镉对稻田土壤典型微生物种的胁迫生理毒性

Physiological toxicity of Cd^(2+) to representative microbial species in submerged paddy soil

以水稻田土壤中典型的单种微生物为实验材料,采用纯培养方法,从个体水平上全面探讨了重金属镉胁迫对稻田土壤典型微生物的的生长、活性以及生化过程的生理毒性影响。研究表明:不同微生物纯培养对镉胁迫的敏感程度不同,G+较G-对Cd2+更为敏感,表现为世代时间缩短,最高菌浓度下降。固氮菌对Cd2+非常敏感,当Cd2+质量浓度为0.2mg·L-1时即完全抑制菌体增殖。同时,外源镉强烈的抑制作为稻田土壤中功能微生物的厌氧固氮菌及产甲烷细菌的生物活性,各菌种镉胁迫下细菌细胞内可溶性蛋白、还原糖、核酸质量浓度都在低质量浓度镉胁迫时有所增加;随着镉质量浓度的增加,细菌细胞内各种物质的质量浓度开始减小,以减慢细胞代谢速度,增强对镉胁迫的适应力;各种物质的质量浓度变化趋势为可溶性蛋白>还原糖>核酸,R.eutrophaDKC1细胞内含物质量浓度基本保持稳定。结果可在一定程度上说明镉对微生物的毒性效应,且能在早期较灵敏地指示污染的影响,作为稻田土壤环境受到污染胁迫的细胞生化指标具有一定可行性。

The physiological toxicity of Cd^2＋ to the representative microbial species in submerged paddy soil was studied by the pure culture method. It is showed that G^＋ bacteria were more remarkably affected by cadmium than G^- bacteria, and the shorter generation time and the lower growth density of G^＋ bacteria. The nitrogen-fixing bacteria were more sensitive to Cd^2＋, which was inhabited even when the cadmium content attained to 0.2 mg·L^-1. Meantime, cadmium intensively inhabits the activities of nitrogen-fixing bacteria and the methanogenic bacteria, both of which were the functional microorganisms in the paddy soil. Microorganisms need to adjust their biochemical process inside cell to adapt the new environment when exposed to cadmium. The contents of the soluble protein, the reducing sugar and nucleic acid inside cells would be increased at the low concentration of cadmium, but decreased with the increase of that to slow the rate of cell metabolism and suit the stress of cadmium. The order of content change being sensitive to cadmium was as follows： soluble protein 〉 reducing sugar 〉 nucleic acid. Therefore, the result could explain the physiological toxicity of the representative microbial species from Cd^2＋. It is feasible to be used as cell biochemical index to indicate the Cd contamination.