Laboratorio de Ecología Microbiana y Microbiología Ambiental, Departamento de Biociencias, Facultad de Química, Universidad de la República, Montevideo, Uruguay.
Graduate Program in Chemistry, Facultad de Química, Universidad de la República, Montevideo, Uruguay.
Appl Environ Microbiol. 2024 Apr 17;90(4):e0235123. doi: 10.1128/aem.02351-23. Epub 2024 Mar 22.
In rice paddies, soil and plant-derived organic matter are degraded anaerobically to methane (CH), a powerful greenhouse gas. The highest rate of methane emission occurs during the reproductive stage of the plant when mostly dicarboxylic acids are exudated by the roots. The emission of methane at this stage depends largely on the cooperative interaction between dicarboxylic acid-fermenting bacteria and methanogenic archaea in the rhizosphere. The fermentation of tartrate, one of the major acids exudated, has been scarcely explored in rice paddy soils. In this work, we characterized an anaerobic consortium from rice paddy soil composed of four bacterial strains, whose principal member (LT8) can ferment tartrate, producing H and acetate. Tartrate fermentation was accelerated by co-inoculation with a hydrogenotrophic methanogen. The assembled genome of LT8 possesses a Na-dependent oxaloacetate decarboxylase and shows that this bacterium likely invests part of the H produced to reduce NAD(P) to assimilate C from tartrate. The phylogenetic analysis of the 16S rRNA gene, the genome-based classification as well as the average amino acid identity (AAI) indicated that LT8 belongs to a new genus within the family. LT8 shares a few common features with its closest relatives, for which tartrate degradation has not been described. LT8 is limited to a few environments but is more common in rice paddy soils, where it might contribute to methane emissions from root exudates.IMPORTANCEThis is the first report of the metabolic characterization of a new anaerobic bacterium able to degrade tartrate, a compound frequently associated with plants, but rare as a microbial metabolite. Tartrate fermentation by this bacterium can be coupled to methanogenesis in the rice rhizosphere where tartrate is mainly produced at the reproductive stage of the plant, when the maximum methane rate emission occurs. The interaction between secondary fermentative bacteria, such as LT8, and methanogens could represent a fundamental step in exploring mitigation strategies for methane emissions from rice fields. Possible strategies could include controlling the activity of these secondary fermentative bacteria or selecting plants whose exudates are more difficult to ferment.
在稻田中，土壤和植物源有机质在厌氧条件下降解为甲烷（CH），这是一种强大的温室气体。甲烷排放的最高速率发生在植物的生殖阶段，此时根系主要分泌二羧酸。在这个阶段，甲烷的排放在很大程度上取决于根际中二羧酸发酵细菌和产甲烷古菌之间的协同相互作用。在水稻土中，对主要分泌酸之一酒石酸的发酵作用研究甚少。在这项工作中，我们从稻田土壤中分离出了一个厌氧菌群，该菌群由 4 株细菌组成，其主要成员（LT8）可以发酵酒石酸，产生 H 和乙酸。共接种氢营养型产甲烷菌可以加速酒石酸发酵。LT8 的组装基因组含有一个 Na 依赖性草酰乙酸脱羧酶，并表明该细菌可能将部分 H 用于还原 NAD(P)，以从酒石酸中同化 C。16S rRNA 基因的系统发育分析、基于基因组的分类以及平均氨基酸同一性（AAI）表明，LT8 属于 科的一个新属。LT8 与最接近的亲缘关系有一些共同特征，但尚未描述其酒石酸降解能力。LT8 仅局限于少数环境中，但在稻田土壤中更为常见，在那里它可能有助于根系分泌物的甲烷排放。
重要性这是第一个报告代谢特征的新的厌氧细菌能够降解酒石酸，一种经常与植物相关联的化合物，但作为微生物代谢物很少见。这种细菌的酒石酸发酵可以与水稻根际中的产甲烷作用相偶联，在植物的生殖阶段，即甲烷排放的最高速率发生时，主要产生酒石酸。次级发酵细菌（如 LT8）与产甲烷菌之间的相互作用可能是探索从稻田中减少甲烷排放的缓解策略的一个基本步骤。可能的策略包括控制这些次级发酵细菌的活性或选择其分泌物更难发酵的植物。
