Biosynthesis of Alginate and Poly(3-Hydroxybutyrate) by the Bacterial Strain Azotobacter agile 12

Abstract

The ability of Azotobacter agile 12 to produce the polymers alginate (ALG) and poly(3-hydroxybutyrate) (PHB) and their physicochemical properties is studied in the work. It was shown that the strain A. agile 12 produces ALG and PHB simultaneously, thought predominantly ALG, under the conditions of high aeration levels. Infrared spectroscopy of bacterial ALG showed a prevalence of mannuronic over guluronic residues (M/G = 70/30) in the polymer chain and the presence of acetyl groups on the mannuronic monomers. No acetyl groups were found in seaweed ALG. Infrared spectroscopy showed that PHB is characterized by an absorption band in the region 1760 cm^–1. The chemical nature of PHB as a homopolymer consisting of resides of 3-hydroxybutyric acid was confirmed by ¹H-NMR analysis. The thermal behavior of bacterial ALG by thermogravimetric analysis is characterized by three stages (dehydration, first decomposition, and second decomposition). In contrast to ALG, PHB had only one stage of decomposition with a prior very low mass loss (1.25%) at the dehydration stage. The water absorption test showed that bacterial ALG has a higher capacity for water absorption in comparison with seaweed ALG, whereas PHB is a hydrophobic polymer. Thus, PHB and ALG synthesized simultaneously by A. agile 12 differ in their physicochemical properties: PHB is a hydrophobic, thermoplastic, mechanically strong polyester, while alginate is hydrophilic, hydrogel-forming, temperature unstable, elastic and mechanically destructible polysaccharide.