Hha, YbaJ, and OmpA regulate Escherichia coli K12 biofilm formation and conjugation plasmids abolish motility

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Abstract
Escherichia coli Hha is an environmental‐response regulator of the pathogenic hemolysin operon, and Hha and the contiguous YbaJ are both induced 30‐fold in E. coli biofilms (Appl. Microbiol. Biotechnol. 64:515, 2004). Here it is shown that Hha and YbaJ regulate biofilm formation since the hha/ybaJ deletion reduces biofilm mass in microtitre plates (81% in minimal medium, 50% in complex medium) and in flow cells (1,000‐fold less surface coverage in minimal medium). The addition of the derepressed conjugative plasmid R1drd19, which increases significantly biofilm formation, eliminated motility completely in wild‐type E. coli K12, promoted cell aggregation 27.18 ± 0.05‐fold, and produced a flatter biofilm. Deletion of hha/ybaJ or ybaJ restored motility (this motility phenotype may be complemented by providing hha+/ybaJ+ or ybaJ+ in trans) and reduced cell aggregation to that of the wild‐type strain that lacks the conjugation plasmid. This increase in motility due to deleting hha/ybaJ was found to be due to 8‐fold induction of fliA transcription. In addition, deletion of ompA reduced biofilm mass by 80% in both LB medium and LB medium with glucose. Also, Hha/YbaJ promotes conjugation since there was five‐fold less conjugation in the hha/ybaJ mutant. It appears that conjugation plasmids promote biofilm formation by promoting cell aggregation, and that Hha and YbaJ increase biofilm formation by increasing conjugation and by decreasing motility when a conjugative plasmid (R1drd19) is present (YbaJ plays the most important role in this regulation of motility). When hha/ybaJ are deleted, there is less conjugation, less aggregation, more motility, and less biofilm.