The Lpp lipoprotein suppresses motility in a biofilm-forming strain of Escherichia coli O157:H7

Authors: Uhlich, Gaylen; Bayles, Darrell

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/28/2007
Publication Date: 7/8/2007
Citation: Uhlich, G.A., Bayles, D.O. 2007. The Lpp lipoprotein suppresses motility in a biofilm-forming strain of Escherichia coli O157:H7. International Association of Food Protection. Abstract. P5-15.

Interpretive Summary:

Technical Abstract: In Escherichia coli O157:H7 strain ATCC 43895, a guanine to thymine transversion in a gene involved in fimbrial (curlifiber) synthesis created strain 43895OR. Strain 43895OR produces an abundant extracellular matrix rich in curli fibers and generates dense biofilms on solid surfaces. We investigated the components of the extracellular matrix of strain 43895OR and their role in E. coli persistence in food environments. The soluble proteins from strains 43895OR and 43895 grown on Congo red indicator (CRI) plates were compared by one-dimensional PAGE. Two unique proteins from strain 43895OR were identified by immunoblotting and mass spectrometry. Mutants of strain 43895OR with disruption of each identified gene were created and tested for phenotypic and functional differences on CRI agar and on motility plates (0.3% agar). Transcriptional expression of the identified genes in strains 43895 and 43895OR was determined by quantitative real-time reverse-transcriptase PCR. A CsgA polyclonal antibody identified a 15-kDa protein as the curli subunit. A <10-kDa protein was identified from MALDI-TOF combined MS+MS/MS spectra as a Lpp homologue. Comparison of strains 43895 and 43895OR with lpp, csgA, or lpp/csgA mutants revealed differences in aggregation on CRI plates and in broth. In motility assays, the lpp mutant and the csgA/lpp double mutant each showed significantly (P<0.05) greater swimming motility than strains 43895OR, 43895, or the csgA mutant. However, there were no motility differences between the lpp and the csgA/lpp mutant strains. Although csgA RNA transcripts were up-regulated in strain 43895OR, lpp expression was indistinguishable between strains 43895 and 43895OR. These results indicate that curli fibers and Lpp are highly expressed during 43895OR colony growth on agar and that Lpp has a suppressive affect on swimming motility which could affect survival in a food environment. Moreover, the increased expression of Lpp is not controlled at the transcriptional level.