The Lcn 972 - bacteriocin plasmid pBL 1 impairs cellobiose metabolism in 1

27 pBL1 is a Lactococcus lactis theta-replicating 10.9-kbp plasmid that encodes the 28 synthetic machinery of the bacteriocin Lcn972. In this work, the transcriptomes of 29 exponentially growing L. lactis with and without pBL1 were compared. A discrete 30 response was observed with a total of ten genes showing significantly changed 31 expression. Up-regulation of the lactococcal oligopeptide uptake system (opp) was 32 observed, likely linked to a higher nitrogen demand required for Lcn972 biosynthesis. 33 Strikingly, celB coding for the membrane porter IIC of the cellobiose-PTS and the 34 upstream gene llmg0186 were down-regulated. Growth profiles for L. lactis strains 35 MG1363, MG1363/pBL1 and MG1363ΔcelB grown in CDM-cellobiose confirmed 36 slower growth of pBL1 and ΔcelB while no differences were scored on glucose. The 37 presence of pBL1 shifted the fermentation products towards a mixed acid profile and 38 promoted substantial changes in intracellular pool sizes for glycolytic intermediates in 39 cellobiose-growing cells as determined by HPLC and NMR. Overall, these data support 40 the genetic evidence of a constriction in cellobiose uptake. Notably, several cell wall 41 precursors accumulated, while other UDP-activated sugars pools were lower, which 42 could reflect rerouting of precursors towards the production of structural or storage 43 polysaccharides. Moreover, slow cellobiose-growing cells and those lacking celB were 44 more tolerant to Lcn972 than cellobiose adapted cells. Thus, down-regulation of celB 45 could help to build-up a response against the antimicrobial activity of Lcn972 46 enhancing self-immunity of the producer cells. 47 48 49