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•Extracellular vesicles of P. aeruginosainhibit the initial growth of S. aureus.•P. aeruginosaextracellular vesicles have no bactericidal effect against S. aureus.•P. aeruginosaextracellular vesicles reduce S. aureuspyruvate-fermenting enzymes.•Effect of P. aeruginosaextracellular vesicles is abolished by pyruvate and oxygen.

Analysis of the nucleotide sequence downstream from the Xanthomonas oryzaepv. oryzae recAgene reveals two orfs designated orfXand recX. The former has the potential to code for a 5.6 kDa protein of unknown function while the latter encodes for a putative 14.6 kDa protein with homology to RecX from various bacteria. Northern blot analysis and RT‐PCR results show that recA‐orfX‐recXare co‐regulated and arranged in an operon. A recXmutant was constructed. The mutant has no obvious growth defects or stress response defects, except that it cannot support high‐level expression of recAfrom an expression vector. Introduction of the plasmid containing recAinto the recXmutant resulted in reduced transformation efficiency and all transformants tested had mutations with reduced RecA levels. Moreover, the recXmutant has reduced basal levels of RecA. This has not been observed in other bacteria. When inactivated recXwas complemented in trans, both changes were reversed. recXmutation has no effect on the regulation of the recApromoter, suggesting that its effect on the RecA level could be post‐transcriptional.

Transcription regulation of Xanthomonas oryzaepv. oryzae recAwas characterized. Primer extension experiments showed that recAis transcribed from three promoters designated P1, P2 and P3. The sequences of −10 and −35 regions of these promoters have moderate homology to the proposed consensus sequence for a Xanthomonaspromoter. Putative SOS boxes were identified in the vicinity of P1 and P2 promoters. Deletion analysis and in vivo monitoring of promoter activity of these promoters revealed that the three promoters have different characteristics. P1 and P2 show stress‐inducible high and low promoter strengths respectively. P3 is a non‐inducible moderate promoter strength. These promoters are regulated by two SOS boxes. The multiplicity of promoters and SOS boxes provides back‐up systems to ensure proper regulation of recA.

Nucleotide sequence of Xanthomonas oryzaepv. oryzae(Xoo) DNA from pSM‐A1 was determined and sequence analysis revealed an ORF with high homology to RecA proteins. Expression analysis using an anti‐RecA antibody demonstrates that MMS treatment induces recAin Xanthomonasstrains but not in an Escherichia coliharbouring cloned Xoo recA. This indicates the existence of a recAregulatory mechanism in Xanthomonasthat is not function in E. coli. In Xoo, recAwas highly induced by treatments with chemical mutagens, UV and peroxides, while superoxides, a thiol agent, a heavy metal and heat shock were not inducers. The increased amount of RecA induced by H2O2or MMS treatments were due to increased transcription of recA. recAshowed no growth phase or starvation regulation. The pattern of recAregulation in Xoocould play important roles in stress survival in the environment and during plant‐microbe interactions.

Analysis of the nucleotide sequence downstream from the Xanthomonas oryzae pv. oryzae recA gene reveals two orfs designated orfX and recX. The former has the potential to code for a 5.6 kDa protein of unknown function while the latter encodes for a putative 14.6 kDa protein with homology to RecX from various bacteria. Northern blot analysis and RT-PCR results show that recA-orfX-recX are co-regulated and arranged in an operon. A recX mutant was constructed. The mutant has no obvious growth defects or stress response defects, except that it cannot support high-level expression of recA from an expression vector. Introduction of the plasmid containing recA into the recX mutant resulted in reduced transformation efficiency and all transformants tested had mutations with reduced RecA levels. Moreover, the recX mutant has reduced basal levels of RecA. This has not been observed in other bacteria. When inactivated recX was complemented in trans, both changes were reversed. recX mutation has no effect on the regulation of the recA promoter, suggesting that its effect on the RecA level could be post-transcriptional.

Nucleotide sequence of Xanthomonas oryzae pv. oryzae (Xoo) DNA from pSM-A1 was determined and sequence analysis revealed an ORF with high homology to RecA proteins. Expression analysis using an anti-RecA antibody demonstrates that MMS treatment induces recA in Xanthomonas strains but not in an Escherichia coli harbouring cloned Xoo recA. This indicates the existence of a recA regulatory mechanism in Xanthomonas that is not function in E. coli. In Xoo, recA was highly induced by treatments with chemical mutagens, UV and peroxides, while superoxides, a thiol agent, a heavy metal and heat shock were not inducers. The increased amount of RecA induced by H2O2 or MMS treatments were due to increased transcription of recA. recA showed no growth phase or starvation regulation. The pattern of recA regulation in Xoo could play important roles in stress survival in the environment and during plant-microbe interactions.