Identification of an Antagonistic Probiotic Combination Protecting Ornate Spiny Lobster ('Panulirus ornatus') Larvae against 'Vibrio owensii' Infection

'Vibrio owensii' DY05 is a serious pathogen causing epizootics in the larviculture of ornate spiny lobster 'Panulirus ornatus'. In the present study a multi-tiered probiotic screening strategy was used to identify a probiotic combination capable of protecting 'P. ornatus' larvae (phyllosomas) from experimental 'V. owensii' DY05 infection. From a pool of more than 500 marine bacterial isolates, 91 showed definitive in vitro antagonistic activity towards the pathogen. Antagonistic candidates were shortlisted based on phylogeny, strength of antagonistic activity, and isolate origin. Miniaturized assays used a green fluorescent protein labelled transconjugant of 'V. owensii' DY05 to assess pathogen growth and biofilm formation in the presence of shortlisted candidates. This approach enabled rapid processing and selection of candidates to be tested in a phyllosoma infection model. When used in combination, strains 'Vibrio' sp. PP05 and 'Pseudoalteromonas' sp. PP107 significantly and reproducibly protected 'P. ornatus' phyllosomas during vectored challenge with 'V. owensii' DY05, with survival not differing significantly from unchallenged controls. The present study has shown the value of multispecies probiotic treatment and demonstrated that natural microbial communities associated with wild phyllosomas and zooplankton prey support antagonistic bacteria capable of in vivo suppression of a pathogen causing epizootics in phyllosoma culture systems.