Different csrA Expression Levels in C versus K-12 E. coli Strains Affect Biofilm Formation and Impact the Regulatory Mechanism Presided by the CsrB and CsrC Small RNAs

Escherichia coli C is a strong biofilm producer in comparison to E. coli K-12 laboratory strains due to higher expression of the pgaABCD operon encoding the enzymes for the biosynthesis of the extracellular polysaccharide poly-β-1,6-N-acetylglucosamine (PNAG). The pgaABCD operon is negatively regula...

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Published in:Microorganisms (Basel) 2021-05, Vol.9 (5), p.1010
Main Authors: Carzaniga, Thomas, Falchi, Federica A., Forti, Francesca, Antoniani, Davide, Landini, Paolo, Briani, Federica
Format: Article
Language:English
Subjects:
auto-aggregation
Bacteria
Binding sites
biofilm
Biofilms
Biosynthesis
CsrA
E coli
Exonuclease
Gene expression
Hypotheses
Kinases
N-Acetylglucosamine
pgaABCD operon
Phosphorylase
Plasmids
PNPase
poly-β-1,6-N-acetylglucosamine
Polynucleotide phosphorylase
Polysaccharides
Post-transcription
Proteins
Reagents
Regulatory mechanisms (biology)
RNA polymerase
RNA-binding protein
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Summary:Escherichia coli C is a strong biofilm producer in comparison to E. coli K-12 laboratory strains due to higher expression of the pgaABCD operon encoding the enzymes for the biosynthesis of the extracellular polysaccharide poly-β-1,6-N-acetylglucosamine (PNAG). The pgaABCD operon is negatively regulated at the post-transcriptional level by two factors, namely CsrA, a conserved RNA-binding protein controlling multiple pathways, and the RNA exonuclease polynucleotide phosphorylase (PNPase). In this work, we investigated the molecular bases of different PNAG production in C-1a and MG1655 strains taken as representative of E. coli C and K-12 strains, respectively. We found that pgaABCD operon expression is significantly lower in MG1655 than in C-1a; consistently, CsrA protein levels were much higher in MG1655. In contrast, we show that the negative effect exerted by PNPase on pgaABCD expression is much stronger in C-1a than in MG1655. The amount of CsrA and of the small RNAs CsrB, CsrC, and McaS sRNAs regulating CsrA activity is dramatically different in the two strains, whereas PNPase level is similar. Finally, the compensatory regulation acting between CsrB and CsrC in MG1655 does not occur in E. coli C. Our results suggest that PNPase preserves CsrA-dependent regulation by indirectly modulating csrA expression.
ISSN:2076-2607
2076-2607
DOI:10.3390/microorganisms9051010