OOS 39-9
Investigating the associative nitrogen-fixing bacteria for sustainable production of switchgrass

Wednesday, August 12, 2015: 10:50 AM
316, Baltimore Convention Center
Richard R. Rodrigues, Genetics, Bioinformatics, and Computational Biology, Virginia Tech., Blacksburg, VA
Bingyu Zhao, Department of Horticulture, Virginia Tech., Blacksburg, VA
Mark Williams, Horticulture, Virginia Polytechnic and State University, Blacksburg, VA

Nitrogen is abundant in the atmosphere. However, plants can only utilize it in the forms of ammonia and nitrates. Hence, many non-legume plants, especially grasses, have nitrogen as their limiting nutrient, severely impacting biomass yield. Chemical based nitrogen-fertilizers provide accessible nitrogen to plants. However, they are expensive, with majority being lost leading to soil and water pollution [1].

Diazotrophs are bacteria that can convert the atmospheric nitrogen to ammonia, a process called as “nitrogen fixation”. These bacteria are a natural and an eco-friendly alternative to the nitrogen-based chemical fertilizers. Three-year field studies indicate upto 50% of nitrogen is obtained from nitrogen fixation in switchgrass and other high productivity grasses. Switchgrass (Panicum virgatum L.) is a native, warm-season, perennial tall grass, primarily used as forage and feedstock for biofuel. ‘Alamo’ and ‘Dacotah’ are cultivars of switchgrass, adapted to the southern and northern US eco-types respectively [2]. We hypothesize that the high biomass yielding, faster and taller growing Alamo has more nitrogen demands than Dacotah and supports bacterial communities with high rates of nitrogen fixation in the root-zones. As such, these cultivars offer a system to study the nitrogen-fixing bacteria associated with plants of contrasting nitrogen requirements.


At stage V2 of the vegetative growth phase, Alamo showed ~3.6 times higher nitrogen fixation rates than Dacotah. In addition, we observed differences in absolute and relative abundance of soluble free amino acids, abundance and composition of cultivable diazotrophs between cultivars. Aspartic acid and Glutamic acid, known to be important signals in nitrogen fixation [3], were correlated with Alamo and Dacotah respectively. Meta-genomic and -transcriptomic studies will help to identify the full suite of structure and function of bacterial communities associated with these cultivars.


1. Sutton, M.A., et al., Too much of a good thing. Nature, 2011. 472(7342): p. 159-61.

2. Zalapa, J.E., et al., Hierarchical classification of switchgrass genotypes using SSR and chloroplast sequences: ecotypes, ploidies, gene pools, and cultivars. Theor Appl Genet, 2011. 122(4): p. 805-17.

3. Lodwig, E.M., et al., Amino-acid cycling drives nitrogen fixation in the legume-Rhizobium symbiosis. Nature, 2003. 422(6933): p. 722-6.