Chemistry

Event Date: 
Tuesday, July 24, 2012 - 18:00 - 18:15
Institution: 
University of NSW
Title: 

Bioremediation of Mixed Chlorinated Solvents by Combining Two Biogeochemical Processes

Abstract: 

Chloroethenes are a class of chlorinated solvents which cause extensive soil and groundwater contamination worldwide. They can be detoxified by anaerobic dehalogenating bacteria, in the process of reductive dechlorination.  However, chloroethenes are often found mixed with chloromethanes, a class of solvents which inhibit the enzymatic detoxification of chloroethenes by dehalogenating strains.  Iron sulfides are powerful chemical reductants for the dechlorination of chloromethanes, and can be generated through the metabolism of iron- and sulfate-reducing bacteria. In this study, a sulfate reducing bacterium was used to produce iron sulfide in the presence of moderate levels of tetrachloroethene and carbon tetrachloride to examine the ability of a sulfate reducing organism to drive reduction of a chloromethane in the presence of chloroethene.

 

Cultures of the sulfate-reducer Desulfovibrio vulgaris were established in the presence of 100 µM each of tetrachloroethene and carbon tetrachloride. Growth, sulfide formation and chlorinated solvents and their dechlorinated products were monitored. The effects of amorphous iron oxide and cyanocobalamin on the fate of chlorinated solvents compared with unamended control cultures were investigated. 

Following growth and sulfide formation, carbon tetrachloride was dechlorinated mostly to carbon disulfide while tetrachloroethene was dechlorinated to trichloroethene and acetylene.  Dechlorination rates were enhanced both by the presence of iron and cyanocobalamin separately, and significantly increased when both were present.

This study illustrates the potential to use sulfate reducing bacteria in zones of mixed chlorinated solvent groundwater pollution in order to produce iron sulfide minerals. Their cyanocobalamin-catalyzed action on chloromethanes, coupled with that of dehalogenating strains on chloroethenes is a promising strategy for the bioremediation of such contaminated areas."

Event Date: 
Wednesday, June 27, 2012 - 19:15 - 20:00
Institution: 
Faculty of Agriculture & Environment, University of Sydney, Sydney, NSW.
Title: 

Sulfur cycling in the rhizosphere: the role of sulfatase and sulfonatase diversity.

Abstract: 

Growth of healthy, high-yielding crop plants requires a stable input not only of nitrogen and phosphorus, but also of sulfur (S). Although S is naturally present in soils, it is usually bound in organic form as sulfate esters or sulfonates, which are not directly bioavailable to plants. Sulfur can be supplemented by addition of inorganic fertilizer, but most sulfate for plant nutrition is provided by microbial turnover of organically-bound sulfur. To identify the rhizosphere organisms responsible for this turnover, we focused on the key genes atsA, which encodes arylsulfatase, and asfA, which is required for aryldesulfonation. Functional T-RFLP analysis was used to analyse atsA diversity in a range of agricultural and natural soils, and clear atsA community differences associated with land use and soil/bedrock types were observed, which were mirrored in the arylsulfatase activity of the cultivable fraction of the population. Soil arylsulfatase activity is routinely assayed as a measure of soil health, but these data highlight the need for detailed studies on arylsulfatase gene diversity in the soil. Sulfonatase diversity was measured in rhizospheres of field-grown wheat plants and in a sulfate-limited Agrostis-dominated grassland, and the effect of adding sulfate in long-term or short-term treatments was tested. Functional asfA community analysis showed that desulfonation genes from both wheat and Agrostis rhizospheres were dominated by Variovorax and Polaromonas species. This distribution of taxa was also found in a cultivation-dependent analysis, and these genera appear to be key players in rhizosphere sulfonate transformations in several environments. Increasing our understanding of the rhizosphere microbes that catalyse soil organosulfur turnover will allow us to develop management practices to maximize soil sulfur availability, and minimize the costs associated with fertilization.

Event Date: 
Tuesday, April 24, 2012 - 18:00 - 18:15
Institution: 
University of Georgia
Title: 

Bioluminescence: The First 3000 Years

Abstract: 

