Soil microbial communities host a large number of microbial species that support important ecological functions such as biogeochemical cycling and plant nutrition. The extent and stability of these functions are affected by inter-species interactions among soil microorganisms, yet the different mechanisms underpinning microbial interactions in the soil are not fully understood. Here, we study the extent of nutrient-based interactions among two model, plant-supporting soil microorganisms, the fungi Serendipita indica, and the bacteria Bacillus subtilis. We found that S. indica is unable to grow with nitrate - a common nitrogen source in the soil - but this inability could be rescued, and growth restored in the presence of B. subtilis. We demonstrate that this effect is due to B. subtilis utilising nitrate and releasing ammonia, which can be used by S. indica. We refer to this type of mechanism as ammonia mediated nitrogen sharing (N-sharing). Using a mathematical model, we demonstrated that the pH dependent equilibrium between ammonia (NH3) and ammonium (NH+4) results in an inherent cellular leakiness, and that reduced amonnium uptake or assimilation rates could result in higher levels of leaked ammonia. In line with this model, a mutant B. subtilis – devoid of ammonia uptake - showed higher S. indica growth support in nitrate media. These findings highlight that ammonia based N-sharing can be a previously under-appreciated mechanism underpinning interaction among soil microorganisms and could be influenced by microbial or abiotic alteration of pH in microenvironments.

中文翻译：

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氨泄漏可以支持土壤微生物之间的氮共享


土壤微生物群落拥有大量微生物物种，支持生物地球化学循环和植物营养等重要生态功能。这些功能的程度和稳定性受到土壤微生物之间物种间相互作用的影响，但土壤中微生物相互作用的不同机制尚未完全了解。在这里，我们研究了两种模型（植物支持土壤微生物、真菌 Serendipita indica 和细菌枯草芽孢杆菌）之间基于营养的相互作用的程度。我们发现，S. indica 无法在硝酸盐（土壤中常见的氮源）下生长，但这种能力可以被挽救，并且在枯草芽孢杆菌存在的情况下恢复生长。我们证明这种效应是由于枯草芽孢杆菌利用硝酸盐并释放氨而引起的，而这些氨可以被印度链球菌利用。我们将这种类型的机制称为氨介导的氮共享（N-sharing）。使用数学模型，我们证明氨 (NH3) 和铵 (NH+4) 之间的 pH 依赖性平衡会导致固有的细胞泄漏，并且铵吸收或同化率的降低可能会导致氨泄漏水平更高。与该模型一致，缺乏氨吸收的枯草芽孢杆菌突变体在硝酸盐培养基中显示出更高的印度链球菌生长支持。这些发现强调，基于氨的氮共享可能是一种先前未被充分认识的支撑土壤微生物之间相互作用的机制，并且可能受到微环境中微生物或非生物 pH 值改变的影响。