T6SS-mediated competitive exclusion amongPantoea agglomeransassociated with plants

Abstract

Establishment of symbiotic interactions with a host habitat depends on colonization success of the microbiome members. One route to success is increasing competitiveness against genotypes having similar adaptations. Many bacteria deploy the type VI secretion system (T6SS) to deliver toxic effector proteins into the cytoplasm of competing cells, whereas the attacking cells are protected from self-intoxication by immunity proteins. While the evolution of antagonistic interactions between species competing for similar niches is expected, the interactions between closely related strains having a similar core genetic makeup, remains understudied. Here we show that the strength of T6SS-mediated competition between closely related P. agglomerans strains is not associated with phylogenetic relatedness and rather depends on their effector and immunity genes repertoire. Annotating the T6SS components in eleven P. agglomerans isolates from wheat seeds, we observed a heterogeneous composition of effector and immunity determinants. Competition experiments further showed profound differences in the strain survival following reciprocal T6SS-mediated interactions. Reconstructing the evolution of T6SS loci across plant-associated P. agglomerans isolates indicates intra-chromosomal recombination as the main driver of effector and immunity gene diversification. Our results provide empirical data on intraspecific interactions during microbiota assembly likely to be at play during colonization of germinating plant seeds.

The role of the type VI secretion system in the stress resistance of plant-associated bacteria

“… 2023 ; Zhang et al 2023 ). Most plant-associated bacteria that possess the T6SS have strong viability when they coexist with other bacteria (Bernal et al 2018 ; Ripcke et al 2023 ). The study of plant-associated bacterial T6SS shows that this competitive advantage is achieved by injecting toxic effector proteins into rival bacteria via the T6SS to kill or inhibit their growth (Whitney et al 2013 ; Tang et al 2018 ).…”