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Type 1 fimbriae of Escherichia coil facilitate attachment to the host mucosa and promote biofilm formation on abiotic surfaces. The transcriptional regulator LrhA, which is known as a repressor of flagellar, motility and chemotaxis genes, regulates biofilm formation and expression of type 1 fimbriae. Whole-genome expression profiling revealed that inactivation of lrhA results in an increased expression of structural components of type 1 fimbriae. In vitro, LrhA bound to the promoter regions of the two fim recombinases (FimB and FimE) that catalyse the inversion of the fimA promoter, and to the invertible element itself. Translational lacZ fusions with these genes and quantification of timE transcript levels by real-time PCR showed that LrhA influences type 1 fimbrial phase variation, primarily via activation of FimE, which is required for the ON-to-OFF transition of the fim switch. Enhanced type 1 fimbrial expression as a result of lrhA disruption was confirmed by mannose-sensitive agglutination of yeast cells. Biofilm formation was stimulated by lrhA inactivation and completely suppressed upon LrhA overproduction. The effects of LrhA on biofilm formation were exerted via the changed levels of surface molecules, most probably both flagella and type 1 fimbriae. Together, the data show a role for LrhA as a repressor of type 1 fimbrial expression, and thus as a regulator of the initial stages of biofilm development and, presumably, bacterial adherence to epithelial host cells also.

Results demonstrate that GacA protein upregulates the expression of regulatory RNA, RsmZ, in Pseudomonas fluorescens CHA0 in response to a bacterial signal. This leads RsmZ to alleviate the respression activity of RsmA on target mRNAs expression.

Results demonstrate that biosynthetic autoinduction of 2,4-diacetylphloroglucinol is inhibited by certain bacterial and fungal metabolites. Data indicate that this control mechanism may balance homeostatically the amount of extracellular metabolites produced in Pseudomonas fluorescens.

A study was conducted to characterize the hcnABC gene cluster encoding hydrogen cyanide synthase and anaerobic regulation in Pseudomonas fluorescens CHA0. Triparental matings were carried out P. fluorescence recipients with Escherichia coli supporting a mobilized plasmid while the CTAB method was used to carry out small-scale preparations of plasmid DNA from E. coli. Results indicated that the anaerobic regulator ANR was needed for cyanide synthesis in the aerobic strain CHAO.

The amplification of housekeeping sigma factor gene rpoD in Pseudomonas fluorescens CHA0 appears to increase production of antibiotics and enhance protection of cucumber against Pythium ultimum. Sequencing of the P. fluorescens rpoD gene allowed its amplification using an IncP vector. Inactivation of the gene showed that is essential for survival. The CHA0 strain with the gene amplification produced several times the amount of the antibiotics pyoluteorin and 2,4-diacetylphloroglucinol than is produced in normal CHA0.

This article examines the conventional molecular biological tool, the lacZ fusions, geneticists use to study regulation of gene expression. Authors provide some cautionary notes to be aware of in such investigations, that reliable gene fusion data are obtained only when transcription start site is precisely determined.