SHARING MCB SCIENCE: REGULATING NITROGENASE FORMATION IN CYANOBACTERIA

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Cyanobacteria are blue-green colored microbes with a simple cellular structure (like bacteria) and the ability to convert sunlight into chemical energy through photosynthesis (like plants). They also perform nitrogen fixation, a process by which nitrogen is extracted from the air and converted into ammonia, using an enzyme (a specialized protein) called nitrogenase. Since ammonia is a potent plant fertilizer, cyanobacteria can live symbiotically with plants in a variety of soil, water, and marsh habitats – enabling some farmers to use cyanobacteria in place of traditional fertilizers to improve the yields of rice and other staple food crops. Because of its function in nitrogen fixation, research on nitrogenase has the ability to create a firm foundation for future advances in agriculture and food security in support of the NSF’s mission to “…advance the national health, prosperity, and welfare…”

Associate Dean Dr. Teresa Thiel and her lab in the Department of Biology at the University of Missouri – St. Louis study a type of cyanobacteria called Anabaena variabilis. Uniquely, this cyanobacterium has three different nitrogenase enzymes, each capable of performing nitrogen fixation in different environmental conditions. The Thiel team previously studied each of the three nitrogenases and characterized a group of fifteen genes (called the nif1 gene cluster) whose expression through transcription (DNA to RNA) and translation (RNA to protein) is necessary to make the primary nitrogenase in Anabaena variabilis. They also identified potential sites of regulation; cells often regulate discrete steps in the protein production process as a way to conserve cellular resources by limiting the amount of protein produced when it is not needed. For years, scientists knew the important role nitrogenase played in nitrogen fixation, but had yet to uncover how cyanobacterial regulation of production of this important enzyme.

In a recent publication, Dr. Thiel and her team describe their research on one regulatory site called an RNA stem-loop. The investigators predicted this secondary structure would occur before an important gene in the nif1 cluster (called nifH1). The nifH1 gene encodes a protein largely responsible for nitrogenase enzyme assembly and function. Using a process called polymerase chain reaction (PCR) to mutate the RNA stem-loop, they studied how changes in the stem-loop altered nifH1 transcript stability and processing. The Thiel team found that mutations impacting the structure or sequence of the RNA stem-loop also severely inhibited the levels of nifH1 transcript, and most importantly, limited cyanobacteria’s ability to perform nitrogen fixation.

These findings have potential for modulating the efficiency of nitrogen fixation in cyanobacteria, leading to more fertilizer production, and a potential source of renewable energy by harnessing the hydrogen created during nitrogen fixation. This work also may impact an exciting area of bioengineering research. As described in a MCB awarded US and UK research BBSRC-collaboration Ideas Lab proposal, bioengineers are attempting to create a “nitroplast” cellular structure, patterned after the nitrogenase in cyanobacteria, to allow plants to make their own fertilizer.

When asked about the broader impacts of her research, Dr. Thiel responded:

The engagement of scientists with the larger scientific and non-scientific community is critical to promoting a public understanding of science and in attracting students to careers in science. To do so, the broader impacts of my research include integrating research within graduate, undergraduate, and high school education. Students from Jennings Senior High School, a predominantly African-American high school located in North St. Louis County, have participated in 6 weeks of summer research as part of the Jennings at UMSL Program, which is designed to help students succeed in college. Additionally, a student from the UMSL SUCCEED program, which supports vocational experiences for students with intellectual or developmental disabilities works as a laboratory aide in my lab. Furthermore, I participate in educational outreach activities in the St. Louis community, working with local high school teachers to incorporate hands-on microbiology activities in their classrooms.

This work is partially funded by the Division of Molecular and Cellular Biosciences, Award #MCB-1052241.

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