Type 3 Fimbriae and Biofilm Formation Are Regulated by the Transcriptional Regulators MrkHI in Klebsiella pneumoniae

Department of Microbiology, Roy J and Lucille A Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.
Journal of bacteriology (Impact Factor: 2.69). 05/2011; 193(14):3453-60. DOI: 10.1128/JB.00286-11
Source: PubMed

ABSTRACT Klebsiella pneumoniae is an opportunistic pathogen which frequently causes hospital-acquired urinary and respiratory tract infections. K. pneumoniae may establish these infections in vivo following adherence, using the type 3 fimbriae, to indwelling devices coated with extracellular matrix components. Using a colony immunoblot screen, we identified transposon insertion mutants which were deficient for type 3 fimbrial surface production. One of these mutants possessed a transposon insertion within a gene, designated mrkI, encoding a putative transcriptional regulator. A site-directed mutant of this gene was constructed and shown to be deficient for fimbrial surface expression under aerobic conditions. MrkI mutants have a significantly decreased ability to form biofilms on both abiotic and extracellular matrix-coated surfaces. This gene was found to be cotranscribed with a gene predicted to encode a PilZ domain-containing protein, designated MrkH. This protein was found to bind cyclic-di-GMP (c-di-GMP) and regulate type 3 fimbrial expression.

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Available from: Jeremiah Johnson, Aug 14, 2014
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    • "The pLN126_33 cassette also encodes a highly truncated gene from the downstream region of mrkF. In K. pneumoniae this region contains the mrkHIJ control cassette [38], [39], where mrkJ encodes an EAL-domain phosphodiesterase shown to regulate expression of mrkABCDF through cleavage of the signalling molecule cyclic-di-GMP [40]. The existence of three different lengths of mobile mrkABCDF cassettes suggests a general course of evolution for adaptive loads that result from the recruitment of chromosomal gene cassettes. "
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    PLoS ONE 08/2012; 7(7):e41259. DOI:10.1371/journal.pone.0041259 · 3.23 Impact Factor
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    • "Although the formation of biofilms by K. pneumoniae is still not fully understood, several key determinants have been identified such as pili, polysaccharides, quorum sensing and transport and regulatory proteins [7-13]. More recently, it has been shown that c-di-GMP controls type 3 fimbria expression and biofilm formation in K. pneumoniae by binding to and modulating the activity of the transcriptional regulator MrkH [14,15]. The second messenger c-di-GMP is known to play a key role in several cellular functions as well as in biofilm formation in bacteria where it modulates the transition between planktonic and sessile lifestyles. "
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    BMC Microbiology 07/2012; 12(1):139. DOI:10.1186/1471-2180-12-139 · 2.98 Impact Factor
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    • "It could be speculated that several putative regulatory genes present in or up- and down-stream from the type 1 and type 3 fimbriae gene clusters might be part of a complex regulatory network. Thus, the fimK gene, which is unique to the K. pneumoniae fim gene cluster, has been shown to up-regulate type 1 fimbrial expression when deleted, and the mrkH gene has been shown to regulate type 3 fimbrial expression (Rosen et al., 2008; Johnson et al., 2011; Wilksch et al., 2011). Interestingly, both of these regulatory genes encode proteins that have internal domains capable of interaction with cycling di-GMP, a global bacterial second messenger believed to be involved in virulence regulation of many gram-negative bacterial species (Jonas et al., 2009; Struve et al., 2008; Bobrov et al., 2005; Johnson et al., 2011). "
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    ABSTRACT: Urinary catheters are standard medical devices utilized in both hospital and nursing home settings, but are associated with a high frequency of catheter-associated urinary tract infections (CAUTI). In particular, biofilm formation on the catheter surface by uropathogens such as Klebsiella pneumoniae causes severe problems. Here we demonstrate that type 1 and type 3 fimbriae expressed by K. pneumoniae enhance biofilm formation on urinary catheters in a catheterized bladder model that mirrors the physico-chemical conditions present in catheterized patients. Furthermore, we show that both fimbrial types are able to functionally compensate for each other during biofilm formation on urinary catheters. In situ monitoring of fimbrial expression revealed that neither of the two fimbrial types is expressed when cells are grown planktonically. Interestingly, during biofilm formation on catheters, both fimbrial types are expressed, suggesting that they are both important in promoting biofilm formation on catheters. Additionally, transformed into and expressed by a nonfimbriated Escherichia coli strain, both fimbrial types significantly increased biofilm formation on catheters compared with the wild-type E. coli strain. The widespread occurrence of the two fimbrial types in different species of pathogenic bacteria stresses the need for further assessment of their role during urinary tract infections.
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