Molecular weight and viscosifying power of alginates produced by mutant strains of Azotobacter vinelandii under microaerophilic conditions

Andres García,Tania Castillo,Diego Ramos,Carlos L Ahumada-Manuel,Cinthia Núñez,Enrique Galindo,Jochen Büchs,Carlos Peña

doi:10.1016/j.btre.2020.e00436

Abstract

Alginates are polysaccharides that are of interest in various industrial applications. This is due to the viscosifying properties of alginates, which depends on the weight-average molecular weight. The aim of the present study was to evaluate the changes in alginate quality, in terms of the viscosifying power and weight-average molecular weight of the polymer produced by Azotobacter vinelandii mutant strains in shake flasks under microaerophilic conditions. In cultures developed at oxygen transfer rate (OTR) values close to 5 mmol L−1 h−1, the highest viscosifying power (1.75 L g−1) and weight-average molecular weight (3112 ± 150 kDa) were achieved in cultures performed with the AT9 strain. These values were higher than those obtained for the alginates produced by the parental strain ATCC 9046 grown under similar OTR conditions. In contrast, the alginate produced by the GG9 and OPAlgU + exhibited a very low weight-average molecular weight and therefore a poor viscosifying power. Our results have shown that by the cultivation of AT9 strain under microaerophilic conditions it is possible to obtain a polymer having a high weight-average molecular weight and excellent viscosifying capacity. Therefore, it could be a viable strategy for producing alginates for industrial applications.

Highlights

Alginates are biopolymers containing β-D-mannuronic acid (M) and α-L-guluronic (G) acid monomers that are produced by bacterial species such as Azotobacter vinelandii
The aim of this study was to evaluate the viscosifying power and weight-average molecular weight of alginates synthesized by A. vinelandii mutant strains under microaerophilic conditions and no-nitrogen fixation
Considering the high mean molecular mass that the absence of MucG conferred to the alginate produced by mutant GG9, we wanted to explore this effect in the background of strain ATCC 9046, which is a natural alginate over-producing strain of A. vinelandii

Summary

Introduction

Alginates are biopolymers containing β-D-mannuronic acid (M) and α-L-guluronic (G) acid monomers that are produced by bacterial species such as Azotobacter vinelandii. These polymers have gel-forming and viscosifying properties, besides, they are characterized by their non-antigenicity, biocompatibility and biodegradability [1,2]. [1,3,4,5] Both the alginate composition (MG/ratio) and its weightaverage molecular weight influence the functional properties of the polymer [2,6]. In this regard, the viscosity and gelling properties, including the pre-gel solution viscosity and post-. It is suitable to obtain polymers with an appropriate molecular weight for specific commercial applications, either as viscosifying or gelling agents

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Results