCR (Wolff et al, 1991;Zimmermann et al, 2009). A. baylyi Crc has been shown to be involved in the degradation of the pcaqui transcript, which encodes enzymes dealing with quinate and PCA degradation (Zimmermann et al, 2009). In Pseudomonas putida, Crc affects the expression of genes involved in aromatic compound degradation (ben, cat, pca and pobA) (Morales et al, 2004).…”