The ecological impact of a bacterial weapon: microbial interactions and the Type VI secretion system

Abstract

Bacteria inhabit all known ecological niches and establish interactions with organisms from all kingdoms of life. These interactions are mediated by a wide variety of mechanisms and very often involve the secretion of diverse molecules from the bacterial cells. The Type VI secretion system (T6SS) is a bacterial protein secretion system that uses a bacteriophage-like machinery to secrete a diverse array of effectors, usually translocating them directly into neighbouring cells. These effectors display toxic activity in the recipient cell, making the T6SS an effective weapon during inter-bacterial competition and interactions with eukaryotic cells. Over the last two decades, microbiology research has experienced a shift towards using systems-based approaches to study the interactions between diverse organisms and their communities in an ecological context. Here, we focus on this aspect of the T6SS. We consider how our perspective of the T6SS has developed and examine what is currently known about the impact that bacteria deploying the T6SS can have in diverse environments, including niches associated with plants, insects and mammals. We consider how T6SS-mediated interactions can affect host organisms by shaping their microbiota, as well as the diverse interactions that can be established between different microorganisms through the deployment of this versatile secretion system.

Diversity and distribution of Type VI Secretion System gene clusters in bacterial plasmids

“…This nanomolecular apparatus has been associated with interbacterial relationships, acting as a toxin (called effectors) delivery vehicle through the cell envelope of a donor bacterium to prokaryotic and/or eukaryotic cells. Several roles have been implicated in this system, such as interbacterial killing and growth inhibition, nutrient scavenging, host colonization, kin discrimination, and acquisition of genetic material 1 – 4 .…”

Complete Genome Sequence of Achromobacter sp. Strain 77, a Hyphosphere Isolate of Fusarium oxysporum f. sp. cucumerinum

“…Seventy-nine genes putatively coding for chemotaxis proteins and type VI secretion systems might contribute to the interactions with F. oxysporum f. sp. cucumerinum hyphae and plants ( 9 – 11 ).…”

The Type VI Secretion Systems in Plant-Beneficial Bacteria Modulate Prokaryotic and Eukaryotic Interactions in the Rhizosphere

“…Many bacteria also have short-range mechanisms for the delivery of weapons or other products when in direct contact with sister cells or cells of other rhizosphere inhabitants of which the Type VI Secretion System (T6SS) is one of the best studied examples ( Basler, 2015 ; Cianfanelli et al, 2016 ; Smith et al, 2020 ). It is becoming increasingly clear that T6SS mediate interactions important for competitive fitness in a variety of environments ( Gallegos-Monterrosa and Coulthurst, 2021 ), although their roles in rhizosphere community dynamics and benefits to plant-beneficial bacteria is not well understood.…”