Plant physiology

Event Date: 
Wednesday, October 28, 2015 - 18:15 - 18:30
Institution: 
UTS
Title: 

Heterogeneity in diazotroph diversity and activity within a putative hotspot for marine nitrogen fixation

Abstract: 

Australia’s tropical waters represent predicted “hotspots” for nitrogen (N2) fixation based on empirical and modelled data. However, the identity, activity and ecology of N2 fixing bacteria (diazotrophs) within this region are virtually unknown. By coupling DNA and cDNA sequencing of nitrogenase genes (nifH) with size fractionated N2 fixation rate measurements, we elucidated diazotroph dynamics across the shelf region of the Arafura and Timor Seas (ATS) and oceanic Coral Sea during Austral spring and winter. During spring, Trichodesmium dominated ATS assemblages, comprising 60% of nifH DNA sequences, while Candidatus Atelocyanobacterium thalassa (UCYN-A) comprised 42% in the Coral Sea. In contrast, during winter the relative abundance of heterotrophic unicellular diazotrophs (∂-proteobacteria and gamma-24774A11) increased in both regions, concomitant with a marked decline in UCYN-A sequences, whereby this clade effectively disappeared in the Coral Sea. Conservative estimates of N2 fixation rates ranged from < 1 to 91 nmol L-1 d-1, and size fractionation indicated that unicellular organisms dominated N2 fixation during both spring and winter, but average unicellular rates were up to 10-fold higher in winter than spring. Relative abundances of UCYN-A1 and gamma-24774A11 nifH transcripts negatively correlated to silicate and phosphate, suggesting an affinity for oligotrophy. Our results indicate that Australia’s tropical waters are indeed hotspots for N2 fixation, and that regional physicochemical characteristics drive differential contributions of cyanobacterial and heterotrophic phylotypes to N2 fixation.

Event Date: 
Wednesday, October 28, 2015 - 18:00 - 18:15
Institution: 
UNSW
Title: 

Key to living in the extreme desert soils of eastern Antarctica: a chemolithotrophic lifestyle

Abstract: 

Mitchell Peninsula is located at the south of the Windmill Islands, Eastern Antarctica. It is described as a nutrient poor, extreme polar desert and limited knowledge on the microbial diversity of  the soils in this area exists. We examined the microbial taxonomic composition and metabolic potential of Mitchell Peninsula soils  using 16S metagenomics and shotgun metagenomics. We found the site to be a potential biodiversity hotspot, containing a high abundance of Candidate Phyla WPS2 and AD3. Subsequently, differential binning was used to recover 23 draft genomes, including 3 genomes from WPS-2 and two from AD3.  Further analysis of the metagenome revealed a novel Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) gene to be abundant in the bacterial community, despite a lack of evidence for photosynthesis related genes. We believe that unlike many other Antarctic regions, chemolithautrophic carbon fixation via CBB cycle is the dominant carbon fixation pathway, hence this pathway is providing the key to survival is this very dry, hostile environment. 

Event Date: 
Wednesday, April 27, 2011 - 18:15 - 18:30
Institution: 
UNSW
Title: 

The first chlorophyll to be discovered in 60 years: chlorophyll F.

Abstract: 

This remarkable compound, found in stromatolite-inhabiting cyanobacteria from Shark Bay, Western Australia, can absorb light further in the red region of the electromagnetic spectrum than any of the other known chlorophylls.
This work was a truly collaborative effort between Sydney-based (University of New South Wales, the University of Sydney and Macquarie University) and international researchers (University of Munich).

Syndicate content