The RNA processing enzyme polynucleotide phosphorylase negatively controls biofilm formation by repressing poly-N-acetylglucosamine (PNAG) production in Escherichia coli C

Thomas Carzaniga,Davide Antoniani,Gianni Dehò,Paolo Landini,Federica Briani

doi:10.1186/1471-2180-12-270

Thomas Carzaniga, Davide Antoniani + Show 3 more

Open Access

https://doi.org/10.1186/1471-2180-12-270

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Journal: BMC microbiology	Publication Date: Nov 21, 2012
Citations: 93	License type: cc-by

Affiliation: University of Milan

Abstract

BackgroundTransition from planktonic cells to biofilm is mediated by production of adhesion factors, such as extracellular polysaccharides (EPS), and modulated by complex regulatory networks that, in addition to controlling production of adhesion factors, redirect bacterial cell metabolism to the biofilm mode.ResultsDeletion of the pnp gene, encoding polynucleotide phosphorylase, an RNA processing enzyme and a component of the RNA degradosome, results in increased biofilm formation in Escherichia coli. This effect is particularly pronounced in the E. coli strain C-1a, in which deletion of the pnp gene leads to strong cell aggregation in liquid medium. Cell aggregation is dependent on the EPS poly-N-acetylglucosamine (PNAG), thus suggesting negative regulation of the PNAG biosynthetic operon pgaABCD by PNPase. Indeed, pgaABCD transcript levels are higher in the pnp mutant. Negative control of pgaABCD expression by PNPase takes place at mRNA stability level and involves the 5’-untranslated region of the pgaABCD transcript, which serves as a cis-element regulating pgaABCD transcript stability and translatability.ConclusionsOur results demonstrate that PNPase is necessary to maintain bacterial cells in the planktonic mode through down-regulation of pgaABCD expression and PNAG production.

Highlights

Transition from planktonic cells to biofilm is mediated by production of adhesion factors, such as extracellular polysaccharides (EPS), and modulated by complex regulatory networks that, in addition to controlling production of adhesion factors, redirect bacterial cell metabolism to the biofilm mode
Ectopic expression of RNase II suppressed the aggregative phenotype of the pnp mutant (Figure 1B, right panel), suggesting that such a phenotype is controlled by the RNA degrading activity of Polynucleotide phosphorylase (PNPase)
We investigated the mechanism of pgaABCD regulation by PNPase and its possible connections with known regulatory networks controlling pgaABCD expression. pgaABCD expression is positively regulated at the transcription initiation level by NhaR, while pgaABCD mRNA stability and translation are negatively regulated by the CsrA protein [51,52]

Summary

Introduction

Transition from planktonic cells to biofilm is mediated by production of adhesion factors, such as extracellular polysaccharides (EPS), and modulated by complex regulatory networks that, in addition to controlling production of adhesion factors, redirect bacterial cell metabolism to the biofilm mode. Extensive production of extracellular polysaccharides (EPS) represents a defining feature of bacterial biofilms; EPS are the major constituent of the so-called “biofilm matrix”, which includes cell surface-associated proteins and nucleic acids [4,5]. Expression of genes involved in EPS biosynthesis is controlled by complex regulatory networks responding to a variety of environmental and physiological cues, including stress signals, nutrient availability, temperature, etc. The vps genes, involved in EPS biosynthesis in Vibrio cholerae, are regulated at the transcription level by the CytR protein, in response to intracellular pyrimidine concentrations [14].

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