Nitrogen fixing potential in extreme environments

• Main Author: Sorek Abramovich, Reut
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: UNSW Sydney 2013
• Subjects: Nitrogen; Stromatolites; Extremophile; nifH; Amorphous Glacier; Bray; Terra Nova Bay; Antarc*; Antarctica; ice core
• Online Access: https://dx.doi.org/10.26190/unsworks/16288; http://hdl.handle.net/1959.4/52826

Biological nitrogen fixation is a key process in providing accessible nitrogen to Earth s biosphere. This process has been studied in various habitats yet extreme environments still remain relatively unexplored. The nifH gene codes for the Fe protein component in the nitrogenase, which facilitates the nitrogen fixation. Our aims in this study were to assess diazotrophic diversity, richness and community structure in three unique environments and analyse potential adaptations in the Fe protein composition and structure. Our methods included a terminal-restriction fragment length polymorphism (T-RFLP) analysis on 16S rDNA, PCR amplification of the nifH gene, statistical t-test analysis of amino acid compositions, a novel evolutionary analysis and 3D modelling with the I-TASSER web server. Boulder Clay and Amorphous Glacier are two ice-free areas in Terra Nova Bay, Antarctica, which differ in their geological origins and physio-chemical properties. DNA yields from ice-core samples ranged from 0.29 ng L-1 in Amorphous Glacier to 88 ng L-1 in Boulder Clay. Bray-Curtis cluster analysis suggested Boulder Clay bacterial profiles were similar to each other, but cluster separately from Amorphous Glacier. The hypersaline (>70 ppt) bays of Shark Bay, Western Australia, are home to the stromatolites microbial mats. The microbial diversity of diazotrophs from two different years, 1996 and 2004, was investigated. Our analysis indicated columnar stromatolites included a common persisting cyanobacterial diazotroph, a Cyanothece or Xenoccocous. Both samples contained novel nifH gene sequences of low similarity to uncultured nifH clones from saline to hypersaline environments, and their inferred NifH amino acid sequences were highly similar to unicellular, non-heterocystous Cyanobacteria and γ,-Proteobacteria sequences. Paralana s hot radon springs (PHS, 57 C°) are situated in South Australia. Phylogenetic analysis indicated a rich and diverse group of amino acid NifH sequences from α-, γ-, and δ-Proteobacteria, Chloroflexi and Cyanobacteria phyla. These results suggested aerobic and anaerobic bacteria with conventional Mo nitrogenase might be involved in nitrogen fixation. Our bioinformatic analysis suggested that halophilic adaptations, with an increase in salt bridges, acidic residues and a decrease in bulkier hydrophobic amino acids, did occur in stromatolite diazotrophs and that partial thermophilic adaptations, mainly an increase in salt bridges, Pro and charged residues, did occur in the PHS diazotrophs. These studies provide new insight on the ongoing evolution of nitrogen fixation in extreme environments.