Probiont niche specialization contributes to additive protection against 'Vibrio owensii' in spiny lobster larvae

The development of efficient probiotic application protocols for use in marine larviculture relies on comprehensive understanding of pathogen-probiont-host interactions. The probiont combination of 'Pseudoalteromonas' sp. PP107 and 'Vibrio' sp. PP05 provides additive protection against vectored 'Vibrio owensii' DY05 infection in larvae (phyllosomas) of ornate spiny lobster, 'Panulirus ornatus'. Here, fluorescently tagged strains were used to demonstrate niche specialization of these probionts in both the live feed vector organism 'Artemia' and in phyllosomas. The pathogen was vulnerable to direct interaction with PP05 in the bacterioplankton as well as in the 'Artemia' gut and the phyllosoma foregut and midgut gland. In contrast, PP107 was localized on external surfaces of 'Artemia' and phyllosomas, and direct interaction with the pathogen was limited to the bacterioplankton. While PP107 was the overall dominant ectobiont on the phyllosoma cephalothorax and inner leg segments, PP05 was the primary colonizer of outer leg segments, nutrient-rich locales that may promote ingestion during feeding. This study shows that niche specialization can contribute to the additive probiotic effect of a probiotic mixture and highlights that probiotic enrichment of 'Artemia' cultures can intercept the infection cycle of 'V. owensii' DY05 in early-stage 'P. ornatus' phyllosomas.