記者近日從中科院水保所獲悉，該所青年科研人員方臨川結(jié)合宏觀吸附實驗和等溫滴定微量熱,、X射線吸收精細結(jié)構(gòu)等多種現(xiàn)代儀器分析技術,，在分子水平上揭示了土壤中細菌分泌的胞外聚合物（EPS）與針鐵礦的作用過程和機理。該研究對揭示土壤的本質(zhì),，合理調(diào)節(jié)土壤生物活性,，闡明細菌黏附、生物膜形成和功能機制以及污染物的遷移分布等具有重要的理論和實際意義,。
據(jù)了解,，在自然界土壤中,，80%～90%的微生物黏附在各種礦物或礦物—有機物復合體表面,，形成單個的微菌落或生物膜,。在形成生物膜之前，細菌分泌的胞外聚合物首先在土壤固相表面形成“條件膜”,，以調(diào)控細菌的黏附和遷移,，進而影響生物膜的結(jié)構(gòu)和功能。
方臨川研究發(fā)現(xiàn),，細菌分泌的胞外聚合物組分中蛋白質(zhì),、核酸等大分子物質(zhì)中的含磷基團與針鐵礦表面羥基配位形成內(nèi)圈絡合物，且吸附產(chǎn)物結(jié)構(gòu)與體系pH有密切關聯(lián)。低pH時（pH為3.0），磷酸基團僅有一個去質(zhì)子化的含氧陰離子直接和針鐵礦表面的FeOH1/2-基團結(jié)合形成單齒絡合物,；而在高pH時（pH為9.0），磷酸鹽基團中有2個含氧陰離子和針鐵礦表面的2個FeOH1/2-基團結(jié)合形成雙齒絡合物,。同時，體系pH由低到高時（3.0～9.0）,，吸附產(chǎn)物構(gòu)型由單基配位向雙基配位過渡,，從而揭示出體系pH通過影響溶液中EPS-P中磷酸根質(zhì)子解離和締合，為導致吸附產(chǎn)物構(gòu)型變化的重要原因,。
該結(jié)果表明,，土壤中微生物與礦物相互作用的過程中可能存在某種分子識別機制，細菌分泌的胞外聚合物與針鐵礦之間P-O-Fe鍵的形成對于細菌黏附和生物膜的形成具有重要調(diào)控作用,。(生物谷Bioon.com)
10.1016/j.watres.2012.07.046,
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Reactions between bacterial exopolymers and goethite: A combined macroscopic and spectroscopic investigation
Linchuan Fang, Yuanyuan Cao, Qiaoyun Huang, Sharon L. Walker, Peng Cai
The adsorption to goethite of extracellular polymeric substances (EPS) isolated from Pseudomonas putida was investigated using batch adsorption experiments, electrophoretic mobility (EM) measurements, Fourier transform infrared (FTIR) spectroscopy, isothermal titration calorimetry (ITC) and X-ray absorption fine structure (XAFS) spectroscopy. The adsorption of EPS decreased the point of zero charge of goethite from 7.6 to 3.2, suggesting the formation of negatively charged inner-sphere surface complexes. The adsorption isotherms of EPS on goethite conformed to the Langmuir equation. The adsorption energy constant (K) of EPS on goethite was in the sequence of EPS phosphate-containing moieties > nitrogen-containing moieties > carbon-containing moieties, indicating those containing phosphate were the most strongly adsorbed. FTIR showed ligand exchange of phosphate groups of EPS with surface hydroxyls on goethite. Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy results further demonstrated phosphate groups of EPS can form monodentate inner-sphere complexes at lower pH 3.0, while form bidentate inner-sphere complexes at higher pH 9.0. The oxidation state of iron in goethite was not changed after the reaction with EPS at different pH values. The information obtained in this study is of fundamental significance for the understanding of the interaction mechanisms between bacteria and minerals in soil and aquatic environments.
