One of the major aims of this study was to use genomic approaches to identify bacterial genes involved in iodine transformation.  In support of this goal transposon mutagenesis was used to disrupt genes throughout the genomes of three bacterial isolates from the Hanford Site - Pseudomonas DVZ6, Pseudomonas DVZ24, and Cupriavidus necator DVZ60.   In addition, genomic libraries were constructed using DVZ6 and DVZ60 DNA. Iodide oxidation assays were then performed on the DVZ6 and DVZ60 transposon and genomic libraries.  Whole genome sequencing was performed for Pseudomonas DVZ6, Pseudomonas DVZ24, C. necator DVZ60, and another Hanford Site isolate, Enterobacter hormaechei DVZ29.  The vast majority of mutants of interest (251 out of 268) were of DVZ6 origin, as were the only two genomic clones of interest.  The majority of the genes identified in the study are predicted to encode oxidases, oxidoreductases, transporters, transferases, and reductases as well as hypothetical proteins.  Whole genome sequencing revealed the presence of multiple multicopper oxidase genes, which have been identified as being responsible for iodide oxidation in several other bacteria, in all of the strains investigated, except E. hormaechei DVZ29, which only contained one multicopper oxidase gene.  No multicopper oxidases were identified in any of the functional screens. Redundancy in oxidase function may be a factor in the lack of detection in the mutant libraries.  This may also indicate that there are other pathways that result in iodide oxidation in these terrestrial bacteria. 

Shewanella oneidensis MR-1 is a strain of bacteria known to reduce silver and uranium and has been validated for its potential to serve as an ex-situ bioremediation agent against iodate.  Another goal of the project was to develop and characterize re-engineered ecosystems derived from biofilm-based in vitro models to investigate the activities of these bacteria in enriched communities. For this study, S. oneidensis planktonic and biofilm cultures were cultivated in Tryptic Soy Broth (TSB), a rich and complex growth medium, and in a Glucose based Modified M9 minimal growth medium (GM9). Specifically, the bacterial cultures were investigated for their dissimilatory reduction of iodate (potentially to iodide). Thus S. oneidensis was grown in the presence and absence of iodate. Iodate concentrations were monitored primarily by colorimetric assays with UV Spectrophotometry. Study results demonstrated that both planktonic and biofilm cultures of S. oneidensis could reduce the amount of iodate content in growth medium, by 28% and 30%, respectively, over the course of 24 hours in a fixed-volume system. Furthermore, using Polymath and Matlab software, a kinetics model was developed to determine the rates of S. oneidensis MR-1 growth and iodate-content reduction in TSB and GM9.

A total of thirty-four (twenty-eight undergraduate and six graduate) students, from underrepresented minorities in STEM, were trained in multidisciplinary STEM research while participating in this project. One male graduate student who conducted his PhD dissertation project is now a Project Officer with the US Environmental Protection Agency. Participation in this research project also allowed two women students to successfully complete their Master of Science in Chemical Engineering.  One is currently a PhD candidate in Chemical Engineering at Carnegie Mellon University and the other is a Research and Development Engineering in an American multinational consumer products company. Three of the undergraduate students who participated in the project earned their Bachelor of Science in Chemical Engineering, and 15 earned their Bachelor of Science in Biology at Howard University. One of the undergraduates has now earned two M.S. (in Chemical Engineering and in Forest Biomaterials) from North Carolina State University. Another undergraduate researcher is now a PhD candidate in Chemistry at the University of Chicago. A third undergraduate is now a Process Engineering for a major American chemical company.  Another undergraduate research on the project went on to earn a Master’s in Public Health, and another earned an MS.  Three students are currently medical school students, two are postbaccalaureate fellows, and two others are otherwise pursuing research careers.

In summary, this project successfully identified multiple genes, some shared across bacterial species, that may play roles in iodide oxidation using genomics-based approaches, and generated tools to study other types of iodine transformations, and other relevant topics.  Furthermore, the findings could result in the validation of using planktonic or biofilm cultures of S. oneidensis to develop and design novel microbial bioreactors for the bioremediation of groundwater, soils, and sediments contaminated with toxic metal waste.  The outcomes of the project were disseminated to the Howard University and broader scientific communities through presentations given by the PI, co-PI, and student participants at local, regional, national, and international venues. The project also successfully contributed to the professional development of several individuals from underrepresented groups who are now prepared to enter the STEM workforce. 

Last Modified: 11/29/2023
Modified by: Courtney J Robinson