Peptidoglycan remodelling during Rhizobium leguminosarum life cycle, from the rhizosphere to the formation of bacteroids

植物的最佳生长是通过与土壤微生物包括细菌、真菌、单细胞动物和线虫的复杂相互作用来实现的。属于蚕豆科(豆科)的植物(如豌豆、豆类、大豆或小扁豆)依靠与一组称为根瘤菌的细菌进行互利的相互作用(共生)来利用大气中的氮。这种基本营养物质以一种气体的形式存在，占地球大气的78%，但不能直接被植物用来合成它们的细胞成分。因此，根瘤菌对氮素的吸收是植物生长的关键过程，而植物生长反过来又支持动物的生命，从而产生巨大的经济和环境影响。人工氮肥的使用具有重大的环境成本；它占农业使用的化石燃料的近50%，并导致湖泊、河流和饮用水的富营养化，有毒藻类大量繁殖，以及生物多样性的丧失。植物-根瘤菌共生涉及一个复杂的分子对话，导致细菌入侵根组织，形成根瘤。在这些根瘤内，根瘤菌形成了被称为类杆菌的特殊细胞，能够将大气中的氮转化为植物使用的氨。我们已经确定了一系列在模式共生菌豆类根瘤的生命周期中差异表达的酶，它们对根瘤中细菌的生存是必不可少的。这项研究的目的是研究这组重要的蛋白质，以了解细菌细胞膜的重塑如何有助于豌豆和豆类的共生。这项工作是为可持续农业培育根瘤菌的重要一步。

Optimal plant growth is achieved through complex interactions with soil microorganisms including bacteria, fungi, single celled animals, and nematodes. Plants belonging to the family of Fabaceae (legumes such as peas, beans, soybeans, or lentils) rely on a mutually beneficial interaction (symbiosis) with a group of bacteria called rhizobia to utilise atmospheric nitrogen. This basic nutrient is present as a gas that makes up 78% of Earth's atmosphere but cannot be used directly by plants for the synthesis of their cellular constituents. Assimilation of nitrogen by rhizobia is therefore a critical process for plant growth, which in turn supports animal life, with a tremendous economic and environmental impact. The use of artificial nitrogen fertilisers has a major environmental cost; it accounts for nearly 50% of the fossil fuel used in agriculture and leads to eutrophication of lakes, rivers and drinking water, toxic algal blooms, and biodiversity loss. The plant-rhizobia symbiosis involves a complex molecular dialog that leads to the bacterial invasion of root tissues and the formation of root nodules. Inside these nodules, rhizobia form specialised cells called bacteroids able to transform atmospheric nitrogen into ammonia used by plants. We have identified a family of enzymes that are differentially expressed during the life cycle of the model symbiont Rhizobium leguminosarum and essential for the viability of bacteria in the nodule. The purpose of this research is to study this group of important proteins to understand how the remodelling of the bacterial cell envelope contributes to symbiosis in peas and beans. This work is an important step to engineer rhizobia for sustainable agriculture.