A Novel SRNA S015 Improves Acid Tolerance Of Lactococcus Lactis F44

Lactococcus lactis,as is widely applied in industry,productes a har mLess polycyclic antibacterial peptide nisin.Meanwhile,Lactococcus lactis may face with multitudinous kinds of stesses in the fermentation process,especially the contradiction between the accumulated acid and the depressed pH value in the fermentation process.Nisin is stable at low pH.Improving the acid tolerance of L.lactis could thus enhance nisin yield.Among multi anti-stess mechines,small non-coding RNAs(sRNA)play essential roles in acid tolerance by regulating their target mRNAs at the posttranscriptional level.sRNAs are induced by the global regulator and transcribe to interact with mRNAs.Based on RNA-sequencing analysis and qRT-PCR analysis,our lab found a series of candidant sRNAs.In this study,a novel sRNA,s015,was identified in L.lactis F44 via the use of northern blotting.s015 could improve the acid tolerance of L.lactis and boosted nisin yield at low pH.In silico predictions enabled us to construct a library of possible s015 target mRNAs.Alignment of s015 homologous sequence and sRNA-mRNA binding sites suggested that s015 contains a highly-conserved region(5'-GAAAAAAAC-3')that likely encompasses the regulatory core of the sRNA.Target genes atpG,busAB,cysD,ilvB,yudD and ywdA were verified as repessive targets of s015 while tcsR,ung are active ones.The mutation of the core regulation region elucidated the interactions between s015 and its target genes.Further study on the overexpression strains who carried target genes tested that atpG?busAB?ung and ilvB are direct genes associated with acid tolerance while ywdA may be co-regulated by s015 and another regulator.