Seminar: "Alternative metal usage in biological nitrogen fixation" - Xinning Zhang

Xinning Zhang, Ph.D.
Associate Professor
Princeton University

Biological nitrogen fixation (BNF), the primary natural source of new bioavailable nitrogen, constrains primary productivity and ecosystem responses to global change. It is catalyzed by the ancient prokaryotic metalloenzyme nitrogenase, which occurs in a molybdenum (Mo)-dependent form as well as “alternative” forms in which vanadium (V) or iron (Fe) replace the active site Mo. Metal bioavailability can vary dramatically over time and space. Nevertheless, environmental BNF has been commonly assumed to rely solely on Mo-nitrogenase, largely due to methodological limitations in quantitatively distinguishing Mo, V-, and Fe-only based BNF rates. Here I will highlight research efforts in my group to (a) develop quantitative tools to probe the differential metal dependency of environmental BNF in modern and ancient contexts; (b) characterize metabolic trade-offs associated with the usage of canonical and alternative nitrogenases in cultured nitrogen fixers; and (c) determine how trace metal and macronutrient bioavailability can interactively constrain BNF in terrestrial ecosystems. The results suggest new avenues to explore free-living and host-associated nitrogen fixer ecophysiology. They also call for consideration of nitrogenase heterogeneity in regional and global N budgets.