Characterization of the Sinorhizobum Meliloti Chotaxis System

Increasing awareness to global climate change has drastically focused attention on finding solutions to reduce environmental impacts while still providing sufficient food for the increasing world population. Beneficial Nitrogen Fixing (BNF) microbes provide a possible solution by delivering biological nitrogen to plants resulting in reduced environmental impacts due to fertilizer runoff and eutrophication. One well studied model is that of Sinorhizobium meliloti and its legume host Medicago sativa (alfalfa), the fourth largest USA crop used for animal feed. Advancing research for this symbiosis model can provide solutions to enhance yield while minimizing environmental impacts.

Chapter 2 focuses on the deviation of the S. meliloti chemotaxis system from the enteric paradigm. Quantitative immunoblots determined the cellular amounts of chemotaxis proteins. Overall, chemotaxis protein levels were approximately 10-fold lower in S. meliloti compared to B. subtilis and E. coli. Focusing on cellular stoichiometric ratios, S. meliloti generally exhibits drastically higher values for CheB, CheR, and CheY to the histidine kinase CheA monomer compared to E. coli and B. subtilis.

Chapter 3 characterizes the role of McpX to quaternary ammonium compound (QAC) sensing. QACs are exuded by germinating alfalfa seeds. In vitro binding assays were performed to determine ligand binding characteristics. S. meliloti chemotaxis behavior to QACs was analyzed in in vivo capillary assays under real-time imaging.

These studies strengthen our knowledge of the chemotaxis system in the symbiosis model of S. meliloti and alfalfa. The data can further be used to create a mathematical model of the dynamics of bacteria-host interaction. The results can be used to optimize chemotaxis to host plants to improve crop yield and protect watersheds.