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(guān)吸附實(shí)驗(yàn)和等溫滴定微量熱、X射線(xiàn)吸收精細(xì)結(jié)構(gòu)等多種現(xiàn)代儀器分析技術(shù),，在分子水平上揭示了土壤中細(xì)菌分泌的胞外聚合物（EPS）與針鐵礦的作用過(guò)程和機(jī)理,。該研究對(duì)揭示土壤的本質(zhì)，合理調(diào)節(jié)土壤生物活性,，闡明細(xì)菌黏附,、生物膜形成和功能機(jī)制以及污染物的遷移分布等具有重要的理論和實(shí)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(jī)物復(fù)合體表面，形成單個(gè)的微菌落或生物膜,。在形成生物膜之前,，細(xì)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(xì)菌的黏附和遷移,，進(jìn)而影響生物膜的結(jié)構(gòu)和功能,。
方臨川研究發(fā)現(xiàn)，細(xì)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(tuán)與針鐵礦表面羥基配位形成內(nèi)圈絡(luò)合物,，且吸附產(chǎn)物結(jié)構(gòu)與體系pH有密切關(guān)聯(lián)。低pH時(shí)（pH為3.0）,，磷酸基團(tuán)僅有一個(gè)去質(zhì)子化的含氧陰離子直接和針鐵礦表面的FeOH1/2-基團(tuán)結(jié)合形成單齒絡(luò)合物,；而在高pH時(shí)（pH為9.0），磷酸鹽基團(tuán)中有2個(gè)含氧陰離子和針鐵礦表面的2個(gè)FeOH1/2-基團(tuán)結(jié)合形成雙齒絡(luò)合物,。同時(shí),，體系pH由低到高時(shí)（3.0～9.0），吸附產(chǎn)物構(gòu)型由單基配位向雙基配位過(guò)渡,，從而揭示出體系pH通過(guò)影響溶液中EPS-P中磷酸根質(zhì)子解離和締合,，為導(dǎo)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(guò)程中可能存在某種分子識(shí)別機(jī)制,，細(xì)菌分泌的胞外聚合物與針鐵礦之間P-O-Fe鍵的形成對(duì)于細(xì)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.
