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

根际，即植物根系周围的土壤区域，以根系渗出物的形式比周围的土壤含有更多的养分。因此，微生物对这些根分泌物的竞争是激烈的。为了应对这种竞争，细菌进化出了多种竞争机制，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，通常称为生物控制。然而，生物防治的商业应用由于效果不一致而受到限制。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理解，包括植物宿主和天然微生物群落。金黄色假单胞菌（Pseudomonas aureofaciens） 30-84是一种具有良好遗传定义的生物防治生物，可生产非那嗪类抗生素。非那嗪的产生是该物种在根际竞争适应性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phzI基因编码的扩散信号来调节编码非那嗪生产的基因的表达。最近，研究表明，不同细菌群体依赖于结构相似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中参与苯那嗪生产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意义在于，竞争菌株可能能够通过在遗传水平上影响竞争机制的调节来影响竞争的结果。本研究将直接测试其他细菌群体产生的扩散信号对金黄色葡萄球菌中吩那嗪基因表达的影响，包括相互作用对植物根系原位种群密度的影响。

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.