Development of a bioprocess technology for the production of Vibrio midae, a probiotic for use in abalone aquaculture

Abstract

The abalone industry of South Africa is under severe pressure due to illegal harvesting and poaching of this seafood delicacy. These abalones are harvested excessively; as a result, these animals do not have a chance to replace themselves in their habitats, ensuing in a drastic decrease in natural stocks of abalone. Abalone, has an extremely slow growth rate, and takes approximately four years to reach a size that is market acceptable, therefore, it was imperative to investigate methods to boost the overall growth rate and immunity of the animal. The University of Cape Town (UCT) began research, which resulted in the isolation of two microorganisms, a yeast isolate Debaryomyces hansenii and a bacterial isolate Vibrio midae, from the gut of the abalone and characterised them for their probiotic abilities. This work resulted in an internationally competitive concept technology that was patented. The next stage of research was to develop a suitable bioprocess to enable commercial production. Numerous steps were taken to develop an efficient production process for V. midae, one of the isolates found by UCT. The initial stages of research resulted in the development of a stable and validated cell bank which allowed the development of a robust inoculum stage. This was followed by optimization of temperature and pH which resulted in improved probiotic production at a temperature of 30oC and a pH of 6.5. Once these critical growth parameters were established further media optimization studies were performed. The two key nutrient supplements investigated were corn steep liquor (CSL) and High Test Molasses (HTM) due to their suitability, availability and affordability. The optimization of CSL (6.4 g.l-1) and HTM (24 g.l-1) concentrations in the growth medium resulted in a 180% increase in cell concentration,

a 5716-fold increase in cell productivity and a 97.2% decrease in the material cost of production when compared to the base case technology. Furthermore, a stable market ready liquid probiotic product, containing viable but not culturable (VBNC) state of Vibrio midae cells, was developed during the downstream processing aspect of the study. Finally, the validation of this production technology at full manufacturing scale was demonstrated which further enhances the attractiveness and commercial feasibility of this probiotic production process.