Highlights d H2-T6SS mediates molybdate acquisition by secretion of ModA d Expression of H2-T6SS is activated by the master regulator Anr and anaerobiosis d ModA interacts with the outer membrane protein IcmP and uses it to deliver molybdate d The T6SS-ModA-IcmP system plays a role for P. aeruginosa

The multidrug-resistant strains of food spoilage bacteria and foodborne pathogenic bacteria in food are badly in need of being controlled by effective bio-preservatives. In this study, the XN8 strain was isolated from Jiangshui and identified as Lactobacillus coryniformis according to 16S rRNA gene sequence. One of the bacteriocins produced by XN8 was purified by ammonium sulfate precipitation and a series of chromatographic column, and designated as lactocin XN8-A (LXA). The molecular mass of LXA was 3100.0242 Da by MALDI-TOF MS. The LXA showed good heat, pH and storage stabilities. However, it was sensitive to proteases. The LXA was found to have a broad antimicrobial spectrum on both Gram-positive and Gram-negative bacteria including multidrug-resistant strains and Listeria monocytogenes. Its minimum inhibitory concentration (MIC) for both E. coli and S. aureus was 6.85 μg/mL. The LXA had a bactericidal mode without cell lysis by the growth curve and time-kill assay. The results of electron microscope showed that the LXA destroyed membrane permeability and induced pore-formation of target cells. Furthermore, the LXA induced cell cycle arrest at both G1 and G2/M phase by cell cycle analysis. This research suggests that the LXA has promising potential as bio-preservative in food industry.

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The human pathogen Pseudomonas aeruginosa harbors three paralogous zinc proteases annotated as AmpD, AmpDh2, and AmpDh3, which turn over the cell wall and cell wall‐derived muropeptides. AmpD is cytoplasmic and plays a role in the recycling of cell wall muropeptides, with a link to antibiotic resistance. AmpDh2 is a periplasmic soluble enzyme with the former anchored to the inner leaflet of the outer membrane. We document, herein, that the type VI secretion system locus II (H2‐T6SS) of P. aeruginosa delivers AmpDh3 (but not AmpD or AmpDh2) to the periplasm of a prey bacterium upon contact. AmpDh3 hydrolyzes the cell wall peptidoglycan of the prey bacterium, which leads to its killing, thereby providing a growth advantage for P. aeruginosa in bacterial competition. We also document that the periplasmic protein PA0808, heretofore of unknown function, affords self‐protection from lysis by AmpDh3. Cognates of the AmpDh3‐PA0808 pair are widely distributed across Gram‐negative bacteria. Taken together, these findings underscore the importance of their function as an evolutionary advantage and that of the H2‐T6SS as the means for the manifestation of the effect.