High-Frequency Conjugation System Facilitates Biofilm Formation and pAMβ1 Transmission by Lactococcus lactis

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Abstract
The importance of conjugation as a mechanism to spread biofilm determinants among microbial populations was illustrated with the gram-positive bacterium Lactococcus lactis. Conjugation triggered the enhanced expression of the clumping protein CluA, which is a main biofilm attribute in lactococci. Clumping transconjugants further transmitted the biofilm-forming elements among the lactococcal population at a much higher frequency than the parental nonclumping donor. This cell-clumping-associated high-frequency conjugation system also appeared to serve as an internal enhancer facilitating the dissemination of the broad-host-range drug resistance gene-encoding plasmid pAMβ1 within L. lactis, at frequencies more than 10,000 times higher than those for the nonclumping parental donor strain. The implications of this finding for antibiotic resistance gene dissemination are discussed.