Physical geography

Event Date: 
Wednesday, May 27, 2015 - 18:15 - 18:30
Institution: 
University of Western Sydney & Macquarie University
Title: 

Structure, diel functional cycling and viral ecological filtering in the microbiome of a pristine coral atoll in the Indian Ocean

Abstract: 

Given the role of microbes as both indicators and drivers of ecosystem health, establishing baselines in pristine environments is crucial to predicting the response of marine habitats to environmental change.  Here we describe a survey of microbial community composition and metatranscriptomic gene expression across the Indian Ocean, encompassing the first samples from the pristine Salomon Atoll in the Chagos Archipeligo.  We observed strong patterns in beta-diversty  which reflected  Longhurst biogeographical  provinces established  using primary productivity and thermohaline properties of ocean currents.  Samples from within Salomon Atoll showed a highly unique community which was remarkably different even from adjacent samples despite constant water exchange.  This pattern was driven by the dominance of the photosynthetic cyanobacterium Synechococcus within the lagoon, the diel activity of which was responsible for driving shifts in the transcriptional profile of samples.  Inside the lagoon, increases in the expression of genes related to photosynthesis and nutrient cycling associated with the bottom-up control of bacterial populations, however the expression of viral proteins increased five-fold within the lagoon during the day, indicating a concomitant top-down control of bacterial dynamics byphage.  Indeed, genome recruitment against Synechococcus reference genomes suggested  viruses  provide  an  ecological filter for determining the diversity patterns in this system. This study also represented a proof of concept for  using a ‘citizen oceanography’ approach utilzing tools that may easily be adapted to deployment on any ocean going yacht, greatly expanding the scale and outreach of marine microbiology studies. 
 

Event Date: 
Wednesday, July 30, 2014 - 18:00 - 18:15
Institution: 
UTS
Title: 

Exploring coral-bacteria interactions: where are they, how do they get there and what do they do?

Abstract: 

Microorganisms live in tight ecological associations with corals, but microbial community composition, functions and behaviours within coral reef ecosystems are not yet fully understood. To examine the community structure, metabolic capacity and the potential role of chemotaxis in the ecology of coral reef bacterial communities, we performed a suite of laboratory, in-situ and thermal stress experiments on Heron Island, the Great Barrier Reef (GBR). To characterise patterns in microbial composition and metabolic capacity across different niches on a coral reef, metagenomes were sequenced from seawater samples associated with the surfaces of corals, the sandy substrate and in open water, outside of the reef. Within these environments we also examined the potential ecological role of chemotaxis among coral associated bacteria, by using laboratory and in situ chemotaxis assays to test for levels of chemotaxis towards several chemoattractants known to be released by corals and their symbiotic dinoflagelletes including amino acids, carbohydrates, ammonium chloride, and dimethylsulfonopropionate (DMSP). Finally, to determine how environmental variability, specifically thermal stress, influences bacterial community composition, behaviour and metabolic capacity, manipulation experiments were conducted using Pocillopora damicornis in flow-through aquatic systems on Heron Island.
 We found that the composition and metabolic potential of coral reef bacteria is highly heterogeneous across a coral reef ecosystem, with a shift from an oligotroph-dominated community (e.g. SAR11, Prochlorococcus, Synechococcus) in the open water and sandy substrate niches, to a community characterised by an increased frequency of copiotrophic bacteria (e.g. Vibrio, Pseudoalteromonas, Alteromonas) in the coral seawater niches. Among the major functional patterns observed were significant increases in genes associated with bacterial motility and chemotaxis in samples associated with the surfaces of coral colonies. These patterns were directly confirmed by chemotaxis experiments, which demonstrated that bacteria associated with the surfaces of the corals exhibited high levels of chemotaxis, particularly towards DMSP and several amino acids. Levels of chemotaxis by coral-associated bacteria were consistently higher than those demonstrated by non-coral associated bacteria. The phylogenetic composition of the chemotactic microbes, determined using 16S rRNA amplicon pyrosequencing, differed to the background community in the surrounding seawater, and incorporated several known coral-associated bacteria, Rhodobacteraceae, Flavobacteriaceae, Pseudomonadaceae and included potentially pathogenic Vibrios. Notably many of these bacteria, specifically Rhodobacterales, Flavobacterales and Vibrionales also became the dominant coral associated organisms under conditions of thermal stress experiments, indicating that these copiotrophic and chemotactic bacteria become key colonisers of thermally stressed corals.
Taken together our data demonstrate that coral reef bacterial communities are highly dynamic and that key groups of copiotrophic bacteria have the capacity to use sensitive chemotaxis to exploit nutrient gradients and potentially locate their coral hosts. Under conditions of heat stress, these behaviours may allow pathogenic organisms to locate and infect compromised hosts. 

