Asiri, Fahad (2021-12). Sustainable Production of Biodegradable Biopolymers and their Applications in Support of Organic Aquaculture. Doctoral Dissertation.
Thesis
Polyhydroxyalkanoates (PHA) are a class of microbially-produced biodegradable biopolymers obtained from renewable feedstocks. Due to variations in the properties of PHA, they have received growing attention to develop several practical applications, particularly bioplastics. Recently, a common PHA type, poly(3-hydroxybutyrate) (PHB), has been identified as an effective biocontrol agent to replace antibiotics and improve growth and disease resistance in aquaculture. However, the production and application of PHB are associated with several challenges, such as expensive feedstocks, costly sterilization, high-energy input harvesting techniques, and toxic extraction and purification processes. The overall goal of this three-manuscript dissertation was to establish a sustainable and economical process for PHB production, which in turn, can be applied as an effective biocontrol agent and aquafeed. The implications of this process can overcome the traditional PHB challenges, as well as challenges associated with commercial aquaculture, such as waste management, high feed cost, and the use of antibiotics to control pathogens. In paper I, a novel PHB production and supplementation system, called recirculating aquaculture system for PHB-rich microorganisms (RASPHB), was developed. This system integrates the treatment of agro-industrial wastes, including aquaculture wastewater/wastes, with the production and harvest of PHB-rich Zobellella denitrificans ZD1 (designated as ZD1 hereafter) using chitosan as a biocoagulant. In paper II, chitosan-harvested PHB-rich ZD1 demonstrated multifunctional effects, such as improving growth, survival, immune response, and altering gut microbiome in an aquaculture animal model, brine shrimp Artemia. In paper III, results showed the effects of providing different agro-industrial wastes/wastewaters as substrates on PHA polymer composition in ZD1. Furthermore, bacterial cells that accumulated fractions of longer PHA monomers, along with PHB, magnified the biocontrol efficacy by enhancing antipathogenic properties, providing additional energy to Artemia, and improving survival against pathogens. Overall, the engineering approach of PHB production and application, proposed in this dissertation, yields promising potentials toward sustainable PHB production and organic aquaculture practices to enhance commercial production.
