Fig. 1. Heterogenous expression of a predicted effector protein LqqE1 of the Lysobacter enzymogenes type IVA secretion system in Pseudomonas fluorescens impaired the AHL production.

A Schematic illustration of thirteen predicted type IVA secretion system effector (T4E) proteins encoded by L. enzymogenes OH11. B A procedure showing the steps of screening the L. enzymogenes T4E genes with capacities to block the AHL production in P. fluorescens 2P24 after expression by plasmid. The lqqE1 expression significantly blocked the AHL production in P. fluorescens 2P24 that is indicated by the AHL production zone (C) and beta-galactosidase activity (D) determined by an AHL biosensor JZA1. E The lqqE1 expression in P. fluorescens 2P24 did not affect the bacterial growth. F Pseudomonas fluorescens 2P24 expressing lqqE1 showed a significant decrease on biofilm formation that is a known AHL-controlled function. 2P24, wild type of P. fluorescens, served as a positive control; gfp, a negative control; momL encoding a known AHL-degrading enzyme was used as an additional positive control; ΔpcoI, a mutant of P. fluorescens 2P24 lacking the AHL synthase (PcoI) gene and served as an additional negative control. AHL production was calculated by measuring the area of the blue circle around the colony. Average data from three experiments was presented, ±SD. ***p < 0.0001, “ns” stands for not statistically significant, assessed by one-way ANOVA.