Authors
A Irvine1; S A Huws1; L Atkinson1; A Mousley1; 1 Queen's University Belfast, UK Discussion
Antimicrobial Peptides (AMPs) are ancient innate immune effectors that are found in all classes of life. In invertebrates, AMPs play key roles as the first line of defence against microbial pathogens including bacteria, viruses and fungi. Most of the currently available data on invertebrate AMPs has been derived from members of phylum Arthropoda. Phylum Nematoda comprises both free-living and parasitic worms that frequently reside in microbial-rich environments and are also likely to possess a diverse AMP repertoire. Characterisation of nematode-derived AMPs is key to unravelling the complexities of host-worm-microbiome interactions, and has the potential to reveal a novel source of antimicrobial peptide diversity that could be exploited for novel therapeutics. In this study we characterised the AMP profile across phylum Nematoda by (i) mining 134 nematode genomes for the five known nematode AMP families [Cecropins, Diapausins, Defensins, Nemapores and Glycine Rich Secreted Peptides (GRSPs)] in a homology-based BLAST/HMM approach and (ii) employing AMP-directed machine learning prediction tools to identify novel nematode AMPs.
We show that nematodes are AMP-rich, encoding > 5000 AMP genes representing the five known AMP families. Genome and transcriptome analyses reveal that: (i) AMP family profiles are influenced by nematode lifestyle in that free-living nematodes appear to have an expansion of AMPs relative to their parasitic counterparts; (ii) AMP family profiles are variable across nematode clades (Cecropins and Diapausins are highly restricted, whereas Defensins, Nemapores and GRSPs are more widely distributed); (iii) AMPs are upregulated in key nematode parasite life stages that are exposed to the host microbial environment. We have also identified 337 putative ‘high confidence’ AMPs across phylum Nematoda and preliminary data indicate broad spectrum bactericidal activity for a number of these novel AMPs against a range of key gram-negative and gram-positive bacterial pathogens.
These data indicate that phylum Nematoda has a diverse array of AMPs and underscore the need to interrogate AMP function to unravel their importance to nematode biology. 
