Rehm B H, Valla S
Institut für Mikrobiologie der Westfälischen Wilhelms-Universität Münster, Germany.
Appl Microbiol Biotechnol. 1997 Sep;48(3):281-8. doi: 10.1007/s002530051051.
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.
藻酸盐是β-D-甘露糖醛酸和α-L-古洛糖醛酸（GulA）通过1-4键连接而成的共聚物。这种聚合物是一种成熟的工业产品，可通过收获褐藻商业获得。一些细菌，主要来源于假单胞菌属，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。尽管聚合过程的生物化学仍知之甚少，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、调控和生物化学已得到特别充分的表征。在过去3年中，也报道了棕色固氮菌中藻酸盐生物合成分子遗传学的主要方面。在这两种生物体中，聚合的直接前体都是GDP-甘露糖醛酸，该化合物中的糖残基聚合成甘露糖醛酸聚糖。然后，这种均匀的聚合物通过O-2和/或O-3位的乙酰化以及一些残基的差向异构化进一步修饰，导致乙酰基和GulA残基的含量可变。相比之下，海藻藻酸盐不被乙酰化。棕色固氮菌中差向异构化步骤的性质比铜绿假单胞菌中更复杂，而藻酸盐生物合成的生物化学和遗传学的其他方面似乎相似。GulA残基的含量和分布强烈影响藻酸盐的物理化学性质，因此从应用的角度来看，差向异构化过程非常有趣。本文综述了我们目前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认识。
