Browsing by Author "Lalloo, Rajesh"
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- ItemDevelopment of a bioprocess for the production of an aquaculture biological agent(Stellenbosch : University of Stellenbosch, 2010-12) Lalloo, Rajesh; Gorgens, Johann F.; University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: Biological agents offer several opportunities to address the many challenges faced in intensive reticulated aquaculture. We therefore isolated and selected Bacillus spp. as potential biological agents, because this group has demonstrated an array of biological activities of possible benefit to aquaculture. They also display advantages in terms of robustness during bioprocessing and end product application. Natural isolates obtained from Cyprinus carpio, selected as a model high-value ornamental fish species, and associated culture environments, were purified and assessed for in vitro efficacy based on the inhibition of growth of pathogenic Aeromonas hydrophila and the decrease in concentrations of ammonium, nitrite, nitrate and phosphate ions, typically found as waste products in aquaculture systems. Based on suitability for aquaculture application, isolates B001, B002 and B003 were selected and further evaluated in vitro and in an in vivo trial with C. carpio. Inhibition of Aer. hydrophila growth and a decrease in concentrations of waste ions were demonstrated in these studies. Based on 16S RNA sequence homology, the isolates were identified as Bacillus subtilis, B. cereus and B. licheniformis, respectively. High sequence homology between B. subtilis and B. anthracis necessitated further safety studies on the best isolate, B. cereus NRRL100132 (B002). The isolate was shown not to contain the anthrax virulence genes pOX1, pOX2 or the B. cereus enterotoxin. Elucidation of the potential modes of action of a biological agent facilitates an understanding of functionality and encourages technology uptake by end users. Competitive exclusion through growth rate and competitive uptake of glucose and iron, the latter facilitated by siderophore production, were shown to be key mechanisms at play in inhibition of Aer. hydrophila by the B. cereus isolate. As production cost is an important consideration in development of commercially relevant biological products, we examined the optimization of nutrient supplementation, which has an impact on high-density production of spores by fermentation. Corn steep liquor (CSL) was identified as a lower cost and more effective nutrient source in comparison to conventional nutrient substrates, in particular yeast extract and nutrient broth. The improved sporulation performance of B. cereus could be related to the increased availability of free amino acids, carbohydrates, and minerals in CSL, which had a positive effect on organism growth and sporulation efficiency. The impact of nutrient concentration on spore yield and productivity was modelled to develop a tool for selection of optimal conditions. Excellent correlation with actual laboratory fermentation data was demonstrated. A cost analysis revealed that production using liquid phytase treated and ultra-filtered CSL was less expensive than spray dried CSL and supported cultivation of B. cereus spores at densities higher than 1×1010 CFU ml 1. Adoption of biological agents in commercial applications is lacking, due to limitations in process and product development that address key end user product requirements such as cost, efficacy, shelf life and convenience. The development of suitable spore recovery, drying, formulation and tablet production process steps was thus performed. Key criteria used for downstream process unit evaluation included spore viability, recovery, spore balance closure, spore re-germination, product intermediate stability, end product stability and efficacy. A process flow sheet comprising vertical tube centrifugation, fluidised bed agglomeration and tablet pressing yielded an attractive product. The formulation included corn steep liquor and glucose to enhance subsequent spore re-germination. Viable spore recovery and spore balance closure across each of the process units was high (>70% and >99% respectively), with improvement in recovery possible by adoption of continuous processing at large scale. Spore re-germination was 97%, whilst a product half-life in excess of 5 years was estimated based on thermal resistance curves. The process resulted in a commercially attractive product and affordable variable cost of production. Functionality of the product, incorporating the B. cereus isolate, was investigated across a range of physiological conditions, including salinity, pH and temperature, based on rearing of C. carpio. Temperature had a significant influence on germination, specific growth rate and increase in cell number of B. cereus, whilst salinity and pH did not have any measurable effect on growth. Controlled studies in bioreactors and modelling of the data to the Arrhenius function indicated the existence of high and low growth temperature domains. The rates of pathogenic Aer. hydrophila suppression and decrease in waste ion concentrations (ammonium, nitrite, nitrate and phosphate) were translated into a linear predictive indicator of efficacy of the B. cereus isolate at different temperatures. This study has resulted in development of an upstream and downstream process for production of a new B. cereus isolate (NRRL 100132) which was shown to be safe, stable, functional, robust and cost effective for application in aquaculture.