Soil organic matter and the extracellular microbial matrix show contrasting responses to C and N availability.
Soil organic matter and the extracellular microbial matrix show contrasting responses to C and N availability.
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DOI：
10.1016/j.soilbio.2015.05.025
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发表时间：
2015-09
影响因子：
9.7
通讯作者：
Goulding KW
中科院分区：
文献类型：
--
作者：
Redmile-Gordon MA;Evershed RP;Hirsch PR;White RP;Goulding KW
土壤科学中的一个新兴范式表明，微生物可以在氮利用率低的条件下从顽固的土壤有机质（SOM）中进行“氮挖掘”。然而，这需要产生富含氮的细胞外结构（包括酶和结构成分），因此违背了化学计量预期。我们着手从土壤细胞外基质中提取新合成的肽，并比较氨基酸 (AA) 谱、氮掺入和 AA 动力学，以响应对比 C/N 比的不稳定输入。将含有或不含无机氮源（10% 15N 标记的 NH4NO3）的甘油添加到已经含有大量难熔 SOM 的土壤中，并培养 10 天。使用比色法、气相色谱法和同位素比质谱法对所得总土壤肽 (TSP) 和细胞外池进行比较。 N同位素组成表明，细胞外聚合物（EPS）比TSP含有更大比例的从头形成的产物，疏水性EPS-AA（亮氨酸、异亮氨酸、苯丙氨酸、羟脯氨酸和酪氨酸）从所提供的无机源中衍生出更多的N。提取物之间的定量比较表明，EPS 含有相对比例较高的丙氨酸、甘氨酸、脯氨酸、苯丙氨酸和酪氨酸。 EPS 肽和 EPS 多糖浓度的最大增加发生在 C/N 比最高时。所有 EPS-AA 对治疗的反应相似，而 TSP 的反应则更为复杂。结果表明，细胞外氮（如 EPS 肽）的投入是低氮/高碳条件下微生物的生存机制，从进化的角度来看，这最终必然导致微生物生物量的氮回报增加的趋势。提出了一个概念模型，描述细胞外基质响应不稳定输入的 C/N 比的动态。细胞外聚合物 (EPS) 随不稳定的 C 可用性而增加。 EPS 生产效率随可用基质的 C/N 比降低。提出了 EPS 对输入 C/N 比响应的概念模型。高e-多糖与改进的细胞外肽提取相结合。蛋白质的比色分析反映了 GC/FID 给出的类似趋势。
An emerging paradigm in soil science suggests microbes can perform ‘N mining’ from recalcitrant soil organic matter (SOM) in conditions of low N availability. However, this requires the production of extracellular structures rich in N (including enzymes and structural components) and thus defies stoichiometric expectation. We set out to extract newly synthesised peptides from the extracellular matrix in soil and compare the amino acid (AA) profiles, N incorporation and AA dynamics in response to labile inputs of contrasting C/N ratio. Glycerol was added both with and without an inorganic source of N (10% 15N labelled NH4NO3) to a soil already containing a large pool of refractory SOM and incubated for 10 days. The resulting total soil peptide (TSP) and extracellular pools were compared using colorimetric methods, gas chromatography, and isotope ratio mass spectrometry. N isotope compositions showed that the extracellular polymeric substance (EPS) contained a greater proportion of products formed de novo than did TSP, with hydrophobic EPS-AAs (leucine, isoleucine, phenylalanine, hydroxyproline and tyrosine) deriving substantially more N from the inorganic source provided. Quantitative comparison between extracts showed that the EPS contained greater relative proportions of alanine, glycine, proline, phenylalanine and tyrosine. The greatest increases in EPS-peptide and EPS-polysaccharide concentrations occurred at the highest C/N ratios. All EPS-AAs responded similarly to treatment whereas the responses of TSP were more complex. The results suggest that extracellular investment of N (as EPS peptides) is a microbial survival mechanism in conditions of low N/high C which, from an evolutionary perspective, must ultimately lead to the tendency for increased N returns to the microbial biomass. A conceptual model is proposed that describes the dynamics of the extracellular matrix in response to the C/N ratio of labile inputs. Extracellular polymeric substances (EPS) increased with labile C availability. EPS production efficiency decreased with C/N ratio of available substrate. A conceptual model for the EPS response to C/N ratio of inputs is proposed. High e-polysaccharide was coupled with improved extracellular peptide extraction. Colorimetric analysis of protein reflected similar trends given by GC/FID.