Drug resistance among parasitic nematodes has resulted in an urgent need for the development of new therapies. However, the high re-discovery rate of antinematode compounds from terrestrial environments necessitates a new repository for future drug research. Marine epiphytic bacteria are hypothesised to produce nematicidal compounds as a defence against bacterivorous predators, thus representing a promising, yet underexplored source for antinematode drug discovery. The marine epiphytic bacterium Pseudoalteromonas tunicata is known to produce a number of bioactive compounds. Screening genomic libraries of P. tunicata against the nematode Caenorhabditis elegans identified a clone (HG8) showing fast-killing activity. However, the molecular, chemical and biological properties of HG8 remain undetermined. A novel Nematode killing protein-1 (Nkp-1) encoded by an uncharacterised gene of HG8 annotated as hp1 was successfully discovered through this project. The Nkp-1 toxicity appears to be nematode-specific, with the protein being highly toxic to nematode larvae but having no impact on nematode eggs. A putative carbohydrate binding module was identified at the N-terminus of Nkp-1 protein sequence which is suggested to bind to a yet unknown nematode glycoconjugate receptor. This study also provides the first insights into the mode of action of Nkp-1 and the nematode response towards its toxicity. The Nkp-1 expressing clones; HG8 and HP1 (expressing respectively either the original 13.8 kb genomic insert of HG8 or the hp1 gene only) colonised C. elegans intestine, in addition exposure to both strains and protein extracts resulted in multiple physical damages and necrosis. As a defence, C. elegans utilised its innate and associative learned avoidance behaviour to prevent contact with the Nkp-1 strains. Further I found evidence for the involvement of daf-2/daf-16 ILR and sek-1 p38_MAPK immune pathways in response to Nkp-1 exposure and the subsequent expression of genes involved in lysozyme, superoxide dismutase production and dar (deformed anal region) formation. Moreover, this study revealed the impact of different gut microbiota has on nematode survival and the resulting physical damages upon exposure to the Nkp-1. The outcome of these studies not only kickstart the development of Nkp-1 as a future antinematode drug but has re-affirmed the potential of marine epiphytic bacteria as a new source of novel antinematode drugs.