Impact and induction of prophages in Lactococcus lactis

Abstract

Lactic acid bacteria (LAB) are very important microorganisms in food industry, since they are used for the production of dairy products such as cheese or yogurt. Among LAB, Lactococcus lactis (gram-positive bacteria) is the main component of the starter cultures in cheese production. The technology used to manufacturing dairy products at large scale is standardized, simple and highly efficient, however, an unwanted lysis of L. lactis may have a negative impact in the final product, even causing the loss of the product. Phages are one of the causes of the lysis when they infect the cells. Temperate phages also known as prophages, can “switch” from the lysogenic state to the lytic cycle under specific environmental stress. Such induction has been widely studied and is mediated by the SOS response, although recently the cell envelope stress response (CESR) has been suggested to participate in prophage induction as well. The aim of this study was to assess the impact of two specific prophages, TP712 and CAP in growth and autolytic capacity. Additionally to elucidate the role of CESR in prophage induction, the L. lactis laboratory strains UKLc10 TP712, UKLc10 TP712/CAP and UKLc10 CAP were treated with MitC and two cell-wall antimicrobials, Lcn 972 and bacitracin, using qPCR as a quantification method to detect viral DNA. The results suggest that there is indeed, an impact of prophage content since strain UKLc10 CAP shows an adaptive advantage with a higher growth rate over the two other strains. Moreover, the lysogen carrying the two prophages is more autolytic. Interestingly, only the strain UKLc10 TP712/CAP lyses after treatment with MitC and prophage induction was observed by qPCR. In contrast, when both UKLc10 TP712 and UKLc10 TP712/CAP are treated with Lcn 972 or bacitracin, inhibition of spontaneous induction happens. The fact that we were not able to construct a ΔcesSR mutant, implies that we cannot evaluate at which extent CESR is involved in prophage induction. Further research is needed in order to find out the role of CAP and TP712 in the lysis of cells and how they behave in their coexistence as well as how CESR interferes in their lysis-lysogeny decision.