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, May 29, 2013 - 18:15 - 18:30
Institution: 
Macquarie University
Title: 

Dissemination of antibiotic resistance determinants via sewage discharge from Davis Station, Antarctica

Abstract: 

Discharge of untreated or macerated sewage presents a significant risk to Antarctic marine ecosystems by introducing non-native microorganisms that potentially impact microbial communities and threaten health of Antarctic wildlife. Despite these risks, disposal of essentially untreated sewage continues in the Antarctic and sub-Antarctic. As part of an environmental impact assessment of the Davis Station, we investigated carriage of antibiotic resistance determinants in Escherichia coli isolates from marine water and sediments, marine invertebrates (Laturnula and Abatus), birds and mammals within 10 km of the Davis sewage outfall. Class 1 integrons typical of human pathogens and commensals were detected in 12% of E. coli isolates. E. coli carrying these integrons were primarily isolated from the near shore marine water column and the filter feeding mollusc Laturnula. Class 1 integrons were not detected in E. coli isolated from seal (Miroungaleonina, Leptonychotes weddellii) or penguin (Pygoscelis adeliae) feces. However, isolation of E. coli from these vertebrates’ faeces was also low. Consequently, sewage disposal is introducing non-native microorganisms and associated resistance genes into the Antarctic environment. The impact of this “gene pollution” on the diversity and evolution of native Antarctic microbial communities is unknown. 

 

Event Date: 
Wednesday, February 27, 2013 - 15:45 - 16:15
Institution: 
King Abdullah University of Science and Technology
Title: 

Microbial Ecology of the Red Sea

Abstract: 

The Red Sea is a harsh environment characterized by high temperatures, high salinity, high solar irradiation, and strong gradients from the North to the South. It also harbors at least 25 extreme environments at its seafloor, the deep-sea brine pools. These mostly anoxic brine pools are completely saturated with salt, and are among the most hostile habitats on earth. So far, studies on the microbiology of both, the water-column of the Red Sea and the deep-sea brine pools are scarce, mostly because of logistic and political reasons. King Abdullah University of Science and Technology (KAUST) is a new, international world-class research university in the Kingdom of Saudi Arabia that realizes the value of the Red Sea for the Middle East. The Marine Microbial Microbiology Group is part of the Red Sea Research Center at KAUST. In this presentation, I will summarize our holistic approach (community analyses, metagenomes, single-cell genomes, cultures) to a better understanding of the microbial communities of the Red Sea water-column and the brine pools, with a focus on adaptations of the major players to this peculiar environment.

Event Date: 
Wednesday, February 29, 2012 - 16:15 - 16:45
Institution: 
University of Saskatchewan, Canada
Title: 

The World’s Tipping Point: How genes, enzymes, microbes and plants regulate greenhouse gas release from Arctic Soils.

Abstract: 

Arctic soils contain as much carbon as the tropical rainforest. This carbon sequestered in permafrost is in danger of being released to the atmosphere. In this talk, I will discuss what regulates greenhouse gas release from Arctic soils and how, surprisingly, carbon containing greenhouse gases are not the key greenhouse gasses determining how warming Arctic soils influence our global climate. Drawing on the longest running climate change experiment in the Arctic, I will discuss how genes, enzymes, and microbial communities interact with one-another and with soil/plant properties to regulate greenhouse gas release at the field and continental scale. The role and importance of scale in determining biological interactions will be examined and what the implications of such scales are on our climate’s future.

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