海洋细菌Agarivorans sp.HZ105的琼胶降解酶系

The Agar-degrading Enzymatic System of Marine Bacterium Agarivorans sp.HZ105

通过克隆得到菌株Agarivorans sp.HZ105中3个琼胶酶基因,长度分别为2 988 bp、1 437 bp和1 362 bp,分别编码琼胶酶HZ1、HZ3和HZ4,分别属于糖苷水解酶GH50、GH118和GH16家族。将这些琼胶酶基因与质粒p ET-32(a)构建重组表达载体,转化大肠杆菌BL21(DE3),实现了琼胶酶基因的重组原核表达,制备了重组酶,研究了琼胶酶的酶解产物。琼胶酶HZ1降解琼脂糖以及高聚合度新琼寡糖(聚合度为8、10、12和14)得到新琼二糖和新琼四糖;琼胶酶HZ3降解琼脂糖的终产物是高聚合度新琼寡糖;琼胶酶HZ4降解琼脂糖和高聚合度新琼寡糖为新琼四糖和新琼六糖。因此推测菌株HZ105主要先用琼胶酶HZ3和HZ4降解琼脂糖为较高聚合度的新琼寡糖,随后这些寡糖被琼胶酶HZ1和HZ2(课题组先前报道的另一个琼胶酶)降解为低聚合度新琼寡糖。首次研究报道了Agarivorans属中能产生4个琼胶酶的细菌菌株及其琼胶降解酶系,丰富了有关细菌降解琼胶酶体系及其中各琼胶酶作用的研究和认识,也有利于菌株HZ105琼胶酶的有效开发应用。

Three agarase genes（hz1,hz2,hz3）of 2 988 bp, 1 437 bp and 1 362 bp respectively, were cloned from strainAgarivorans sp.HZ105. These three agarase genes（hz1,hz2,hz3）encoded agarase HZ1, HZ3 and HZ4 and belonged to glycoside hydrolase family GH50, GH118 and GH16, respectively. The agarase genes of strain HZ105 were linked with vector pET-32a（＋）and then were transfered toEscherichia coliBL21（DE3）. These agarase genes were successfully expressed inE. coli cells and their recombinant agarases were prepared. Agarose degradations of the recombinant agarases were studied. Agarase HZ1 could degrade agarose and neoagarooligosaccharides with high degrees of polymerization（8, 10, 12 and 14）into neoagarobiose and neoagarotetraose. Agarase HZ3 digested agarose to produce neoagarooligosaccharides with high degrees of polymerization, while agarase HZ4 decomposed agarose and neoagarooligosaccharides with high degrees of polymerization to yield neoagarotetraose and neoagarohexaose. Therefore, strain HZ105 might produce firstly agarases HZ3 and HZ4 to degrade agarose into neoagarooligosaccharides with high degrees of polymerization, and the products of agarases HZ3 and HZ4 would be then digested into neoagarooligosaccharides with low degrees of polymerization by agarase HZ1 and another agarase（HZ2）from strain HZ105 reported previously by our research group. Strain HZ105 is the first reported strain that produces four agarases and this study is the first report of the agar-degrading enzymatic system in the genusAgarivorans. The results could enrich the knowledge about the bacterial agar-degrading enzymatic system and the roles of the agarases in the system. The application of agarases from strain HZ105 should also benift from this study.