Interspecies regulation of the recA gene of gram-negative bacteria lacking an E. coli-like SOS operator

Abstract

The recA genes of Agrobacterium tumefaciens, Rhizobium meliloti, Rhizobium phaseoli and Rhodobacter sphaeroides, species belonging to the alpha-group bacteria of the Proteobacteria class, have been fused in vitro to the lacZ gene of Escherichia coli. By using a mini-Tn5 transposon derivative, each of these recA-lacZ fusions was introduced into the chromosome of each of the four species, and into that of E. coli. The recA genes of three of the alpha bacteria are induced by DNA damage when inserted in A. tumefaciens, R. phaseoli or R. meliloti chromosomes. The expression of the recA gene of R. sphaeroides is DNA damage-mediated only when present in its own chromosome; none of the genes is induced in E. coli. Likewise, the recA gene of E. coli is not induced in any of the four alpha species. These data indicate that A. tumefaciens, R. meliloti and R. phaseoli possess a LexA-like repressor, which is able to block the expression of their recA genes, as well as that of R. sphaeroides, but not the recA gene of E. coli. The LexA repressor of R. sphaeroides does not repress the recA gene of A. tumefaciens, R. meliloti, R. phaseoli or E. coli.

The uvrB gene of Pseudomonas aeruginosa is not DNA damage inducible

“…The UV-mediated response of the lexA-lacZ fusion of P. aeruginosa (å) inserted into its own chromosome is also shown as a control. ␤-Galactosidase activities were assayed in duplicate or triplicate as described previously (16). Data presented are representative results from at least two experiments.…”

“…Afterwards, the 7.9-kb PvuII fragment from plasmid pUA578, which contained the inactivated uvrB gene, was cloned in the pSUP202 plasmid, obtaining pUA579. This plasmid was transferred to a Rif r derivative of P. aeruginosa as reported previously (16). Mercury-resistant transconjugants were screened for loss of vector-mediated tetracycline resistance to detect putative mutants that had exchanged their wild-type alleles for the inactivated uvrB allele as a consequence of a double-crossover event.…”

Characterization of the promoter of the Rhizobium etli recA gene

“…The R. etli CNPAF512 wild-type strain used in this study was previously classified as Rhizobium leguminosarum biovar phaseoli (25). Antibiotics were added to the culture media at the appropriate concentration for each bacterial species (20).…”

“…Nevertheless, others, such as those belonging to the alpha group of the class Proteobacteria-Agrobacterium tumefaciens (24), Rhizobium etli (formerly Rhizobium phaseoli) (16), Rhodobacter sphaeroides, and Rhodobacter capsulatushave no E. coli-like SOS box (2,8). However, expression of these recA genes is enhanced by DNA damage in their own genetic backgrounds but not in that of E. coli (7,20). This increase requires a RecA ϩ phenotype, indicating that a regulatory element must be present in the promoters of these recA genes.…”

“…This increase requires a RecA ϩ phenotype, indicating that a regulatory element must be present in the promoters of these recA genes. Moreover, this regulatory sequence does not appear to be the same in all members of the alpha group of the class Proteobacteria, since A. tumefaciens, R. meliloti, and R. etli recA genes are inducible when introduced into either of these three bacteria but not when introduced into the phototrophic bacteria Rhodobacter sphaeroides and Rhodobacter capsulatus (20).…”