Escuela de Ingeniería Bioquímica, Pontificia Universidad Catόlica de Valparaíso, Av. Brasil 2147, Casilla 4059, Valparaíso, Chile.
J Ind Microbiol Biotechnol. 2012 Apr;39(4):613-21. doi: 10.1007/s10295-011-1055-z. Epub 2011 Nov 10.
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.
藻酸盐是多糖，在许多行业中用作增稠剂、稳定剂和乳化剂。这些生物聚合物是通过发酵生产的，但对细胞水平上发生的过程的了解有限。本研究的目的是评估搅拌速度和入口蔗糖浓度（ISC）对固氮菌（Azotobacter vinelandii ATCC 9046）恒化培养中藻酸盐生产和编码藻酸盐裂解酶（algL）和藻酸盐聚合酶复合物催化亚基（alg8）基因表达的影响。在 ISC 为 15 g l⁻¹时，藻酸盐产量增加（2.4 g l⁻¹），比产率更高（0.1 g g⁻¹ h⁻¹）。ISC 为 10 g l⁻¹时，碳回收率约为 100%，而在较高 ISC 时接近 50%，这表明在较低蔗糖进料速率下生长的细胞更有效地利用碳源。在所评估的每个稳定状态下，algL 基因表达的增加与藻酸盐分子量的降低无关，而藻酸盐分子量的增加与 alg8 基因表达的增加有关，这首次证明了 alg8 基因与固氮菌中藻酸盐聚合之间存在关系。所获得的结果为观察到的藻酸盐合成分子量变化提供了可能的解释，并且该知识可用于构建能够过表达 alg8 的重组菌株，以生产具有更高分子量的藻酸盐。
