title: Alginate production and alg8 gene expression by Azotobacter vinelandii in continuous cultures.
abstract: Alginates are polysaccharides that are used as thickening agents, stabilizers, and emulsifiers in various industries. These biopolymers are produced by fermentation with a limited understanding of the processes occurring at the cellular level. The objective of this study was to evaluate the effects of agitation rate and inlet sucrose concentrations (ISC) on alginate production and the expression of the genes encoding for alginate-lyases (algL) and the catalytic subunit of the alginate polymerase complex (alg8) in chemostat cultures of Azotobacter vinelandii ATCC 9046. Increased alginate production (2.4 g l⁻¹) and a higher specific alginate production rate (0.1 g g⁻¹ h⁻¹) were obtained at an ISC of 15 g l⁻¹. Carbon recovery of about 100% was obtained at an ISC of 10 g l⁻¹, whereas it was close to 50% at higher ISCs, suggesting that cells growing at lower sucrose feed rates utilize the carbon source more efficiently. In each of the steady states evaluated, an increase in algL gene expression was not related to a decrease in alginate molecular weight, whereas an increase in the molecular weight of alginate was linked to higher alg8 gene expression, demonstrating a relationship between the alg8 gene and alginate polymerization in A. vinelandii for the first time. The results obtained provide a possible explanation for changes observed in the molecular weight of alginate synthesized and this knowledge can be used to build a recombinant strain able to overexpress alg8 in order to produce alginates with higher molecular weights.
authors.affiliation: Escuela de Ingeniería Bioquímica, Pontificia Universidad Catόlica de Valparaíso, Av. Brasil 2147, Casilla 4059, Valparaíso, Chile. alvaro.diaz@ucv.cl
authors.forename: Alvaro
authors.initials: A
authors.lastname: Díaz-Barrera
authors.forename: Erik
authors.initials: E
authors.lastname: Soto
authors.forename: Claudia
authors.initials: C
authors.lastname: Altamirano
mesh_terms: D000464:Alginates / Q000378:metabolism*; D016948:Azotobacter vinelandii / Q000235:genetics* / Q000378:metabolism*; D019149:Bioreactors; D005285:Fermentation; D015870:Gene Expression; D007218:Industrial Microbiology; D011133:Polysaccharide-Lyases / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism
chemical_list: D000464:Alginates; D013395:Sucrose; D011133:Polysaccharide-Lyases; C016158:poly(beta-D-mannuronate) lyase
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