Hamline News

April 27, 2012

Analyzing Expression of 1-Aminocyclopropane-1-Carboxylate (ACC) Deaminase in Strains of Sinorhizobium

Alyssa Renn, Advisor: Betsy Martinez-Vaz

Nitrogen-fixing bacteria like Sinorhiziobia have the ability to convert nitrogen gas into ammonia, allowing its incorporation into proteins and other biological molecules. These organisms form a mutually beneficial relationship with plants, specifically legumes such as soybeans, peas and alfalfa. The symbiotic relationship between Sinorhizobia and legumes requires the function of many proteins; one is 1-aminocyclopropane-1-carboxylic acid (ACC)-deaminase. Bacteria containing ACC deaminase enzymes are more effective in symbiosis due to their ability to lower the concentration of ethylene and bypass the plant defense systems. The goal of this project was to investigate the presence and functionality of ACC deaminase in a collection of Sinorhizobium strains from different locations. Upon examination of the complete DNA sequence of forty- eight Sinorhiziobial strains, eighteen sequences similar to the known ACC-deaminase gene were identified. These proteins had a range of 33 to 100% sequence identity to ACC deaminases (AcdS) from different rhizobia. The functionality of the newly identified proteins was tested using growth assays. These experiments assessed ACC deaminase activity by examining the bacteria’s ability to grow in a medium containing ACC as a sole nitrogen source. The results showed that 70% of the strains examined contained functional ACC deaminases. A biochemical assay was developed and tested to determine its effectiveness at detecting AcdS activity. Preliminary data suggest that the amount of ACC deaminase produced by the strains examined is too low to be quantified under the established assay conditions. Research to optimize the biochemical assays is currently in progress.