Development of novel microalgal and bacterial based production platforms

The use of expression platforms is a critical aspect of biotechnology, enabling the production of proteins, enzymes and other molecules by introducing a gene of interest into a chosen expression host. Commonly used expression systems include bacterial, yeast, mammalian, plant and algal. Here we focus on the use of bacterial and microalgal expression systems specifically for the production of both proteins and double-stranded RNA (dsRNA). The initial focus of this research was to establish a novel, microalgal-based, cost effective approach for shrimp disease control in South East Asia. This project utilised the microalgae C. reinhardtii, engineered to express two dsRNAs targeting the shrimp pathogen White Spot Syndrome Virus (WSSV), which was then incorporated into the shrimp feed. This feed was tested for its effectiveness in WSSV challenge trials. The results from these trials were inconclusive regarding its effectiveness as they showed no clear benefit of feeding WSSV specific dsRNA over the control dsRNA. However, the utilisation of this technology presents promising avenues for further exploration and development as it does not require downstream processing and purification prior to feeding. The second chapter aimed to express antibodies in C. reinhardtii to be used as an effective management tool for Vibrio control in shrimp. Expression and purification were achieved, with further testing required to measure its effectiveness in shrimp as a whole-cell feed. The third chapter aimed to express a fragment fusion protein in E. coli for use as a subunit vaccine in grouper fish for V. parahaemolyticus control. This fusion protein was used to vaccinate grouper fish and results highlighted it as a promising candidate for future experiments. Finally, the expression of the plastic degrading enzyme; PETase was successfully achieved in E. coli at both shake flask and batch fed fermentation scales. The protein was also successful purified and activity was confirmed through PET breakdown analysis using HPLC, demonstrating its efficacy in degrading polyethylene terephthalate (PET).