Environmental Determinants of Microbial Biopolymer Degraders in Agricultural Soil

植物、真菌和节肢动物的结构多糖纤维素和几丁质是农业土壤中有机质的主要成分。这些生物聚合物是与土壤氧化还原过程相关的土壤微生物群落的碳源。水不饱和土壤团聚体形成了外部好氧条件和内部限氧条件的自然边界。这些地球化学界面导致在毫米尺度上高度不均匀的氧分布。除草剂对这种高度区隔化土壤中生物聚合物降解群落的毒性效应和机制尚未得到解决。该研究是优先计划1315“土壤中的生物地球化学界面”资助项目的延续。前一个项目解决了已知的和新的原核生物的系统发育身份与纤维素降解在好氧和缺氧条件下，并证明了酸性除草剂苯达松和MCPA损害纤维素降解涉及的微生物过程。拟议的项目将（I）确定几丁质降解原核生物，真菌和原生生物是活跃在好氧和缺氧微区，（II）确定各种纤维素分解和几丁质分解类群苯达松和MCPA的耐受性，（III）表征关键几丁质降解剂，（IV）将定量评估农业土壤中生物聚合物降解过程中的氧分布。主要方法包括稳定同位素探测、16S rRNA、18S rRNA和几丁质酶基因分析、HPLC、GC和通过荧光染料分析的氧传感。

The structural polysaccharides cellulose and chitin of plants, fungi, and arthropods are major components of organic matter in agricultural soils. These biopolymers are carbon sources of soil microbial communities linked to soil redox processes. Soil aggregates of waterunsaturated soil form natural boundaries of oxic conditions outside and oxygen-limited conditions inside. These biogeochemical interfaces lead to a highly heterogeneous oxygen distribution on a millimetre scale. The effects and mechanisms of the toxicity of herbicides on biopolymer degrading communities in such highly compartmentalized soils have not been resolved. The proposed study is a continuation of a project funded within Priority Program 1315 ‘Biogeochemical Interfaces in Soil’. The preceding project resolved phylogenetic identities of known and novel prokaryotes linked to cellulose degradation under both oxic and anoxic conditions, and demonstrated that the acidic herbicides Bentazon and MCPA impair microbial processes involved in cellulose degradation. The proposed project will (I) identify chitin-degrading prokaryotes, fungi, and protists that are active in oxic and anoxic microzones, (II) determine the tolerance of various cellulolytic and chitinolytic taxa to Bentazon and MCPA, (III) characterize key chitin-degraders, and (IV) will quantitatively assess oxygen distribution in during biopolymer degradation in an agricultural soil. Central methods will include stable isotope probing, analyses of 16S rRNA, 18S rRNA, and chitinase genes, HPLC, GC, and oxygen sensing via analysis of fluorescence dyes.