Bacterial Colonization of a Formulated Abalone Diet During Extended Immersion

The characteristics of the microbiota of a formulated abalone (Haliotis laevigata) diet were studied by scanning electron microscopy (SEM) and standard bacterial culture and taxonomic techniques. Microbes colonizing the diet (ABCHOW) were enumerated by SEM and partly identified after immersion of the diet in seawater for 0, 2, and 4 days with and without abalone. The fatty acid composition of the diet was also analyzed, after similar treatments, for biomass estimates and bacterial biomarker identification. Bacterial numbers on unimmersed diet and diet immersed in sterile seawater for 2 and 4 days were negligible. Bacteria proliferated after 2 days immersion in seawater with abalone (1.2 x 105 cells/mm2) and without abalone (5.7 x 104 cells/mm2) (p < .05). Numbers continued to rise between 2 and 4 days for diet immersed without abalone (6.5 x 104 cells/mm2). However, a decrease in bacterial numbers was observed between 2 and 4 days immersion in seawater with abalone (7.7 x 104 cells/mm2 after 4 days), and this was accompanied by an increase in ciliate numbers (from 0 to 102 ciliates/mm2). Ten distinct taxonomic groups of bacteria were identified from the diet after immersion; Cytophaga spp, was the most abundant group. Chemotaxonomic analysis, including fatty acid profiling, failed to provide microbial biomass estimates or bacterial biomarkers. The majority of the microbes were found to have the capacity to degrade a protein and a lipid source within the diet, but not two carbohydrate sources, including the binder. Bacteria were found to affect the physical form of the diet, but it is unlikely that they affected its macronutritional value to any great extent.