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Bacterial alginates: biosynthesis and applications

机译：细菌藻酸盐：生物合成与应用

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摘要

Alginate is a copolymer of beta-D-mannuronic acid and alpha-L-guluronic acid (GulA), linked together by 1-4 linkages. The polymer is a well-established industrial product obtained commercially by harvesting brown seaweeds. Some bacteria, mostly derived from the genus Pseudomonas and belonging to the RNA superfamily I, are also capable of producing copious amounts of this polymer as an exopolysaccharide. The molecular genetics, regulation and biochemistry of alginate biosynthesis have been particularly well characterized in the opportunistic human pathogen Pseudomonas aeruginosa, although the biochemistry of the polymerization process is still poorly understood. In the last 3 years major aspects of the molecular genetics of alginate biosynthesis in Azotobacter vinelandii have also been reported. In both organisms the immediate precursor of polymerization is GDP-mannuronic acid, and the sugar residues in this compound are polymerized into mannuronan. This uniform polymer is then further modified by acetylation at positions O-2 and/or O-3 and by epimerization of some of the residues, leading to a variable content of acetyl groups and GulA residues. In contrast, seaweed alginates are not acetylated. The nature of the epimerization steps are more complex in A. vinelandii than in P. aeruginosa, while other aspects of the biochemistry and genetics of alginate biosynthesis appear to be similar. The GulA residue content and distribution strongly affect the physicochemical properties of alginates, and the epimerization process is therefore of great interest from an applied point of view. This article presents a survey of our current knowledge of the molecular genetics and biochemistry of bacterial alginate biosynthesis, as well as of the biotechnological potential of such polymers.
机译：海藻酸盐是β-D-甘露糖醛酸和α-L-古洛糖醛酸（GulA）的共聚物，它们通过1-4个键连接在一起。该聚合物是一种成熟的工业产品，可通过收获棕色海藻从商业上获得。一些细菌，大多数来源于假单胞菌属，属于RNA超家族I，也能够产生大量这种聚合物作为胞外多糖。尽管对聚合过程的生物化学知之甚少，但在机会性人类病原体铜绿假单胞菌中，藻酸盐生物合成的分子遗传学，调控和生物化学已经得到了很好的表征。在最近的三年中，也已经报道了葡萄固氮藻中藻酸盐生物合成的分子遗传学的主要方面。在这两种生物中，直接聚合的前体是GDP-甘露糖醛酸，该化合物中的糖残基被聚合成甘露糖醛酸。然后，通过在位置O-2和/或O-3处进行乙酰化并通过某些残基的差向异构化，对该均匀的聚合物进行进一步修饰，从而导致乙酰基和GulA残基的含量变化。相反，海藻藻酸盐未乙酰化。与铜绿假单胞菌相比，A。vinelandii中差向异构化步骤的性质更为复杂，而藻酸盐生物合成的其他生物化学和遗传学方面似乎相似。 GulA残基的含量和分布强烈影响藻酸盐的物理化学性质，因此从应用的观点来看，差向异构化过程引起了极大的兴趣。本文介绍了我们对细菌藻酸盐生物合成的分子遗传学和生物化学以及此类聚合物的生物技术潜力的最新了解。

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