A New Front in Microbial Warfare-Delivery of Antifungal Effectors by the Bacterial Type VI Secretion System

Bacteria and fungi are ubiquitous in nature and co-colonise numerous environmental niches. Focussing on the human host, such cross-kingdom interactions are prevalent within the human microbiota, and are commonly associated with biofilms and medically relevant infections. The type VI secretion system (T6SS) is widely used by bacteria to fire diverse effector proteins directly into neighbouring target cells. Many bacterial pathogens employ T6SSs as a potent weapon to deliver antibacterial effector proteins into rival bacterial cells during inter-bacterial competition. However. recently the exciting discovery was made that this 'anti-bacterial' T6SS is also a potent anti-fungal weapon, eliciting anti-fungal effectors that are able to kill pathogenic fungal species. Our pilot data indicate that T6SS-dependent anti-fungal activity is widespread, and mediated by a variety of different anti-fungal effectors, similar to anti-bacterial T6SSs. As bacterial and fungal species co-exist in the human microbiome and disease-causing infections, we predict that anti-fungal T6SSs will shape many diverse microbial communities relevant to human health. The goal of this current project is to take key steps in establishing this exciting new research field by investigating the medical importance and molecular basis of T6SS mediated anti-fungal activity.

Defining the molecular basis of T6SS mediated anti-fungal activity will be undertaken in Prof Jan Quinn's laboratory. Specific techniques include RNA-Seq of T6SS-intoxicated fungal cells to define the genome-wide fungal transcriptional responses elicited by specific effectors, and SGA genetic screens will generate the genetic interaction network for each effector. Such non-biased approaches will direct subsequent molecular and biochemical experiments to define the precise mechanism employed by effectors to kill the fungal cell target.
To explore the physiological relevance of T6SS mediated anti-fungal activity, a unique ex vivo human intestinal enteroid ("mini guts") model established in Dr Chris Stewarts's laboratory will be employed to explore how anti-fungal T6SSs can influence the nature and outcome of bacterial-fungal co-colonisation of the human gut. This is important as alterations in the intestinal microbiome are associated with human health and many diseases (3), and roles for the T6SS in the success of both commensal and pathogenic bacteria within gut communities have been recently described.