Water

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

Divergence in temperature stress management between coastal and East Australian current (EAC) phytoplankton populations.

Abstract: 

In June 2015, 27 scientists took part in a 3 week ocean voyage aboard the brand new Australian research vessel, the RV Investigator. The main objective of the expedition was to study sub-mesoscale processes - billows and eddies - along the productive shelf influenced by the East Australian Current. Dr Olivier Laczka is presenting the results obtained for one of the multiple projects conducted during this voyage. Microbial communities from the EAC and a coastal site (north of Smokey Cape) were incubated along a temperature gradient (spanning 32 to 15.5 °C) to examine their capacity to deal with departures from in situ temperature (~22 °C). Intracellular stress within picoeukaryote populations was examined using a fluorescent stain targeting Reactive Oxygen Species (ROS). Stained samples were examined with a flow cytometer (excitation wavelength 488 nm). The goal of this study was to assess whether EAC microbial communities are more thermally tolerant than coastal microbial communities and determine whether general oxidative stress patterns could be used as a signature of water mass origins.

Event Date: 
Wednesday, September 30, 2015 - 18:00 - 18:15
Institution: 
Macquarie University
Title: 

Aquifer microbial community assembly: do neutral processes dominate?

Abstract: 

Community assembly processes can be condensed into four categories: dispersal, selection, drift and speciation. We tested aquifer communities (of Archaea, Bacteria, Fungi, and Eukarya generally) for evidence that dispersal limitation and environmental selection play a role in determining community biodiversity and composition. We found only weak evidence for these processes at a regional scale of up to 250 km and spanning several significant dispersal barriers. I discuss the possibility that neutral (i.e. non-deterministic, non-selective) processes dominate in groundwater ecosystems, and the spatial scaling of these processes.

 

Event Date: 
Wednesday, July 29, 2015 - 18:15 - 18:30
Institution: 
Australian Institute of Marine Sciences
Title: 

Coral Reefs Go Viral: Unveiling the viruses associated with corals in a changing climate.

Abstract: 

Viruses are the most common biological agents in the global oceans, with numbers typically averaging ten billion per litre. The ability of viruses to infect all organisms indicates they most likely play a central role in marine ecosystems and have important consequences for the entire marine food web. Marine viruses influence many biogeochemical and ecological processes, including energy and nutrient cycling, host distribution and abundance, and horizontal gene transfer events. Research into viruses associated with coral reefs is a newly emerging field. Corals form an obligate symbiotic relationship with the dinoflagellate genus Symbiodinium, upon which the coral relies heavily for nutrition and calcification. Disruption of this symbiosis can lead to loss of the symbiotic algae from their host, resulting in coral bleaching and, if the symbiosis cannot re-establish, death of the coral colony. While a number of factors, including elevated reactive oxygen species production by Symbiodinium have been linked to coral bleaching, viral infection has not been methodically examined as a possible cause. Viruses that potentially target the algal symbiont, Symbiodinium sp., have been reported previously; therefore, we examined whether Symbiodinium in culture is host to a virus that switches to a lytic infection under stress, such as UV exposure or elevated temperature. Analysis of algal cultures, using techniques including flow cytometry and transmission electron microscopy, revealed prevalent viral activity, regardless of experimental conditions. This talk will present recent results and results allow for the development of molecular diagnostic probes for rapid detection of viruses in field samples, and will help monitor and assess the role of viruses in coral bleaching and holobiont functioning.

Event Date: 
Wednesday, February 25, 2015 - 18:00 - 18:30
Institution: 
San Diego State University
Title: 

Integrating microbial community dynamics into kelp forest ecosystem models

Abstract: 