Bioluminescence along with astronomy, is one of the oldest subjects of scientific investigation.  Light from fireflies is mentioned in ancient Chinese poetry and later more systematic studies are in the writings of Aristotle and Pliny the Elder.  In the modern era, Robert Boyle in a 1672 Proc. Roy. Soc. paper, reported the requirement of bacterial bioluminescence for air, now known to be oxygen.  His paper contained the first published Table of experimental results.  In 1876 Dubois reported that the living light from the bioluminescent clam, could be extracted into solution.  He showed that bioluminescence was just a chemical reaction, an enzyme and substrate, which he dubbed “luciferase” and "luciferine".  In 1947, McElroy reported that Dubois' substrate was actually ATP.  Genuine firefly luciferin was not purified and structurally characterized until 1959.  In 1962, Shimomura noted the presence of a “green protein” in extracts of the bioluminescent jellyfish.  10 years later this was named “Green-fluorescent protein” (GFP), now the most famous protein in Science and the basis of Shimomura’s Nobel prize in 2008.
In the last two decades we have applied biophysical methods: picosecond dynamic fluorescence spectroscopy, NMR, and structural biology, for uncovering bioluminescence mechanisms.  I will show how this most primitive organism, the jellyfish, early discovered the most advanced physics, quantum correlation, to generate its characteristic green bioluminescence.

Event Date: 
Wednesday, March 28, 2012 - 18:15 - 18:30
Institution: 
Macquarie University
Title: 

Making and breaking dimethylsulfide in salt marsh sediments

Abstract: 

DMSP (dimethylsulfoniopropionate) is a key organic compound in the sulfur cycle with ~10^9 tons of this anti-stress compatible solute being made each year by marine phytoplankton, macro-algae and some salt marsh plants. The DMSP that is liberated is catabolised in a series of different microbial reactions that comprise a massive set of biotransformations in the global sulfur cycle. Some of the reaction products, such as DMS (dimethylsulfide), have major environmental consequences in their own right, from climate regulation to animal behaviour. Our work investigates microbial populations that cycle DMSP and DMS in coastal intertidal sediments. Combining geochemical and molecular biological approaches, such as stable isotope probing (SIP) and targeted high throughput sequencing, we are identifying the main microbial players that catabolise DMSP and DMS in oxic and anoxic parts of intertidal sediments alongside the key genes and cognate biochemical pathways that contribute to the turnover of these influential molecules. Early work led to the observation of a vertical microbial population structure within the salt marsh sediment, partially linked to the sulfur cycle biochemistry of this ecosystem. SIP experiments are allowing the characterisation of active microbial processing of DMSP and DMS compounds by separate new bacterial groups, closely associated to salt marsh plants and within the oxic sediment layer. This work is filling in major gaps in our knowledge of the global organic S cycle and the role of microbial populations in major environmental biochemical processes.

Event Date: 
Wednesday, January 25, 2012 - 18:15 - 18:30
Institution: 
UNSW
Title: 

The impact of petroleum hydrocarbons on microbial diversity in a sub-Antarctic soil; a proxy for soil health

Abstract: 

Anthropogenic sources of contamination remain a legacy throughout the Antarctic Region, with the majority of contamination occurring alongside concentrated human activities at research stations. At Macquarie Island, an Australian Sub-Antarctic territory we have been investigating the impact of petroleum hydrocarbon contamination in the form of Special Antarctic Blend (SAB) diesel fuel on the microbial ecology of sub-Antarctic soils. Whilst bioremediation strategies are currently underway on the Island, there is a lack of petroleum hydrocarbon contamination guidelines specific to Antarctic or sub-Antarctic regions. Additionally, there is insufficient site-specific toxicity data available for remediation end points to be established. Therefore, we have assessed the bacterial and fungal response to increasing concentrations of SAB diesel fuel through a combination of novel culturing methods, flow cytometric analysis of cell numbers and massively paralley pyrosequencing targeting the 16S and ITS genes. Results of this investigation will provide the scientific basis for understanding how much fuel is too much and how clean is clean enough?

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).

Event Date: 
Wednesday, June 29, 2011 - 18:00 - 18:15
Institution: 
UNSW
Title: 

Metabolic methanisation of chloroform by a three component microbial community.

Abstract: 

Chloroform is a highly toxic organochlorine found in subsurface environments due to its poor handling and disposal techniques by industry. Bioremediation of organochlorine polluted environments is a well established technique that utilises dehalogenating bacteria to reductively dechlorinate organochlorines to their hydrocarbon counterpart. One drawback of bioremediation is that chloroform is inhibitory to this microbial process. A key to the advancement of the bioremediation industry is the discovery of dahalogenating bacteria capable of complete chloroform metabolism.

Here we report for the first time a microbial population capable of rapid metabolic transformation of chloroform at high concentrations (~50 ppm) to methane. Cultures were established with sediment sampled 4.5 m below ground surface from an aquifer polluted for over 40 years with a mixture of organochlorine compounds. A combination of functional data, pyrosequencing, quantitative PCR and the application of labelled substrates were used to elucidate the participating microbial community members. Members of the Dehalobacter genus were found to first dehalo-respire chloroform to dichloromethane which was then fermented to formate and acetate. A hydrogenotrophic syntroph (i.e. a methanogen) was then required to drive this process forward to methane.

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