The Putative Lactococcal Extracytoplasmic Function Anti-Sigma Factor Llmg2447 Determines Resistance to the Cell Wall-Active Bacteriocin Lcn972

Abstract

bLactococcin 972 (Lcn972) is a cell wall-active bacteriocin that inhibits cell wall biosynthesis in Lactococcus lactis. In this work, the transcriptomes of the Lcn972-resistant (Lcn r ) mutant L. lactis D1 and its parent strain were compared to identify factors involved in Lcn972 resistance. Upregulated genes included members of the cell envelope stress (CesSR) regulon, the penicillinbinding protein pbpX gene and gene llmg2447, which may encode a putative extracytoplasmic function (ECF) anti-sigma factor. The gene llmg2447 is located downstream of the nonfunctional ECF gene sigX pseudo . Nisin-controlled expression of llmg2447 led to high Lcn972 resistance in L. lactis, with no cross-resistance to other cell wall-active antimicrobials. Upregulation of llmg2447 in L. lactis D1 (Lcn r ) was linked to the integration of insertion element IS981 into the llmg2447 promoter region, replacing the native ؊35 box and activating the otherwise silent promoter P 2447 . This is the first example of an orphan ECF anti-sigma factor involved in bacteriocin resistance. This new role in neutralizing cell wall-active compounds (e.g., Lcn972) could have evolved from a putative primary function of Llmg2447 in sensing cell envelope stress.

Disruption of a Transcriptional Repressor by an Insertion Sequence Element Integration Leads to Activation of a Novel Silent Cellobiose Transporter in Lactococcus lactis MG1363

“…L. lactis MG1363 possesses 71 copies in a total of 11 different types of IS elements, of which IS981 (27) and IS905 (28) are the most abundant (14 copies and 16 copies, respectively) (4). IS981 has been described to be involved in adaptation of L. lactis MG1363 and IL1403 to unfavorable conditions during starvation or oxidative-or bacteriocin-induced stress (9,10,29). A recombination event between two IS905 elements has been shown to be responsible for a large chromosomal inversion in L. lactis NCDO763, although no resulting phenotypic changes could be observed in comparison to MG1363.…”

Antimicrobial Peptides Produced by Bacteria: The Bacteriocins

“…This is the case, for example, of a putative regulator of an extracytoplasmic function sigma factor, which protected lactococcal cells against the cell wall-active bacteriocin Lcn972 (Roces et al 2012a).…”

Resistance to bacteriocins produced by Gram-positive bacteria

“…lactis. llmg2447 is predicted to encode a putative anti-sigma factor (Roces et al, 2012b). An elevated expression of this gene led to high lactococcin 972 resistance (a 400-fold decrease in susceptibility) in La.…”

“…An elevated expression of this gene led to high lactococcin 972 resistance (a 400-fold decrease in susceptibility) in La. lactis, with no cross-resistance to nisin, bacitracin, penicillin G and vancomycin (Roces et al, 2012b). However, the way in which Llmg2447 protects La.…”

“…However, the way in which Llmg2447 protects La. lactis from lactococcin 972 remains to be elucidated (Roces et al, 2012b).…”