Development of a bioprocess for the production of an aquaculture biological agent

Lalloo, Rajesh (2010-12)

Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010.

Thesis

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.

AFRIKAANSE OPSOMMING: Biologiese middels bied verskeie maniere om die veelvoudige uitdagings van intensiewe netsgewyse akwakultuur aan te spreek. Gevolglik het ons uitgesoekte Bacillus spesies as potensiële biologiese middels geïsoleer, omdat hierdie groep verskeie biologiese aktiwiteite demonstreer wat van potensiële waarde kan wees in akwakultuur. Die groep toon ook voordele in terme van robuustheid gedurende bioprosessering en eind-toepassings. Natuurlike bakteriële isolate vanuit Cyprinus carpio geassosieerde kultuur omgewings, geselekteer as 'n hoë-waarde model ornamentele spesie, is gesuiwer. Die in vitro doeltreffendheid van die isolate is bepaal gebasseerd op die groei inhibisie van patogeniese Aeromons hydrophila asook die afname in konsentrasies van ammonium, nitriete, nitrate en fosfaat ione wat as tipiese afval produkte gevind word in akwakultuur sisteme. Isolate B001, B002 en B003 is geselekteer op grond van geskiktheid en verder evalueer in in vitro en in vivo proewe met C. carpio. Groei inhibisie van Aer. hydrophila asook 'n afname in konsentrasies van afval ione was tydens die studies gedemonstreer is. Die isolate is identifiseer as Bacillus subtilis, B. cereus en B. licheniformis, respektiewelik, op grond van 16S RNS volgorde homologie. Die hoë volgorde homologie tussen B. subtilis en B. anthracis het verdere veiligheidstudies op die beste isolaat, B. cereus NRRL100132 (B002) genoodsaak. Die isolaat het nie die antraks virulensie plasmied pOX1, pOX2 of die B. cereus enterotoksien getoon nie. Uitklaring van die potensiële meganismes van aksie van biologiese middels fasiliteer 'n begrip van funksionaliteit en moedig tegnologie aanvaarding deur eind-gebruikers aan. Mededingende uitsluiting deur groeitempo en mededingende opname van glukose asook die produksie van siderofore is bewys as sleutel meganismes betrokke in die inhibisie van Aer. hydrophila deur die B. cereus isolaat. Aangesien koste 'n belangrike oorweging is in die ontwikkeling van kommersiële toepaslike biologiese produkte, is die optimisering van voedingstof aanvullings wat 'n impak het op hoëdigtheid produksie van spore deur fermentasie ondersoek. Week-vloeistof van mielie prosessering (CSL) is identifiseer as 'n lae koste en effektiewe voedingsbron in vergelyking met konvensionele voeding substrate, veral gisekstrak en voedingsboeljon. Die verbeterde sporulering prestasie van B. cereus kon toegeskryf word aan die verhoogde beskikbaarheid van vrye aminosure, koolhidrate en minerale in CSL, wat 'n postitewe effek op organisme groei en sporulerings effektiwiteit getoon het. Die impak van voedingstof konsentrasie op spoor opbrengs en produktiwiteit is gemodelleer om 'n werktuig vir die selektering van optimale kondisies te ontwikkel. Uitstekende korrelasie met werklike laboratorium data is gedemonstreer. Koste analises het getoon dat produksie deur middel van vloeibare fitase-behandelde en ultra-filtreerde CSL goedkoper is as sproei-gedroogde CSL en ondersteun verder die kultivering van B. cereus spore teen digthede hoër as 1 x 1010 kolonie vormende eenhede.ml-1. Die opname van biologiese middels in kommersiële toepassings skiet tekort as gevolg van beperkinge in proses en produk ontwikkeling wat belangrike eind-gebruiker vereistes soos koste, doeltreffendheid, rak leeftyd en gerieflikheid aanspreek. Die ontwikkeling van toepaslike prosesse vir spoor herwinning, droging, formulering en tablet produksie is gevolglik uitgevoer. Belangrike maatstawwe wat gebruik is vir stroomaf proseseenheid-ontwikkeling het lewensvatbaarheid, herwinning, spoor balans sluiting, spoor her-ontkieming, intermediêre produk stabiliteit, eindproduk stabiliteit en doeltreffendheid ingesluit. 'n Proses vloeidiagram bestaande uit vertikale buis sentrifugasie, vloeibare bed agglomerasie en tablet persing het 'n aantreklike produk voortgebring. Die formulering het ook CSL en glukose ingesluit om gevolglike spoor herontkieming te verbeter. Lewensvatbare spoor herwinning en spoor balans sluiting oor elke proses eenheid was hoog (>70% en 99% respektiewelik) met verbetering in herwinning wat moontlik gemaak is deur die gebruik van aaneenlopende prosessering op groot skaal. Spoor her-ontkieming was 97%, terwyl produk halfleeftyd langer as 5 jaar beraam is, gebasseer op termiese weerstand grafieke. Die proses het gelei tot 'n kommersiële aantreklike produk asook bekostigbare veranderbare produksie koste. Die funksionaliteit van die tablet-produk met die ingeslote B. cereus isolaat is ondersoek oor 'n reeks fisiologiese kondisies insluitend soutgehalte, pH en temperatuur, gebasseer op die kultivering van C. carpio. Temperatuur het 'n betreklike invloed op ontkieming, spesifieke groeitempo en toename in sel hoeveelheid van B. cereus gehad, terwyl soutgehalte en pH nie enige meetbare effek op groei gehad het nie. Gekontrolleerde studies in bioreaktors en modellering van die data op die Arrhenius funksie het hoë en lae groei temperatuur domeins gewys. Die tempo van patogeniese Aer. hydrophila onderdrukking en afname in konsentrasies van afval-ione (ammonium, nitriete, nitrate en fosfaat) is herlei na 'n liniêre voorspellende aanwysing van effektiwiteit van B. cereus isolate by verskillende temperature. Die studie het gelei tot die ontwikkeling van stroomop- en stroomaf-prosesse vir die produksie van 'n nuwe B. cereus isolaat (NRRL 100132) wat bewys is as veilig, stabiel, funksioneel, robuust en koste effektiewe vir toepassing in akwakultuur.

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