Date of Award

Spring 2013

Degree Type

Honors Project


College of Liberal Arts

First Advisor

Martinez-Vaz, Betsy M.


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 symbiosis with legume plants such as peas, soybeans, and alfalfa. The symbiotic relationship between Sinorhizobia and legumes requires of the function of many proteins; one is 1- aminocyclopropane-1-carboxylic acid (ACC)-deaminase. Bacteria containing ACC-deaminase enzymes are more effective in nodulation due to their ability to lower the concentration of ethylene and bypass the plant defense systems. Upon examination of the complete DNA sequence of forty-eight Sinorhiziobia strains from different geographical locations, eighteen sequences similar to known ACC-deaminase genes were identified. Ten strains had homologs with between 70 and 99% identity, and eight with ~30% identity (designated AcdS3) to ACCdeaminase from R. leguminosarum v. viceae. The goal of this project was to investigate the functionality and substrate specificity of ACC-deaminase homologues in Sinorhizobium strains. ACC-deaminase homologues were tested using biochemical assays and growth assays for ACCdeaminase and D-cysteine desulfhydrase activity. Protein alignment and comparative 3D modeling of pyridoxal-5’-phosphate (PLP) active sites suggest that the AcdS3 homologue may lack enzymatic activity due to an absence of hydrogen bonding from a glycine residue to the nitrogen atom of PLP. Preliminary data from biochemical assays for ACC-deaminase and Dcysteine desulfhydrase activity support a lack of functionality of homologs for both enzymes.








Departmental Honors Project

Included in

Biochemistry Commons