pBL1 impairs cellobiose metabolism in Lactococcus lactis

pBL1 is a Lactococcus lactis theta-replicating 10.9-kbp plasmid that encodes the synthetic machinery of the bacteriocin Lcn972. In this work, the transcriptomes of exponentially growing L. lactis with and without pBL1 were compared. A discrete response was observed with a total of ten genes showing significantly changed expression. Up-regulation of the lactococcal oligopeptide uptake system (opp) was observed, likely linked to a higher nitrogen demand required for Lcn972 biosynthesis. Striking, celB coding for the membrane porter IIC of the cellobiose-PTS and the upstream gene llmg0186 were down-regulated. Growth profiles for L. lactis strains MG1363, MG1363/pBL1 and MG1363ΔcelB grown in CDM-cellobiose confirmed slower growth of pBL1 and ΔcelB while no differences were scored on glucose. The presence of pBL1 shifted the fermentation products towards a mixed acid profile and promoted substantial changes in intracellular pool sizes for glycolytic intermediates in cellobiose-growing cells as determined by HPLC and NMR. Overall, these data support the genetic evidence of a constriction in cellobiose uptake. Notably, several cell wall precursors accumulated, while other UDP-activated sugars pools were lower, which could reflect rerouting of precursors towards the production of structural or storage polysaccharides. Moreover, slow cellobiose-growing cells and those lacking celB were more tolerant to Lcn972 than cellobiose adapted cells. Thus, down-regulation of celB could help to build-up a response against the antimicrobial activity of Lcn972 enhancing self-immunity of the producer cells. The transcriptomes of Lactococcus lactis MG1614 with and without the bacteriocinogenic plasmid pBL1, grown under laboratory conditions, were compared using three biological replicates.