Identification of a regulator that controls stationary-phase expression of catalase-peroxidase in Caulobacter crescentus.
Expression of the catalase-peroxidase of Caulobacter crescentus, a gram-negative member of the alpha subdivision of the Proteobacteria, is 50-fold higher in stationary-phase cultures than in exponential cultures. To identify regulators of the starvation response, Tn5 insertion mutants were isolated with reduced expression of a katG::lacZ fusion on glucose starvation. One insertion interrupted an open reading frame encoding a protein with significant amino acid sequence identity to TipA, a helix-turn-helix transcriptional activator in the response of Streptomyces lividans to the peptide antibiotic thiostrepton, and lesser sequence similarity to other helix-turn-helix regulators in the MerR family. The C. crescentus orthologue of tipA was named skgA (stationary-phase regulation of katG). Stationary-phase expression of katG was reduced by 70% in the skgA::Tn5 mutant, and stationary-phase resistance to hydrogen peroxide decreased by a factor of 10. Like the wild type, the skgA mutant exhibited starvation-induced cross-resistance to heat and acid shock, entered into the helical morphology that occurs after 9 to 12 days in stationary phase, and during exponential growth induced katG in response to hydrogen peroxide challenge. Expression of skgA increased 5- to 10-fold in late exponential phase. skgA is the first regulator of a starvation-induced stress response identified in C. crescentus. SkgA is not a global regulator of the stationary-phase stress response; its action encompasses the oxidative stress-hydrogen peroxide response but not acid or heat responses. Moreover, SkgA is not an alternative sigma factor, like RpoS, which controls multiple aspects of starvation-induced cross-resistance to stress in enteric bacteria. These observations raise the possibility that regulation of stationary-phase gene expression in this member of the alpha subdivision of the Proteobacteria is different from that in Escherichia coli and other members of the gamma subdivision.
Rava
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Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Somma
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Steinman
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D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D016935:Caulobacter crescentus / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005809:Genes, Regulator; D017930:Genes, Reporter; D005947:Glucose / Q000172:deficiency; D016254:Mutagenesis, Insertional; D010544:Peroxidases / Q000096:biosynthesis*; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000235:genetics*
D001426:Bacterial Proteins; C121794:SkgA protein, Caulobacter crescentus; D015534:Trans-Activators; C089891:tipA protein, Streptomyces; D010544:Peroxidases; C076136:catalase HPI; D005947:Glucose