Lactococcus lactis is widely used as a dairy starter and is becoming a recognized cell factory. In both applications, cells are exposed to stressful conditions that compromise the integrity of the cell envelope, a cellular structure crucial for survival. To understand how L. lactis responds to damage to its cell envelope, we have pursued an evolutionary experimental approach to evolve laboratory and industrial strains able to cope with Lcn972, a bacteriocin that inhibits cell wall synthesis during cell division. Lactococcal cultures were successively exposed to increasing concentrations of Lcn972 (adaptation) followed by growing in the absence of the stressor (stabilization) to fix mutations in the population. Through genome sequencing and transcriptional studies, it was found that resistance to Lcn972 is accomplished by induction of llmg2447, specifying a putative anti-ECF sigma factor in the laboratory strain MG1614. In industrial strains and field isolates, mutations accumulated mostly in genes specifying for a Bce-like module involved in sensing and resistance to antimicrobial peptides. In several Lcn972R clones, this Bce-like module, which has been proven to confer resistance to Lcn972, is constitutively activated. Nevertheless, variant analyses and genome-wide transcriptomics pointed to additional mechanisms and plausible metabolic adaptations whose protecting role against Lcn972 remains to be assessed. Longread based genome sequencing also informed us of the loss of plasmids bearing important technological traits such as resistance to bacteriophages. All-in-all, a wealth of information has been gathered that will help us to understand the grounds of the cell envelope stress response in L. lactis

Resumen del trabajo presentado en el 14th International Symposium on Lactic Acid Bacteria, celebrado en Egmond aan Zee (Países Bajos), del 27 al 31 de agosto de 2023