Although nitrogen fertilizers have certain benefits, the over application of such compounds often results in damages to the ecosystem. In this project, we focus our study on Sinorhizobiom meliloti, a species that lives in symbiosis with alfalfa plants, and through its nitrogen fixation capabilities, restores nitrogen levels in the soil. In our study we aim to gain a better understanding of the carbon metabolism in S. meliloti, mainly by looking at growth patterns in the presence of different carbon sources. Our research picked up on Erik Arvey’s discoveries which pointed out that sucrose inhibits growth of certain glucose minus mutants of S. meliloti on a lactate and aspartate medium. Due to this rather odd mutant behavior, we began our experimentation by growing mutant strains on other similar disaccharides such as cellobiose and trehalose, the breakdown products of sucrose, fructose and glucose, and increasing fructose concentrations. We even generated new mutant strains via TN5 mutagenesis to investigate their behavior as well. Overall we found out that other disaccharides don’t inhibit growth and fructose which caused the highest degree of inhibition managed to slow down the growth over a longer period of time. Sucrose, also appeared to inhibit growth on succinate and aspartate medium, and nitrogen and lactate medium, suggesting that this growth delayed in the mutants could be due to a metabolite accumulating in the cell, or that the cells waste energy in breaking down sucrose which cannot be further metabolized. We also grew S. meliloti mutant and wildtype strains on gluconolactone, which helped us pin-point our library of mutations in the Entner-Doudoroff pathway.
Apostol, R. (2017). Investigation of Media Effects on Sinorhizobium meliloti Glucose Minus (Undergraduate honors thesis, University of Redlands). Retrieved from http://inspire.redlands.edu/cas_honors/159