The Effect Of RsbU On Biofilm Formation In Listeria Monocytogenes

Listeria monocytogenes,an important Gram-positive foodborne pathogen,can form biofilm in the inert or living surface,leading to an enhanced resistance against harsh conditions and a big challenge to be eliminated from food processing facilities.SigB,which is the main stress response factor of Gram-positive bacteria,plays a crucial role in the formation of biofilm,but the detailed molecular mechanism is unclear.RsbU,a signal(energy and physical chemical signals)transducer protein of the sigB operon in L monocytogenes,but whether RsbU has a similiar effect in L monocytogenes has not been reported yet.Moreover SigB partly regulated some virulence gene expression,such as inlA and inlB.Transcription of the major virulence regulator PrfA had been also reported to be related to SigB regulation.But the effect of RsbU in virulence in L monocytogenes has not been studied.To study the function of RsbU and the relationship between RsbU and SigB in biofilm formation in L monocytogenes,the single and(or)double deletion mutants of rsbU and sigB genes were constructed to compare the biofilm formation abilities with the wild-type strain under different temperature(25℃ and 37℃)and nutrition(nutrient-rich BHI medium and nutrient-poor MEM medium).The data show that deletion of RsbU or SigB significantly decreased biofilm formation ability of L monocytogenes under different temperatures and media.Moreove,low temperature(25 ℃)and poor nutritional(MEM medium)conditions facilitated RsbU transducing stress signal to active SigB,which consequently act on biofilm formation in L monocytogenes.To investigate the relationship between RsbU and the main virulence genes as well as the genes which are involving in stress response(such as cell wall synthesis or the heat shock response)and biofilm formation in L monocytogenes,we compared the transcription levels of these genes using RT-PCR between thewild strain and the RsbU deletion strains.The data show that hly,lmo1083,hrcA and sigB are significantly down-regulated while plcA and prfA are significantly up-regulated in the RsbU deletion strains,which demonstrate the significant role of RsbU invirulence and stress response in L monocytogenes.