Tabares Marcela, Kashefi Kazem, Reguera Gemma
Department of Microbiology, Genetics & Immunology, Michigan State University, East Lansing, MI 48824, United States.
ISME J. 2025 Jan 2;19(1). doi: 10.1093/ismejo/wraf054.
Poorly understood microorganisms "short-circuit" the nitrogen cycle via the dissimilatory nitrate reduction to ammonium to retain the element in agricultural lands and stimulate crop productivity. The prevalence of Geobacterales closely related to Trichlorobacter lovleyi in nitrate ammonification hotspots motivated us to investigate adaptive responses contributing to ammonification rates in the laboratory type strain T. lovleyi SZ. Here, we describe the identification of tightly regulated pathways for efficient nitrate foraging and respiration with acetate, an important intermediate of organic matter degradation that Geobacterales efficiently assimilate and oxidize. Challenging the established dogma that high carbon/nitrate ratios stimulate the reduction of nitrate to ammonium, T. lovleyi doubled rapidly across a wide range of ratios provided nitrate concentrations were low enough to prevent the accumulation of the toxic nitrite intermediate. Yet, excess electrons during hydrogenotrophic growth alleviated nitrite toxicity and stimulated the reduction of nitrate to ammonium even under conditions of severe acetate limitation. These findings underscore the importance of nitrite toxicity in the ammonification of nitrate by Geobacterales and provide much needed mechanistic understanding of microbial adaptations contributing to soil nitrogen conservation. This information is critical to enhance the predictive value of genomic-based traits in environmental surveys and to guide strategies for sustainable management of nitrogen fertilization as well as mitigation of green-house emissions and agrochemical leaching from agricultural lands.
了解甚少的微生物通过异化硝酸盐还原为铵的过程使氮循环“短路”，从而将该元素保留在农田中并提高作物生产力。在硝酸盐氨化热点地区，与可爱三氯杆菌密切相关的地杆菌目细菌的普遍存在促使我们研究实验室模式菌株可爱三氯杆菌SZ中有助于氨化速率的适应性反应。在这里，我们描述了高效硝酸盐觅食以及利用醋酸盐进行呼吸作用的严格调控途径的鉴定，醋酸盐是地杆菌目细菌有效同化和氧化的有机物降解的重要中间体。挑战了高碳/硝酸盐比率会刺激硝酸盐还原为铵的既定观念，只要硝酸盐浓度足够低以防止有毒亚硝酸盐中间体的积累，可爱三氯杆菌在很宽的比率范围内都能迅速翻倍。然而，在氢营养型生长过程中过量的电子减轻了亚硝酸盐毒性，甚至在严重醋酸盐限制的条件下也刺激了硝酸盐还原为铵。这些发现强调了亚硝酸盐毒性在地杆菌目细菌硝酸盐氨化中的重要性，并为有助于土壤氮素保持的微生物适应性提供了急需的机制理解。这些信息对于提高环境调查中基于基因组特征的预测价值以及指导氮肥可持续管理策略以及减轻农田温室气体排放和农用化学品淋溶至关重要。
