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Journal of Bacteriology, November 2000, p. 6137-6144, Vol. 182, No. 21
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Regulation of the rulAB Mutagenic DNA Repair Operon of Pseudomonas syringae by UV-B (290 to 320 Nanometers) Radiation and Analysis of rulAB-Mediated Mutability In Vitro and In Planta

Jae J. Kim and George W. Sundin*

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843-2132

Received 2 May 2000/Accepted 17 August 2000

The effects of the rulAB operon of Pseudomonas syringae on mutagenic DNA repair and the transcriptional regulation of rulAB following irradiation with UV-B wavelengths were determined. For a rulB::Km insertional mutant constructed in P. syringae pv. syringae B86-17, sensitivity to UV-B irradiation increased and UV mutability decreased by 12- to 14-fold. rulAB-induced UV mutability was also tracked in phyllosphere populations of B86-17 for up to 5 days following plant inoculation. UV mutability to rifampin resistance (Rifr) was detected at all sampling points at levels which were significantly greater than in nonirradiated controls. In P. aeruginosa PAO1, the cloned rulAB determinant on pJJK17 conferred a 30-fold increase in survival and a 200-fold increase in mutability following a UV-B dose of 1,900 J m-2. In comparative studies using defined genetic constructs, we determined that rulAB restored mutability to the Escherichia coli umuDC deletion mutant RW120 at a level between those of its homologs mucAB and umuDC. Analyses using a rulAB::inaZ transcriptional fusion in Pseudomonas fluorescens Pf5 showed that rulAB was rapidly induced after UV-B irradiation, with expression levels peaking at 4 h. At the highest UV-B dose administered, transcriptional activity of the rulAB promoter was elevated as much as 261-fold compared to that of a nonirradiated control. The importance of rulAB for survival of P. syringae in its phyllosphere habitat, coupled with its wide distribution among a broad range of P. syringae genotypes, suggests that this determinant would be appropriate for continued investigations into the ecological ramifications of mutagenic DNA repair.

* Corresponding author. Mailing address: Department of Plant Pathology and Microbiology, Texas A&M University, 2132 TAMU, College Station, TX 77843-2132. Phone: (979) 862-7518. Fax: (979) 845-6483. E-mail: gsundin{at}acs.tamu.edu.

Journal of Bacteriology, November 2000, p. 6137-6144, Vol. 182, No. 21
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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