An engineered bacteriocin paracin wx7-1 for chili pepper preservation: Controlling soft rot and its dual-target...

Soft rot caused by Pectobacterium carotovorum subsp. carotovorum (Pcc) leads to severe postharvest losses in chili pepper, highlighting an urgent need for novel preservation techniques. Due to the Gram-negative nature of Pcc, common bacteriocins like nisin are ineffective. Here, we engineered a novel bacteriocin, paracin wx7-1, which exhibited enhanced activity against the pathogen Pcc with a minimum inhibitory concentration (MIC) of 16 μM, 8-fold lower than that of its template. Paracin wx7-1 exerted concentration-dependent bactericidal effects, achieving >99.9% lethality at ≥8MIC. In vivo, 8MIC paracin wx7-1 treatment reduced disease incidence from 65% to 15% on the first day and 100% to 68.33% on the fourth day, compared to the control. Additionally, a 24-hour pre-incubation of paracin wx7-1 elicited a better resistance response in pepper. SEM revealed reduced bacterial colonization on pepper surface and damage to the Pcc cell membrane. Physiological assays confirmed that paracin wx7-1 disrupted membrane integrity, depolarized membrane potential, increased inner/outer membrane permeability of Pcc. RNA-seq and RT-qPCR analysis of Pcc revealed that paracin wx7-1 exerted its antibacterial effect by coordinately downregulating genes essential for core metabolic processes (carbohydrate and amino acid metabolism) and structural integrity (ribosome, cell wall/membrane), thereby compromising bacterial viability and pathogenicity. RNA-seq and RT-qPCR analysis of green pepper revealed that paracin wx7-1 induced systemic resistance by reprogramming defense-related metabolism, MAPK signaling, and plant-pathogen interaction components. This study presents a promising bacteriocin with dual action, direct pathogen inhibition and host resistance induction, for controlling pepper soft rot.