Conjugation between two Escherichia coli strains and between Escherichia coli (donor) and Azospirillum brasilense (recipient) in the presence of various herbicides

The effects of various herbicides on conjugation (transfer of RP4 plasmid) between two strains of Escherichia coli and between E. coli (donor) and Azospirillum brasilense (recipient) were studied. Prior to the conjugation experiment, the growth of these bacteria in the presence of herbicides was examined. It was observed that except methyl viologen none of these herbicides exert any inhibitory effect on growth. In the presence of methyl viologen the growth of both E. coli strains was completely and the growth of A. brasilense partially inhibited. The conjugation ability of these strains was studied in liquid media and in soil. In liquid media it was observed that except ethiozin all tested herbicides did not affect the conjugation between the E. coli strains. In the presence of ethiozin the formation of transconjugants was partially inhibited. Ethiozin also affected the transfer of the RP4 plasmid between E. coli and A. brasilense. On the other hand, in liquid media atrazine and isoproturon promoted the conjugation of these two strains. In soil the herbicides metamitron, metribuzin and ethiozin, belonging to the as‐triazine group, stimulated the conjugation between two E. coli strains. The results obtained during this work indicate that the pesticides exert an influence on the conjugation and this process is a useful and simple tool to evaluate the influence of xenobiotics on the genetic transfer between microorganisms.

Key words:

• Herbicides
• Escherichia coli
• Azospirillum brasilense