微囊藻胶鞘多糖和水溶性胞外多糖的化学特性

Chemical characteristics of capsular polysaccharide and water-soluble released exopolysaccharide from Microcystis

微囊藻（Microcystis）产生大量胞外多糖（EPS）,包括包裹在细胞外的胶鞘多糖（CPS）和释放到周围环境中的水溶性多糖（RPS）.为探究EPS在蓝藻水华发生中的生理生态学意义,迫切需要了解微囊藻EPS的化学特性.本文从太湖分离群体微囊藻,经过大约18个月实验室培养后,其中一些藻株转变为单细胞形态.选择5株群体藻和4株单细胞藻,比较分析这些藻株EPS的化学特性发现：（1）所有9株藻的EPS均为含有脱氧己糖的酸性杂多糖;（2）所有9株藻的CPS的糖醛酸含量（1.2%～2.1%）均低于RPS的糖醛酸含量（2.4%～6.2%）;（3）所有9株藻的EPS均含有乙酰基和硫酸基,其中,每一株藻CPS的乙酰基含量均高于RPS的乙酰基含量,所有群体藻CPS的乙酰基含量（4.1%～6.6%）高于所有单细胞藻CPS的乙酰基含量（2.0%～3.2%）.本文进而讨论了EPS化学特性对EPS水溶性和微囊藻群体形成的影响,以及对其生态学作用的影响.在这些化学特性中,乙酰取代基团被认为可能是影响微囊藻EPS生理生态学作用的重要因素.

Microcystis spp. produces large amounts of exopolysaccharides （EPSs） including capsular polysaccharides （CPSs） which form mucilaginous matrix around the cells, and water-soluble released polysaccharides （RPSs）. To understand their eco- physiological roles in cyanobacterial bloom, we urgently need more information on chemical characters of EPS. In this paper, colo- nial Microcystis strains were isolated from Lake Taihu. After incubation for about 18 months in the lab, some strains turned to be u- nicellular form. The comparative study of chemical characteristics of EPSs from five colonial strains and four unicellular strains showed that （ 1 ） all the EPSs were acidic heteropolysaccharides containing the deoxyhexoses; （2） the uronic acid content was low- er in CPS （ 1.2% -2. 1% ） than in RPS （ 2.4% -5.2% ） for all Microcystis strains ; （ 3 ） acetate and sulfate groups were present in all EPSs, of which the acetate content was higher in CPS than in RPS for each strain, and higher in CPSs （4. 1%-6. 6% ） of all colonial strains than in CPSs （ 2.0% -3.2% ） of all unicellular strains. The chemical characteristics of EPS were discussed with re- spects in the solubility of EPS in water, the roles in colony formation and the ecological roles in the aquatic environments. It was thought that among these chemical characteristics, acetyl substitution might be an important factor affecting the ecophysiological roles of EPS in cyanobacterial bloom.