Effect of Different Sucrose Concentrations on the Biosynthesis of Poly(3-Hydroxybutyrate) and Alginate by the Bacterial Strain Azotobacter Vinelandii 12 under Different Aeration Conditions

Bacteria of the genus Azotobacter sp. produce two classes of biologically important biocompatible and biodegradable polymers, polyoxyalkanoates, which are the bacterial reserve, and alginates (ALG), which perform the function of protecting nitrogenase from oxygen. Both polymers are becoming increasingly important for use in bioengineering, pharmaceuticals, and medicine, so studies of their biosynthesis and properties are currently highly relevant. The present work shows the possibility of regulating alginate and poly(3-hydroxybutyrate) (PHB) synthesis by a culture of A. vinelandii 12 depending on the increase in the sucrose concentration in the medium under different aeration conditions. At high aeration and high sucrose concentrations in the medium (50 g/L), the maximum yield of free (1.08 g/L) and capsular ALG (2.26 g/L) in the medium was obtained. Under low aeration conditions, the synthesis of free ALG was completely inhibited. The maximum value of РНB synthesis was observed at medium aeration and a high concentration of sucrose (50 g/L) in the medium. The maximum molecular weight (MW) of ALG was 477 kDa, while the maximum MW of PHB was much higher, reaching 1479 kDa. At low sucrose concentrations in the medium (5 to 20 g/L), capsular ALG is predominantly synthesized (up to 100% of the sum of all polymers) at all aeration levels. With increasing sucrose concentration, PHB is predominantly synthesized (68%) under low aeration conditions, an equal ratio of PHB and capsular ALG synthesis is observed under medium aeration conditions, and free ALG is actively synthesized under high aeration conditions. This work demonstrates the possibility of obtaining a selective synthesis of ALG or PHB by A. vinelandii 12 by modifying its cultivation conditions. The results obtained can be used for the development of directed biosynthesis of target products (PHB and ALG) in biotechnology.