PDF(Pubmed)
Abstract：
The central carbon (C) metabolic network is responsible for most of the production of energy and biosynthesis in microorganisms and is therefore key to a mechanistic understanding of microbial life in soil communities. Many upland soil communities have shown a relatively high C flux through the pentose phosphate (PP) or the Entner-Doudoroff (ED) pathway, thought to be related to oxidative damage control. We tested the hypothesis that the metabolic organization of the central C metabolic network differed between two ecosystems, an anoxic marsh soil and oxic upland soil, and would be affected by altering oxygen concentrations. We expected there to be high PP/ED pathway activity under high oxygen concentrations and in oxic soils and low PP/ED activity in reduced oxygen concentrations and in marsh soil. Although we found high PP/ED activity in the upland soil and low activity in the marsh soil, lowering the oxygen concentration for the upland soil did not reduce the relative PP/ED pathway activity as hypothesized, nor did increasing the oxygen concentration in the marsh soil increase the PP/ED pathway activity. We speculate that the high PP/ED activity in the upland soil, even when exposed to low oxygen concentrations, was related to a high demand for NADPH for biosynthesis, thus reflecting higher microbial growth rates in C-rich soils than in C-poor sediments. Further studies are needed to explain the observed metabolic diversity among soil ecosystems and determine whether it is related to microbial growth rates.IMPORTANCEWe observed that the organization of the central carbon (C) metabolic processes differed between oxic and anoxic soil. However, we also found that the pentose phosphate pathway/Entner-Doudoroff (PP/ED) pathway activity remained high after reducing the oxygen concentration for the upland soil and did not increase in response to an increase in oxygen concentration in the marsh soil. These observations contradicted the hypothesis that oxidative stress is a main driver for high PP/ED activity in soil communities. We suggest that the high PP/ED activity and NADPH production reflect higher anabolic activities and growth rates in the upland soil compared to the anaerobic marsh soil. A greater understanding of the molecular and biochemical processes in soil communities is needed to develop a mechanistic perspective on microbial activities and their relationship to soil C and nutrient cycling. Such an increased mechanistic perspective is ecologically relevant, given that the central carbon metabolic network is intimately tied to the energy metabolism of microbes, the efficiency of new microbial biomass production, and soil organic matter formation.
摘要：
中心碳（C）代谢网络负责微生物中大部分能量的产生和生物合成，因此是对土壤群落中微生物生命的机械理解的关键。许多旱地土壤群落通过磷酸戊糖（PP）或Entner-Doudoroff（ED）途径显示出相对较高的C通量，认为与氧化损伤控制有关。我们检验了这样一个假设，即中央C代谢网络的代谢组织在两个生态系统之间是不同的，缺氧沼泽土壤和多氧旱地土壤，并且会受到氧气浓度变化的影响。我们预计，在高氧浓度和高氧土壤中，PP/ED途径活性较高，而在降低的氧浓度和沼泽土壤中，PP/ED活性较低。尽管我们在旱地土壤中发现了较高的PP/ED活性，而在沼泽土壤中发现了较低的活性。降低旱地土壤的氧浓度并没有降低假设的相对PP/ED途径活性，增加沼泽土壤中的氧气浓度也没有增加PP/ED途径的活性。我们推测旱地土壤中的高PP/ED活性，即使暴露在低氧浓度下，与生物合成对NADPH的高需求有关，因此反映了富碳土壤中的微生物生长速率高于贫碳沉积物。需要进一步的研究来解释土壤生态系统中观察到的代谢多样性，并确定它是否与微生物生长速率有关。重要性我们观察到，高氧和缺氧土壤之间的中心碳（C）代谢过程的组织不同。然而,我们还发现，戊糖磷酸途径/Entner-Doudoroff（PP/ED）途径活性在降低旱地土壤的氧气浓度后仍然很高，并且不会响应沼泽土壤中氧气浓度的增加而增加。这些观察结果与以下假设相矛盾：氧化应激是土壤群落中高PP/ED活性的主要驱动因素。我们建议，与厌氧沼泽土壤相比，高PP/ED活性和NADPH产量反映了旱地土壤中更高的合成代谢活性和生长速率。需要对土壤群落中的分子和生化过程有更深入的了解，以发展对微生物活动及其与土壤碳和养分循环的关系的机理观点。这种增加的机械观点在生态上是相关的，考虑到中心碳代谢网络与微生物的能量代谢密切相关，新微生物生物质生产的效率，和土壤有机质的形成。
