Investigating host-induced lipopolysaccharide changes in the legume symbiont Sinorhizobium meliloti

细菌对生命有有益的影响，也有消极的影响。例如，土壤细菌紫花苜蓿和豆科植物之间的相互作用是有益的，因为这种细菌将大气中的氮转化为植物可以利用的形式。作为回报，细菌从植物中获得营养。结果是细菌在植物体内长期生存并促进植物生长的共生关系。我对了解使细菌能够在植物细胞内长期生存的因素很感兴趣。这一点很重要，因为豆科植物是主要的食物来源，而且由于细菌产生的氮源最终被释放到土壤中，这一过程减少了向土壤中添加昂贵的氮肥的需要。了解流程是如何工作的，是改进流程的第一步。有趣的是，土壤细菌与另一种细菌--流产布鲁氏菌有关，后者会导致牛流产，并导致人类感染一种被称为布鲁氏菌病的严重感染。人们对布鲁氏菌致病的重要因素知之甚少，但就像植物细胞内的土壤细菌一样，布鲁氏菌可以在动物和人类细胞内长期存活。牛可以接种疫苗来预防布鲁氏菌感染，但使用的疫苗在很大程度上没有特点。不幸的是，目前还没有针对布鲁氏菌的人类疫苗，鉴于布鲁氏菌是潜在的生物恐怖分子，这是一个问题。因此，更多地了解布鲁氏菌感染可能有助于开发人类疫苗，并改进现有的牛疫苗。最近的证据表明，土壤细菌和布鲁氏菌分别在植物和动物/人类细胞内长期生存的策略有共同点。我的研究表明，细菌细胞外部的脂多糖(LPS)结构对长期生存非常重要。以土壤细菌-植物相互作用为模型系统，研究了细菌与植物相互作用过程中细菌内毒素的变化。因此，这项建议的总体目标是描述这些植物诱导的内毒素变化的特征，确定细菌细胞如何导致这些内毒素变化，并确定这些内毒素变化是否与土壤细菌在植物中的长期生存有关。这些研究的结果不仅可以提高我们对共生的认识，还可以为细菌如何在动物和人类细胞中长期生存提供见解。

Bacteria can have both beneficial and negative impacts upon life. For example, the interaction between the soil bacterium, Sinorhizobium meliloti, and leguminous plants is beneficial since the bacteria convert nitrogen from the atmosphere into a form which can be utilised by plants. In return, the bacteria obtain nutrients from the plant. The outcome is a symbiosis where the bacteria survive long-term within the plant and promote plant growth. I am interested in understanding the factors, which enable the bacteria to survive long-term within plant cells. This is important since leguminous plants are major food sources and, since the nitrogen source produced by the bacteria is eventually released into the soil, this process alleviates the need to add costly nitrogen fertilisers to the soil. Understanding how processes work, is the first step towards improving processes. Interestingly, the soil bacterium is related to another bacterium, Brucella abortus, which causes abortions in cattle and results in a severe infection in humans known as Brucellosis. The factors important for Brucella to cause disease are poorly understood, but like the soil bacteria within plant cells, Brucella can survive long-term within animal and human cells. Cattle can be vaccinated to prevent Brucella infection, but the vaccine used is largely uncharacterised. Unfortunately, there is no human vaccine against Brucella and this is a problem given that Brucella are potential bioterrorism agents. Thus, understanding more about Brucella infections could help in the development of a human vaccine and improve the exisiting cattle vaccine. Recent evidence suggest that there are commonalities in the strategies used by the soil bacterium and Brucella to survive long-term within plant and animal/human cells, respectively. My research suggests that structures on the outside of the bacterial cell known as lipopolysaccharides (LPS) are important for long-term survival. By using the soil bacterium-plant interaction as a model system, I identified that the bacterial LPS changes during the interaction with the plant. Thus, the overall goal of this proposal is to characterise these plant-induced LPS changes, to determine how the bacterial cell brings about these LPS changes and to determine whether these LPS changes are involved in the long-term surival of the soil bacterium within plant. The outcome of these studies could not only improve our knowledge of the symbiosis but could also provide insights into how bacteria can surive long-term within animal and human cells.