Drosophila versus Mycobacteria: host-pathogen interactions between Drosophila melanogaster and Mycobacterium abscessus

Abstract

Host-pathogen interactions are shaped by many factors and can determine infection outcomes, often by influencing the host immune response and bacterial virulence. This project applied the genetic tractability of D. melanogaster to explore the interactions with M. abscessus in the context of the innate and cellular immune responses. M. abscessus is an emerging pathogen that represents a major threat to individuals with cystic fibrosis, with infection rates increasing globally. The genetic determinants of M. abscessus virulence are poorly understood, partly due to a lack of genetic tools. Using CRISPR-Cas9, I produced M. abscessus knockout strains targeting a variety of genes to study their role during infection and identify host factors they may interact with. This included the M. abscessus tad locus, loss of which causes increased pellicle biofilm formation, decreased intercellular adhesion and prolonged D. melanogaster survival. By manipulating host and microbial genetics, I found the increase in D. melanogaster survival during infection with tad knockout strains was due to TNFα signalling. This suggests the tad deletion mutations acquired in a dominant circulating clone of M. abscessus may promote initial colonisation and transmission at the expense of resistance against immune responses. Amino acid uptake by M. abscessus was also found to influence D. melanogaster immune responses, identified by knockout of an asparagine permease. Asparagine-limited M. abscessus resulted in longer-lived flies without significant change in bacterial loads. This survival increase can be attributed to cytokine signalling in D. melanogaster, with possible links to dysregulated insulin signalling. This demonstrates that asparagine uptake in M. abscessus prior to infection is not required for replicative fitness in vivo but does influence the interaction with the host. This work has characterised D. melanogaster as a model for M. abscessus infection, highlighting the importance of the physical properties and metabolic status of a microbe in influencing host-pathogen interactions.