Journal of Microbiology

Research Support, Non-U.S. Gov't

NtrC-Sensed Nitrogen Availability Is Important for Oxidative Stress Defense in Pseudomonas putida KT2440: Sujin Yeom , Jinki Yeom , Woojun Park; J. Microbiol. 2010;48(2):153-159. Published online May 1, 2010; DOI: https://doi.org/10.1007/s12275-010-0075-0

Abstract: The zwf, which encodes glucose-6-phosphate dehydrogenase, is repressed by NtrC under nitrogen-limited condition. Previously, we demonstrated that induction of zwf-1 is required for protecting Pseudomonas putida cells under oxidative stress, which could be possible probably because of derepression of HexR on the zwf-1 gene under oxidative stress. These findings led us investigate that NtrC still represses the zwf-1 under nitrogen-limited oxidative stress condition, which makes cells more sensitive under such condition. Interestingly, deletion of the ntrC gene significantly reduces growth rate, but renders cells more resistant to oxidative stress, under nitrogen limited condition in P. putida. More vitality of the ntrC mutant under oxidative stress condition was also confirmed by the fluorogenic redox dye using flow cytometry. The results of transcriptome analysis demonstrated that the derepression of several oxidative stress genes along with the zwf-1 gene might confer high resistance to oxidative stress in the ntrC mutant. Here, we presented the data for the first time, showing that different sets of genes are involved in nitrogen-rich and nitrogen-limited oxidative stress conditions and NtrC-sensed nitrogen availability is one of the most important prerequisite for full cellular defense against oxidative stress in P. putida.

Regulation of fpr Gene encoding NADPH :Ferredoxin oxidoreductase by the soxRS locus in escherichia coli: Koh, Young Sang , Chouh, Jenny , Roe, Jung Hye; J. Microbiol. 1996;34(2):137-143.

Abstract: We isolated a promoter inducible by paraquat, a superoxide-generating agent, from Escherichia coli using a promoter-probing plasmid pRS415. From sequence analysis we found out the promoter is for fpr ENCODING nadph : ferredoxin oxidoreductase. We constructed on operon fusion of lacZ gene with fpr promoter to monitor the expression of the gene in the single-copy state. LacZ expression generators, menadione and plumbagin, also induced the expression of β-galactosidase in the fusion strain. On the other hand, no significant induction was observed by treatment with hydrogen peroxide, ethanol, and heat shock. Induction of β-galactosidase was significantly reduced by introducing a Δsox 8 :: cat of soxS3 :: Tn10 mutation into the fusion strain, indicating that fpr gene is a member of the soxRS regulon. The transcriptional start site was determined by primer extension analysis. Possible roles of fpr induction in superoxide stress were discussed.

Isolation and Characterization of Paraquat-inducible Promoters from Escherichia coli: Lee, Joon Hee , Roe, Jung Hye; J. Microbiol. 1997;35(4):277-283.

Abstract: Promoters inducible by paraquat, a superocide-generating agent, were isolated from Escherichia coli using a promoter-probing plasmid pRS415 with promoterless lacA gene. Twenty one promoters induced by paraquat were selected and further characterized. From sequence analysis, thirteen of the promoters were mapped to their specific loci on the Escherichia coli chromosome. Several promoters were mapped to the upstream of known genes such as usgl, katG, and mglB, whose relationships with superoxide response have not been previously reported. Other promoters were mapped to the upstream region of unknown open reading frames. Downstream of HC 96 promoter are uncharacterized ORFs whose sequences are homologous to ABC-transporter subunits. Downstream of HC84 promoter is an ORF encoding a transcriptional regulator-like protein, which contains a LysR family-specific HTH (helix-turn-helix) DNA bindign motif. We investigated whether these promoters belong to the soxRS regulon. All promoters except HC96 were found to belong to the soxRS regulon. The HC96 promoter was significantly induced by paraquat in the soxRS deletion mutant strain. The basal transcription level of three promoters (HE43, HC71, HD94) significantly increased at the stationary phase, implying that they are regulated by RpoS. However, paraquat inducibility of all promoters disappeared in the stationary phase, suggesting that SoxRS regulatory system is active only in rapidly growing cells.

Regulation of the sufABCDSE Operon by Fur: Joon-Hee Lee , Won-Sik Yeo , Jung-Hye Roe; J. Microbiol. 2003;41(2):109-114.

Abstract: A promoter that is inducible by paraquat and menadione, the superoxide generators, independently of soxRS has been found in front of the sufABCDSE operon in Escherichia coli. Based on the observation that SufA is a holomog of IscA that functions in the assembly of iron sulfur cluster and the sufA promoter (sufAp) contains a putative Fur-binding consensus, we investigated whether this gene is regulated by Fur, a ferric uptake regulator. When examined in several sufAp-lacZ chromosomal fusion strains, sufAp was induced by EDTA, an iron chelator and a well-known Fur-inducer. The basal level of sufA expression increased dramatically in fur mutant, suggesting repression of sufAp by Fur. The derepression in fur mutant and EDTA-induction of sufA expression required nucleotides up to -61, where a putative Fur box is located. Purified Fur protein bound to the DNA fragment containing the putative Fur box between -35 and -10 promoter elements. The regulation by Fur and menadione induction of sufAp acted independently. The rpoS mutation increased sufA induction by menadione, suggesting that the stationary sigma factor RpoS acts negatively on sufA induction.

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