Download Nitrogen fixation and its impact in the early evolution of life of Earth

Nitrogen fixation and its impact in the early evolution of life of Earth
Supervisors:
Dr Patricia Sanchez-Baracaldo (School of Biological Sciences and School of Geographical Sciences,
University of Bristol) – Main supervisor
Dr Davide Pisani (School of Biological Sciences and School of Earth Sciences, University of Bristol)
Prof Timothy Lenton (Department of Geographical Sciences, University of Exeter)
Host institution: University of Bristol
Project description: Nitrogen is an essential nutrient whose availability limits the productivity of the
biosphere1, and life on Earth would not have had a chance of diversify without the evolution of
organisms capable of reducing N 2 (which is extremely abundant in the atmosphere but extremely
stable and therefore unusable by the largest majority of organisms) to ammonia, which on the other
hand, can be easily assimilated into living systems. The process of nitrogen reduction to ammonia is
generally known as nitrogen fixation. This key process is carried out by a small number of diverse
prokaryotes including several Eubacteria and the methanogenic Archaeabacteria using enzymes
known as nitrogenases. Several different nitrogenases exist and from a strictly functional point of
view, they differ because they use alternative metallic central atoms (Iron, molybdenum, or
vanadium) in the heterometallic complex defining their active site. While there is strong evidence to
suggest that extant nitrogenases can be traced back to a single ancestor2, it is still unclear which
nitrogenease (Iron, molybdenum, or vanadium) dependent evolved first, and in what order the other
nitrogenases originated. Further to that, it is still unclear when and in what organisms these genes
first emerged and how they spread across the prokaryotes as there is strong evidence that they have
been laterally transferred across distantly related lineages.
Objectives: This project aims to understand how the nitrogenase enzyme complex evolved,
elucidating the origin of nitrogen fixation and the establishment of a key global bigeochemical cycle
(the nitrogen cycle). In particular we shall (1) Investigate relationships among nitrogenase enzymes
and delineate evolutionary patterns (both vertical and horizontal) across prokaryotes. Further to
that (2) we shall attempt establishing what were the first organisms able to carry out Nitrogen
fixation and (3) when in Earth History this process was established by looking at what is known of
the geochemical record (e.g. Nitrogen isotopes).
Gruber, N., and Galloway, J. N. (2008). An Earth-system perspective of the global nitrogen cycle.
Nature 451, 293–296.
Falkowski, P. G. (1997). Evolution of the nitrogen cycle and its influence on the biological
sequestration of CO 2 in the ocean. Nature 387, 272–275