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

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.

SUBMITTER: Garcia A

PROVIDER: S-EPMC7049565 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Molecular weight and viscosifying power of alginates produced by mutant strains of <i>Azotobacter vinelandii</i> under microaerophilic conditions.

García Andres A Castillo Tania T Ramos Diego D Ahumada-Manuel Carlos L CL Núñez Cinthia C Galindo Enrique E Büchs Jochen J Peña Carlos C

Biotechnology reports (Amsterdam, Netherlands) 20200220

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 <i>Azotobacter vinelandii</i> mutant strains in shake flasks under microaerophilic conditions. In cultures developed at oxygen ...[more]

PMID: 32140445

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Project description:Azotobacter vinelandii produces the linear exopolysaccharide alginate, a compound of significant biotechnological importance. The biosynthesis of alginate in A. vinelandii and Pseudomonas aeruginosa has several similarities but is regulated somewhat differently in the two microbes. Here, we show that the second messenger cyclic dimeric GMP (c-di-GMP) regulates the production and the molecular mass of alginate in A. vinelandii The hybrid protein MucG, containing conserved GGDEF and EAL domains and N-terminal HAMP and PAS domains, behaved as a c-di-GMP phosphodiesterase (PDE). This activity was found to negatively affect the amount and molecular mass of the polysaccharide formed. On the other hand, among the diguanylate cyclases (DGCs) present in A. vinelandii, AvGReg, a globin-coupled sensor (GCS) DGC that directly binds to oxygen, was identified as the main c-di-GMP-synthesizing contributor to alginate production. Overproduction of AvGReg in the parental strain phenocopied a ΔmucG strain with regard to alginate production and the molecular mass of the polymer. MucG was previously shown to prevent the synthesis of high-molecular-mass alginates in response to reduced oxygen transfer rates (OTRs). In this work, we show that cultures exposed to reduced OTRs accumulated higher levels of c-di-GMP; this finding strongly suggests that at least one of the molecular mechanisms involved in modulation of alginate production and molecular mass by oxygen depends on a c-di-GMP signaling module that includes the PAS domain-containing PDE MucG and the GCS DGC AvGReg.IMPORTANCE c-di-GMP has been widely recognized for its essential role in the production of exopolysaccharides in bacteria, such as alginate produced by Pseudomonas and Azotobacter spp. This study reveals that the levels of c-di-GMP also affect the physical properties of alginate, favoring the production of high-molecular-mass alginates in response to lower OTRs. This finding opens up new alternatives for the design of tailor-made alginates for biotechnological applications.

Dataset Information

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

Publications

Molecular weight and viscosifying power of alginates produced by mutant strains of <i>Azotobacter vinelandii</i> under microaerophilic conditions.

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