Metagenomics has enabled a greater understanding of microbial community dynamics than previously realized and now the challenge is to integrate microbial dynamics into ecological models. My lab takes an ‘omics approach mixed with classical microbiology to identify factors affecting microbial communities and how an altered microbial community will affect macro-organism health and ecosystem functioning. The key habitats are coral reefs and kelp forests. Within the kelp forest, we have started with a culturing approach that has identified novel genomes associated with the giant kelp Macrocystis pyrifera. Phenotypic assessments of these bacteria have identified increase in the microbe’s ability to tolerate copper and resist antibiotics with increasing human activities. We have tested the effects of altered microbial abundance and community composition on survival and development of M. pyrifera gametophytes. Decreasing microbial abundance enhanced M. pyrifera recruitment, increasing zoospore settlement and gametophyte development. Gametophytes reared in microbial communities sampled adjacent to the populated city showed lower survival and growth compared to gametophytes in microbial communities from a remote island. Metagenomics revealed a high abundance of phototrophic and oligotrophic microbes from the island, compared with an abundance of eutrophic microbes adjacent to the city. In addition, microbes adjacent to the city lacked genes that produce quorum signaling molecules, negatively influencing kelp spore settlement. Long term analyses of the microbial communities from the kelp forest have been initiated and we are currently investigating the microbes associated with the water column and kelp surface at two distinct depth. First, at 0.5 m depth where the water is warmer, highly oxygenated and receiving large amounts of carbon from photosynthesis and second, at 15 m depth where the water is under seasonal thermocline, colder, lower in oxygen, and can potentially be exposed to high partial pressure of carbon dioxide. Monthly sampling has revealed microbial number is lower at depth and pCO2 is higher. Metagenomic analysis of these samples is under way. Kelp feeds the ecosystem through degradation and we are currently investigating the effects of microbes on kelp degradation and subsequent nutritional value. We have shown altered microbial communities are detrimental to kelp recruitment and are identifying way of adding these data to ecosystem models.

Event Date: 
Wednesday, February 26, 2014 - 18:30 - 19:00
Institution: 
Australian Institute of Marine Science
Title: 

A microbial perspective of coral from the Great Barrier Reef

Abstract: 

Coral reefs are fundamental in providing ecological, social and economical benefits to local communities, governments and nations. In Australia, the Great Barrier Reef is an iconic symbol in our national psyche, representing approximately 17% of the global tropical coral reef area with an estimated economic value at greater than AUD$5 billion per year. Coral reefs are constructed through the close association between reef building corals and their symbiotic dinoflagellate microalgae (Symbiodinium). However just as in other animal systems, corals are now thought of as a holobiont, forming additional close and intricate associations with a range of other microbial organisms such as bacteria, archaeae, fungi and viruses. Over the last decade a greater understanding has been obtained in how corals shape and structure their microbial partners, providing important functional roles in maintaining overall coral fitness. The cycling of nitrogen and sulfur compounds within the holobiont are increasingly being recognised as driving many of these coral microbial associations and have important consequences for coral health and the subsequent resilience of coral reefs. For example, nitrogen fixing bacteria (diazotrophs) within the Rhizobia group, which accomplish nitrogen fixation after establishing symbiosis in the roots of host plants, also appear common and specific to corals. These associations are established at the earliest larval life stages and maintained as the coral grows in mature colonies. Using fluorescence in situ hybridization (FISH) and nanoscale secondary ion mass spectrometry (NanoSIMS) the uptake of diazotrophic bacteria and passage of nitrogen into coral larvae can be observed, providing evidence that diazotrophs can provide an additional nitrogen source to the animal. Reef-building corals are the most prolific producers of dimethylsulphoniopropionate (DMSP), a molecule central in the marine sulphur cycle and precursor of the climate-active gas dimethylsulphide (DMS). Recent work has shown that the coral animal itself can produce DMSP, hence overturning the paradigm that photosynthetic organisms are the sole biological source of this compound. DMSP represents a rich nutrient source for bacteria with diversity surveys highlighting an extensive overlap between bacterial species associated with corals and species implicated in the degradation of dimethylsulfoniopropionate (DMSP). Again using FISH and NanoSIMS approaches, this close interaction between corals, their Symbiodinium partners and associated bacteria can be visualised. Interestingly, through the metabolism of DMSP, a Pseudovibrio sp. commonly associated with corals produced tropodithietic acid (TDA), a sulfur-containing antimicrobial which is suspected to act in protecting corals from invasive microbial species. Anthropogenic stresses such as increased sea surface temperatures, nutrient input and sedimentation can shift these coral-microbiota associations, thereby contributing to reduced coral fitness. For example, production of TDA by the coral associated Pseudovibrio sp.was significantly reduced at higher temperatures potentially reducing the protective effect the compound can provide the coral holobiont. Temperature stress also causes shifts in coral associated microbial communities, with a metagenomic approach demonstrating a shift in the microbial community away from autotrophy and an increase in virulence associated genes. Coral diseases are on the rise with disease outbreaks contributing to significant loss of both key reef organisms and coral cover. Recent assessments have documented sharp declines in coral reefs globally, therefore an understanding of the microbial factors that underlie coral health and fitness are paramount.

