The Drilosphere as a Driver of Microbial Metabolism of Herbicides in Soil: Linking Processes with Populations

除草剂在农业中被广泛使用。苯氧烷酸（PAA）除草剂及其衍生物的降解在钻井圈（即蚯蚓肠道内容物、粪便和地穴）中被催化。洞壁代表了土壤中高达1.2 m2 m-3的界面，是PAA除草剂有氧降解的“热点”。蚯蚓的生态类型（即附生种、内生种或内源种）可能影响地穴形成的强度，从而影响除草剂的降解。然而，蚯蚓生态类型对除草剂降解的影响尚不清楚。许多除草剂的降解途径，相关的结构基因和相关的生物在钻井圈，是很差的解决。基于这些信息的不足，将对以下假设进行检验：(i)钻探圈蕴藏着迄今为止未知的、转化除草剂苯达松的高活性原核生物；（ii）蚯蚓对PAA、2,4-二氯酚和苯达松降解的生态型影响。降解中间体和产物将由高效液相色谱和闪烁计数测定。减法转录组分析和454焦磷酸测序将确定参与除草剂降解的结构基因。16S rRNA稳定同位素探测、定量结构基因靶向PCR、最可能数分析和分离方法将用于鉴定和表征过程相关的微生物种群。

Herbicides are widely used in agriculture. Degradation of phenoxyalkanoic acid (PAA) herbicides and their derivatives is catalyzed in the drilosphere (i.e., earthworm gut content, cast, and burrows). Burrow walls represent interfaces in soil with up to 1.2 m2 m-3 and are ‘hotspots’ for the aerobic degradation of PAA herbicides. Earthworm eco-types (i.e., epigeic, anecic, or endogeic species) might impact on the intensity of burrow formation and thus herbicide degradation. However, the effect of earthworm eco-type on herbicide degradation is unknown. Degradation pathways of many herbicides, associated structural genes, and associated organisms in the drilosphere, are poorly resolved. Based on these deficiencies of information, the following hypotheses will be tested: (i) the drilosphere harbors hitherto unknown, highly active prokaryotes that transform the herbicide bentazon and (ii) the earthworm eco-type impacts on PAA, 2,4-dichlorophenol, and bentazon degradation. Degradation intermediates and products will be determined by high performance liquid chromatography and scintillation counting. Subtractive transcriptome analysis and 454 pyrosequencing will identify structural genes involved in herbicide degradation. 16S rRNA stable isotope probing, quantitative structural gene-targeted PCR, most probable number analyses, and isolation approaches will be utilized to identify and characterize process-associated microbial populations.