Five homologous small RNAs are involved in the response of Listeria monocytogenes to cell wall
acting antibiotics
Nielsen PK1 and Kallipolitis BH1
1
Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej
55, DK- 5230 Odense M, Denmark
Small RNAs (sRNAs) are important regulatory elements involved in a variety of cellular responses,
including stress tolerance and virulence. In Listeria monocytogenes five homologous sRNAs,
named LhrC1-5, were identified recently by co-immunoprecipitation with the RNA chaperone
protein Hfq. The objective of the present study is to improve our understanding of the role(s) of
LhrC1-5 in L. monocytogenes. Our study involves the identification of factors that influence the
expression of LhrC1-5 and investigations of genes affected by LhrC1-5.
A range of different environmental conditions and regulatory mutant strains were employed to
identify factors that affect the expression of LhrC1-5. The presence and stability of the RNA
transcripts were determined by Northern blotting. Furthermore, expression of lhrC1-5 was followed
by construction of promoter-lacZ fusions for all five sRNA-encoding genes. These studies revealed
a differentiated transcription of LhrC1-5 in response to the presence of cell wall acting
antimicrobial agents, such as ethanol and β-lactam antibiotics. Cell wall acting agents have
previously been shown to activate the two-component systems LisRK and CesRK in L.
monocytogenes. Our experiments revealed that transcription of lhrC1-5 is completely dependent on
the presence of a functional LisRK system, whereas the CesRK system appears to be important for
a differentiated transcription of lhrC1-5 in response to the above-mentioned cell wall acting agents.
Finally, a mutant strain lacking lhrC1-5 was constructed and characterized, and genes regulated by
LhrC1-5 were investigated by comparing the global gene expression of a wild type strain vs. a
ΔlhrC1-5 mutant strain. In summary, this study shows that Listeria monocytogenes responds to cell
wall acting agents through a complex gene regulatory network which includes five small noncoding RNAs.