The Ecological Significance of Molecular Signaling Between Bacterial Populations on Plant Roots: Effect on Competitionand Coexistence

9514074皮尔逊根际，即植物根部周围的土壤地带，含有比周围土壤更多的以根分泌物形式存在的营养物质。因此，这些根分泌物的微生物竞争是激烈的。为了应对这种竞争，细菌进化出了不同的竞争机制，使它们能够竞争这些营养物质。表达这些竞争机制的一个好处是抑制植物病原体，通常称为生物防治。然而，生物防治的商业应用受到性能不一致的限制。这是由于我们缺乏对影响这些竞争基因在根际表达的因素的了解，包括植物寄主和自然微生物群落。金黄色假单胞菌30-84是最好的遗传生物控制生物之一，能产生吩嗪类抗生素。吩嗪的产生是该物种在根际的竞争适合度和抑制植物病原体能力的主要机制。我们已经证明，这种细菌通过识别由基因phzI编码的扩散信号来调节编码吩嗪生产的基因的表达。最近，有研究表明，不同的细菌种群依赖于结构相似的信号的积累来触发宿主相关基因的表达。我们已经证明，菌株30-84中参与吩嗪产生的基因的表达受到其他根际细菌产生的扩散信号的影响。这些相互作用的生态学意义在于，竞争菌株可能能够通过在基因水平上影响竞争机制的调节来影响竞争的结果。这项拟议的研究将直接测试其他细菌种群产生的扩散信号对金黄色葡萄球菌吩嗪基因表达的影响，包括相互作用对植物根部种群密度的影响。

9514074 Pierson The rhizosphere, the zone of soil surrounding plant roots, contains greater amounts of nutrients in the form of root exudate than the surrounding soil. Therefore, microbial competition for these root exudates is intense. In response to this competition, bacteria have evolved diverse competitive mechanisms to allow them to compete for these nutrients. One benefit of the expression of these competitive mechanisms is the inhibition of plant pathogens, commonly termed biological control. However, commercial use of biological control as been limited by inconsistent performance. This is the result of our lack of understanding of the factors, including the plant host and the natural microbial community, that affect the expression of these competitive genes in the rhizosphere. Pseudomonas aureofaciens 30-84, one of the best genetically defined biological control organisms, produces phenazine antibiotics. Phenazine production is the primary mechanism responsible for the competitive fitness of this species in the rhizosphere and for its ability to suppress plant pathogens. We have shown that this bacterium regulates the expression of the genes encoding phenazine production through the recognition of a diffusible signal encoded by the gene phzI. Recently, it has been shown that populations of diverse bacteria rely on the accumulation of structurally similar signals to trigger the expression of host-associated genes. We have shown that the expression of genes involved in phenazine production in strain 30-84 is influenced by the production of diffusible signals produced by other rhizosphere bacteria. The ecological significance of these interactions is that competing strains may be able to influence the outcome of competition by affecting the regulation of a competitive mechanism at a genetic level. The proposed research will directly test the effect of diffusible signals produced by other populations of bacteria on phenazine gene expression in P. aureofaciens, including the effect of interactions on population densities in situ on plant roots.