Extremophiles

Event Date: 
Wednesday, August 26, 2015 - 18:15 - 18:30
Institution: 
CSIRO
Title: 

Effects of temporal pH shifts on ammonia oxidiser community structure and function

Abstract: 

Soil nitrification, the oxidation of ammonia to nitrate, is and driven by bacterial and archaeal autotrophic ammonia oxidisers (AOB and AOA) that carry out the first, rate limiting, step of oxidising ammonia to nitrite.  Previous work has suggested that adaptation and selection in AOA and AOB communities is, to some extent, pH driven.  Acidophilic, acido-neutral, and alkalinophilic groups have been identified by environmental surveys of amoA genes.  These studies of the role of pH in determining ammonia oxidiser community structure and activity have largely relied on spatial pH gradients.  In many managed soil systems (e.g., agricultural systems) edaphic factors (e.g., pH, N concentrations) vary widely temporally and the implications of short term temporal shifts in factors thought to govern oxidiser community structure, and therefore our ability to manipulate edaphic factors to direct community structure, are not well understood.   We investigated the roles of pH in driving nitrifier activity (potential) and community structure over a crop growing season (6 sampling points) in agricultural soils by comparing unamended soils with soils amended with lime to create a temporal pH gradient.  Liming induced a rapid and sustained change in the pH of surface soils (0-10cm), with pH in these soils increasing from 4.8 to 6.5, while in subsurface soils pH increased to a lesser degree after liming (4.3 – 4.5).  After liming, potential nitrification rates increased significantly throughout the production season in both surface and subsurface soils.   TRFLP analysis of total bacterial and archaeal communities showed significant partitioning of the broader communities with soil depth, pH treatment and time, suggesting that microbial communities respond rapidly to changes and that temporal variation in community structure is an important, if often overlooked, factor in assessing microbial diversity patterns. These changes were greater for bacterial, than archaeal, communities. We then utilised amoA gene microarrays to investigate specific AOA and AOB community responses to temporally induced pH changes.  Despite significant changes to ammonia oxidiser function, we saw only very weak changes in community structure of AOA and AOB, suggesting that over shorter temporal periods soil communities are resilient to environmental change and that niche partitioning of ammonia oxidiser communities is likely to be spatially, rather than temporally, governed.

Event Date: 
Wednesday, November 27, 2013 - 18:15 - 18:30
Institution: 
School of Civil and Environmental Engineering, UNSW
Title: 

Metal(loid) bioaccessibility dictates microbial community composition in acid sulfate soil horizons and sulfidic drain sediments

Abstract: 

 
Microbial community compositions were determined for three soil horizons and drain sediments within an anthropogenically-disturbed coastal acid sulfate landscape using 16S rRNA gene tagged 454 pyrosequencing.  Diversity analyses were problematic due to the high microbiological heterogeneity between each geochemical replicate.  Taxonomic analyses combined with measurements of metal(loid) bioaccessibility identified significant correlations to genera (5 % phylogenetic distance) abundances. A number of correlations between genera abundance and bioaccessible Al, Cr, Co, Cu, Mn, Ni, Zn, and As concentrations were observed, indicating that metal(loid) tolerance influences microbial community compositions in these types of landscapes.  Of note, Mn was highly bioaccessible (≤ 24 % total soil Mn); and Mn bioaccessibility positively correlated to Acidobacterium abundance, but negatively correlated to Holophaga abundance and two unidentified archaeal genera belonging to Crenarchaeota were also correlated to bioaccessible Mn concentrations, suggesting these genera can exploit Mn redox chemistry. 

Event Date: 
Wednesday, January 25, 2012 - 19:15 - 20:00
Institution: 
University of Technology Sydney
Title: 

The unusual life and cell cycles of extreme Archaea

Abstract: 

Environments that pose chemical and physical challenges to life generally provide a less competitive habitat to those organisms that can adapt to these “extreme” environments. Of the three domains of life, the Archaea have proven to be the most successful in this regard; some environments are almost exclusively inhabited by archaea, with few or no representatives from the bacterial and eukaryotic domains. Archaea in such environments show some unusual properties that are thought to be related to adaption or a lack of inter-species competition. My research has focussed on the molecular cell biology of two model species of extreme archaea; Sulfolobus solfataricus, which lives in sulphurous hot springs with optimal growth at around 80 C and pH 2-3, and Haloferax volcanii, which lives in high-salt environments such as the salt lakes in Australia and the “Dead” sea in Israel. Genomic and cell cycle studies of these species have shown that genetic multiplicity is a common theme in Archaea. Multiple chromosomes, DNA replication origins, and paralogs of cell-cycle related genes are evident in these species. In this seminar, I will present cell cycle and cell biological studies and I will discuss how the basic cell biological features of archaea might relate to their adaption to extreme environments.

Event Date: 
Tuesday, January 25, 2011 - 19:15 - 20:00
Institution: 
University of California-Davis
Title: 

Gene flow and speciation in populations of bacteria and archaea from a genomic perspective.

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