Planktology

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, April 29, 2015 - 19:00 - 19:45
Institution: 
University of Southern California
Title: 

Bridging the gap between functional genes and biogeochemistry: a DMSP case study

Abstract: 

A large fraction of the surface ocean food web is active in producing and cycling both dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS).  In addition to the potential climatic significance of DMS production, the role that these compounds play in mediating ecosystem dynamics remains unknown.  An interdisciplinary dataset of biological, chemical and physical measurements was used to test current hypotheses of the role of light and carbon supply in regulating upper-ocean sulfur cycling in oligotrophic regions. Our results suggest that UV-A radiation dose plays an important role in both phytoplankton DMS production and bacterial DMSP degradation. We suggest a modified ‘bacterial switch’ hypothesis where the prevalence of different bacterial DMSP degradation pathways is regulated by a complex set of factors including carbon supply, temperature, and UV-A dose. Finally, numerical models of varying complexity were used to link genetic and enzyme data to biogeochemical rates.

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, 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, October 26, 2011 - 18:00 - 18:15
Institution: 
Macquarie University
Title: 

Marine Synechococcus: genomics, genetics and ecology of a ubiquitous primary producer

Abstract: 

Although life in the oceans presents some of the most amazing and colourful spectacles, from whales to tropical reefs, the molecular age has led us to a deeper understanding of the diversity and activity of the microorganisms that have a profound influence on our climate. Up until the late 1970s the smallest and most abundant phytoplankton in the oceans had remained undiscovered. These organisms have since been characterised as Synechococcus and Prochlorococcus which are responsible for 2/3 of all marine CO2 fixation. For more than a decade we have been exploring the molecular ecology, physiology, and genomes of these prokaryotic primary producers. Molecular approaches have led to an understanding that genome diversity and plasticity underpin their global distribution and lead us to a pathway from genes, the fundamental units of selection, to a better understanding of the activity of microorganisms that drive geochemical cycles.

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