Event Date: 
Wednesday, September 25, 2013 - 06:00 - 06:15
Institution: 
UNSW
Title: 

Viral infections of Ecklonia radiata

Abstract: 

 
Ecklonia radiata the dominant habitat-forming seaweed in temperate Australia has experienced high rates of mortality in the last decades. Disappearance of this kelp forest would have serious consequences for the marine ecosystem. The causes of mortality are not yet understood but we hypothesise a combination of environmental stress and viral infection. We could demonstrate that disease symptoms such as discolouration and bleaching are widespread but patchy distributed around Australia, which does not correlate simply with latitudinal variation in water temperatures. Focussing on the Kelp populations along the highly urbanised coast of Sydney we observed a highly site-specific pattern in the frequency of disease symptoms in E. radiata populations. Photosynthetic activity of discoloured thalli was significantly reduced compared to co-occurring, healthy (dark brown) thalli. Moreover, we were able to demonstrate that discoloured tissue from Ecklonia radiata from multiple sites around Sydney were infected with a viral pathogen. Inoculation experiments in the laboratory with the extracted viruses of sick tissue resulted in infection of healthy tissue of Ecklonia radiata. The frequency of putative disease morphotypes, and the relative abundance of viruses in Ecklonia radiata around Sydney appear to be higher at sites that are impacted by untreated wastewater discharge.  

Event Date: 
Wednesday, July 31, 2013 - 18:15 - 18:30
Institution: 
University of Technology Sydney
Title: 

The Sydney Harbour microbiome: bacterioplankton diversity and dynamics

Abstract: 

Sydney Harbour and its surrounding coast is an iconic habitat that supports a diverse ecosystem however the composition and dynamics of bacterioplankton in the system remain a major knowledge gap. The harbour and coast also provide a model system for investigating the spatiotemporal distribution of microorganisms across multiple physicochemical gradients and their response to anthropogenic input. Using next-generation DNA sequencing, we provide a comprehensive profile of microbial communities from a range of habitats inside the harbour and show strong biogeographic patterns in taxonomic composition.  Using network analysis to visualize correlations between community structure and environmental variables we have identified the key drivers of community partitioning. Combined these results lead to a more detailed understanding of the diversity and roles of bacterioplankton in Sydney Harbour and its surrounds, and provide insight into marine microbial ecology generally. 

Event Date: 
Wednesday, May 29, 2013 - 19:00 - 19:45
Institution: 
CSIRO
Title: 

Sediment Biobarriers for Chlorinated Aliphatic Hydrocarbons in Groundwater Reaching Surface Water

Abstract: 

 
This study explored the potential of eutrophic river sediments to attenuate the infiltration of chlorinated aliphatic hydrocarbon (CAH)-polluted groundwater discharging into the Zenne River near Brussels, Belgium. Active biotic reductive dechlorination of CAHs in the riverbed was suggested by a high dechlorination activity in batch- and column biodegradation tests performed with sediment samples, and by the detection of dechlorination products in sediment pore water. Halorespiring Dehalococcoides spp. were present in large numbers in the riverbed as shown by quantification of their 16S rRNA and reductive dehalogenase genes. By using DGGE-fingerprint analysis of relevant nucleic acid markers, it was shown that the Zenne River sediments were inhabited by a metabolically diverse bacterial community. A large diversity of sulfate-reducing bacteria, Geobacteraceae and methanogens, which potentially compete with halorespiring bacteria for electron resources, was identified. The high organic carbon level in the top of the riverbed, originating from organic matter deposition from the eutrophic surface water, resulted in a homogeneous microbial community structure that differed from the microbial community structure of the sediment underneath this layer. Monitoring of CAH concentrations and stable isotope ratios of the CAHs (δ13C) and the water (δ2H and δ18O), allowed to identify different biotic and abiotic CAH attenuation processes and to delineate their spatial distribution in the riverbed. Reductive dechlorination of the CAHs was the most widespread attenuation process, followed by dilution by unpolluted groundwater discharge and by surface water-mixing. During a 21-month period, the extent of reductive dechlorination ranged from 27 to 89% and differed spatially but was remarkably stable over time, whereas the extent of abiotic CAH attenuation ranged from 6 to 94%, showed large temporal variations, and was often the main process contributing to the reduction of CAH discharge into the river. Although CAHs were never detected in the surface water, CAHs were not completely removed from the discharging groundwater at specific locations in the riverbed with high groundwater influx rates. Therefore, it was concluded that an increase in the extent of biotransformation in the riverbed is needed for acceptance of the Zenne biobarrier as a viable remedial option for attenuation of discharging CAH-polluted groundwater.

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