Bioprocess Design: Fermentation Strategies for Improving the Production of Alginate and Poly-β-Hydroxyalkanoates (PHAs) by Azotobacter vinelandii

Abstract

Industrial interest in microbial polymers has been stimulated by their unique properties and the opportunity to develop new materials, which can be used for specific applications in medical and pharmaceutical industries. Azotobacter vinelandii produces two polymers of biotechnological importance; alginate, an extracellular polysaccharide, and poly-┚hydroxybutyrate (PHB), an intracellular polyester of the polyhydroxyalkanoates (PHAs) family (Galindo et al., 2007). Alginates are linear polysaccharides composed of variable amounts of (1–4)-┚-D-mannuronic acid and its epimer, ┙-L-guluronic acid. Alginates present a wide range of applications, acting as stabilizing, thickening, gel or film-forming agents, in various industrial fields. Currently, new applications are being discovered for these polymers, such as their use as a source of soluble fiber, or in medical products. One example is found in the use of alginate gel beads as entrapment devices for transplantation of e. g. insulin producing cells and tissue engineering (Hernandez et al., 2010). The intracellular polyester PHB and other PHAs have been drawing attention because they are biodegradable and biocompatible thermoplastics, which can be processed to create a wide variety of consumer products, including plastics, films, and fibers (Aldor & Keasling, 2003). Recently, and based on their properties of biocompatibility and biodegradability, new attractive applications for PHAs have been proposed in the medical field, where the chemical composition and product purity are critical (Williams & Martin, 2005). The subjects covered in this chapter include research concerning the production of alginate and PHB by A. vinelandii, particularly the molecular regulation of the production of these polymers, the influence of fermentation parameters on the production and composition of alginate and PHB, some reports about the scaling-up of the process and downstream processing, and finally, novel fermentation strategies that could be applied for the production of alginate and PHAs by A. vinelandii.