Description: Dr. Joel Griffitts and his team of researchers are analyzing the associations and disassociations between legume roots and bacterial rhizobium cells. This research is an important shift in its field of study, as it looks into deeper problems the two species have in forming a mutual, energy-producing relationship.
Start: June 1, 2006
End: February 29, 2016
- Sponsor: National Science Foundation
- Principal Investigator: Joel Griffitts
Symbiosis categorizes the interaction between two organisms, and which party benefits from the interaction. For example, a parasitic relationship is something like a mosquito siphoning blood, or for a mutualistic relationship, bacteria that help the digestive system and in turn gets to keep some of the food. Multicellular organisms have developed complex processes for detecting and responding to foreign microorganisms. Often these smaller entities are viruses or types of bacteria that are disease-causing pathogens, but at times these microbes offer a beneficial, symbiotic service. Dr. Griffitts is specifically researching the evolved association between legume roots and rhizobium cells—bacteria that fertilize soil by increasing nitrogen levels. In this type of association, the host allows the guest (and its future descendants) to infiltrate its body. Once integrated, legume hosts exchanges organic carbon made in photosynthesis with the guest’s let-off of fixed (accessible) nitrogen.
The foundation for a successful alliance begins with recognition by both parties. Rhizobia sense the chemicals given off by legume roots, which in turn trigger “nod factors” (responding signals) in the rhizobium cells. These nod factors, when molecularly compatible, are like organic passwords that gain them entrance into the system. After “infection”, a swelling— called a nodule— develops on the root and enables the bacteria to convert nitrogen for the plant. However, scientists find that many naturally-occurring strains as well as lab-modified nod factors do not follow through in the long-term; meaning, they may recognize each other, attach, but later prove incompatible when nodules don’t develop or nitrogen is not exchanged. Dr. Griffitts’ investigations seek to understand the factors at a molecular level which control symbiotic compatibility.
Though much research in this field has been conducted over the past few decades, there are still many questions that have not been answered. Dr. Griffitts’ team has decided to try new and innovative paths to decode symbiosis, such as looking at already-incompatible pairs of legumes and rhizobia, and pinpointing the mutant bacteria. This method looks past the initial recognition between the two species, and focus on bacterial genetics and the functions that control late-stage incompatibility. Their current observations are showing that abortive nodulation is conditioned, at least in part, by the host, which may shift research to genetic coding within legumes.
Of special interest should be the fact that these organisms had an evolved alliance, but now are uncooperative. The team hypothesizes several reasons for this incompatibility. One speculation is that perhaps these bacteria have evolved with the strategy to create a parasitic situation— tricking the host into free housing. Another idea is that it was adapted to out-compete other strains for shelter and resources. In time, scientists and agriculturalists may come to see legumes build up immunities to these mutations.
Further research will lead to important understanding about plant defense responses, unsuccessful symbiotic processes, and general host-microbe associations. In time, scientists may unlock the codes of compatibility, and gain greater insight into evolution. The team has already characterized more than a thousand strain-host pairs just within two species, the legume genus Medicago and the rhizobium Sinorhizobium meliloti. Their continued sequence contributions will further molecular analysis and understanding of bacteria and other pathogens. Specific to these organisms, Dr. Griffitts’ work will shed light onto the global nitrogen cycle, and how to magnify world agriculture. Unfortunately, poorer countries do not always have the means to fertilize their fields with nitrogen. Maintaining and increasing rhizobia amounts in the soil will help countries introduce new crops, and yield greater harvests. Another effect of enhancing legume crops is that it will decrease fossil fuel consumption brought on by industrial fertilizer production, which consumes an important 2% of the world’s energy production all by itself.
Lastly, these studies have the potential to expand well-beyond the science community. An important educational goal of the project is to create the Symbiosis Learning Consortium (SymLC). This program will focus on inquiry and experimentation as means of teaching high school students, undergraduates, and professionals. The program hopes to aid in analyzing strains and demonstrate fundamental scientific processes for its participants. Housed in the BYU Department of Microbiology and Molecular Biology, the SymLC will take existing courses and use rhizobium-legume symbiosis as the focus for teaching many biology principles. By reaching out to a larger community, the SymLC may also encourage high school and undergraduate students to pursue degrees and careers in science.