Characterization of a Sinorhizobium Isolate and Its Extracellular Polymer Implicated in Pollutant Transport in Soil

A bacterium isolated from soil (designated 9702-M4) synthesizes an extracellular polymer that facilitates the transport of such hydrophobic pollutants as polynuclear aromatic hydrocarbons, as well as the toxic metals lead and cadmium in soil. Biolog analysis, growth rate determinations, and percent G+C content identify 9702-M4 as a strain of Sinorhizobium meliloti. Sequence analysis of a 16S rDNA fragment gives 9702-M4 a phylogenetic designation most closely related to Sinorhizobium fredii. The extracellular polymer of isolate 9702-M4 is composed of both an extracellular polysaccharide (EPS) and a rough lipopolysaccharide. The EPS component is composed mainly of 4-glucose linkages with monomers of galactose, mannose, and glucuronic acid and has pyruval and acetyl constituents. The lipid fraction and the negative charge associated with carbonyl groups of the exopolymer are thought to account for the binding of polynuclear aromatic hydrocarbons and cationic metals.

从土壤中分离得到的编号为9702-M4的细菌，可合成一种胞外聚合物，该聚合物能够促进多环芳烃等疏水性污染物，以及土壤中有毒重金属铅、镉的转运。通过Biolog分析、生长速率测定以及G+C摩尔百分比含量分析，确定9702-M4为草木樨中华根瘤菌（Sinorhizobium meliloti）的一株菌株。对16S rDNA片段的序列分析结果显示，9702-M4的系统发育分类地位与费氏中华根瘤菌（Sinorhizobium fredii）最为接近。该分离株9702-M4的胞外聚合物由胞外多糖（extracellular polysaccharide, EPS）和粗糙型脂多糖共同组成。该胞外多糖组分主要以1,4-葡萄糖苷键连接，单糖组分为半乳糖、甘露糖及葡萄糖醛酸，并含有丙酮酰基与乙酰基取代基。研究认为，该胞外聚合物的脂质组分以及其羰基基团所携带的负电荷，是其结合多环芳烃与阳离子重金属的关键机制。