Figure 1.

Ectopic expression of LMRG_02920 inhibits the production of virions and monocins

(A–C) Growth analysis of WT L. monocytogenes (Lm) (A) and mutants harboring deletions of the φ10403S-prophage (Δφ) (B) or of the structurallysis module of the monocin element (LMRG_02368-0278, ΔStruc-lys) (C) with or without ectopic expression of LMRG_02920 from pPL2-plasmid (pPL2-2920). Bacteria were grown in brain heart infusion (BHI) medium in the presence (+) or absence (-) of MC at 30°C. The error bars represent the standard deviation of three independent experiments and are sometimes hidden by the symbols.

(D) A plaque-forming assay (PFU) of WT Lm, WT Lm overexpressing LMRG_02920 (pPL2-2920), and a mutant deleted of the φ10403S integrase gene (LMRG_01511, Δintegrase) as a control. Virions obtained from MC-treated bacterial cultures (6 h after MC treatment) were tested on the indicator Lm strain Mack861 for plaque formation (numerated PFUs). The error bars represent the standard deviation of three independent experiments.

(E) A monocin killing assay performed with monocins obtained from MC-treated bacterial cultures (6 h after MC treatment) of WT Lm, Lm over-expressing LMRG_02920 (pPL2-2920) and a mutant lacking the mon element (Δmon), as a control. A diluted overnight culture of the indicator Lm strain ScottA was supplemented with serial dilutions of filtered supernatants containing monocins and grown at 30°C. Optical density (OD)₆₀₀ was measured after 10 h. The error bars represent the standard deviation of three independent experiments.