The Polar Front is a major boundary in Southern Ocean picoplanktonic biogeography.
The Polar Frontal Zone, at around 60 S, is the boundary in the SO between the cold Antarctic Zone to its south and the warmer Subantarctic Zone to the north. It is defined at its southern extent by the Polar Front (PF) and its northern by the Subantarctic Front. Across each of these fronts, the temperature decreases southward in a stepwise fashion (e.g. 1.5-2C over a distance of 30-50 km), accompanied by changes in salinity and density. In this study we performed a high-throughput metagenomic survey of Southern Ocean picoplankton during the austral summer of 2007-2008 and found that the PF was a major biogeographical boundary, separating microbial assemblages with distinct taxonomic and functional profiles. None of the physiochemical parameters measured were correlated with taxonomic or functional profile. However, we observed a strong over-representation of the oligotrophic SAR11 and SAR116 clades, the cyanobacterial genera Prochlorococcus and Synechococcus and Roseobacter spp. north of the PF. Conversely, a high abundance of the uncultured chemolithoautotrophic SUP05 clade and of ammonia oxidising archaea characterised waters south of the PF. This and other evidence suggests that mixing between deep and shallow waters shapes bacterial communities south of the PF.
Microarrays within the environmental microbiology toolbox.
Microbial communities are large and complex, to an extent often challenging human apprehension. An intrinsic challenge of microbial ecology is to assay this complexity in a way that promotes understanding. Every molecular method applied in microbial ecology has advantages and disadvantages, and it is an important task to make the best compromise between these methods in light of the experimental questions raised. Microarrays enable a reasonably high throughput in terms of sample number while providing a fairly high resolution of detected taxa, genes or gene variants. This combination makes microarrays often an optimal compromise between throughput and resolution in microbial ecology. The talk will describe the development and validation of a novel amoA microarray, followed by selected tales from nitrifier and methanotroph ecology studies illustrating the potential and limitations of microarray technology in microbial ecology.
Bacterial community assembly based on functional genes rather than species.
principles underlying the assembly and structure of complex microbial
communities are an issue of long-standing concern to the field of microbial
ecology. We analyzed the community membership of bacterial communities
associated with the green macroalga Ulva
australis, and proposed a competitive lottery model for colonization of the
algal surface in an attempt to explain the surprising lack of similarity in
species composition across different algal samples. We then investigated the
link between community structure and function in these communities, using
metagenomic sequence analysis. Despite the high phylogenetic variability in
microbial species composition on different U.
australis (only 15% similarity between samples), similarity in functional
composition was high (70%), and a core of functional genes present across all
algal-associated communities was identified that were consistent with the
ecology of surface- and host associated bacteria. These functions were
distributed widely across a variety of taxa or phylogenetic groups. This
observation of similarity in habitat (niche) use with respect to functional
genes, but not species, together with the relative ease with which bacteria
share genetic material, suggests that the key level at which to address the
assembly and structure of bacterial communities may not be “species” (by means
of rRNA taxonomy), but rather the more functional level of genes.
Sizing up the symbiotic partnership: towards a single-cell view of nutrients uptake in cnidaria-dinoflagellate symbiosis
Reefs based on scleractinian corals are among the most productive and biologically diverse ecosystems on Earth. At the heart of their success as the architects of coral reefs, is their symbiosis with dinoflagellate algae, which live within their tissues and provide corals with an enlarged metabolic repertoire. Thus corals are ‘polytrophic’, being able to acquire carbon-based nutrients from sunlight through their algal symbionts (‘autotrophic’), feeding on plankton (‘heterotrophic’), and absorbing dissolved nutrients from the surrounding water. These strategies increase the nutritional options of corals in an environment where planktonic food supplies and dissolved nutrients in seawater may be episodic.
The intertwined nature of coral-dinoflagellate endosymbiosis has made the relative quantification of host and symbiont contributions to metabolic activities extremely difficult so far. Consequently, whilst we now recognize the threats of human activity, future climate change and associated symptoms of stress on the reef, very little is known about the nutritional function of the cnidarian-dinoflagellate symbiosis that underpins and maintains reef health.
In this talk, I will explore how the development of new technologies combining isotopic labeling and high resolution imaging analysis opens a new interdisciplinary frontier in the study of such symbiotic interactions with direct implications for how these organisms will respond to environmental changes.
The Effects of Environmental Temperature on Biogeographic Boundaries in SAR11 Marine Bacteria.
The ubiquitous SAR11 bacterial clade is the most abundant type of organism in the world's oceans, but the reasons for its success are not fully elucidated. We provide the first global characterisation of the distribution of this marine heterotrophic bacterium, from waters spanning temperatures -2ºC to 30ºC. Our data show a stable co-occurrence of paired ecotypes within both "tropical" (>20ºC) and "polar" (<10ºC) biomes, highlighting ecological niche differentiation between the major SAR11 lineages. All ecotypes display transitions in abundance that are strongly correlated to temperature. Our data demonstrates the importance of adaptive radiation in the organism's ability to proliferate throughout the world's oceans. Based on projections of sea surface temperature in 2090 we predict a redistribution of SAR11 ecotypes within a significant proportion of the ocean realm as a result of global warming.
Marine Synechococcus: genomics, genetics and ecology of a ubiquitous primary producer
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.
An enthusiastic crowd of around 50 gathered to see out the winter months on the last day of August at another great JAMS meeting at the Australian Museum. The JAMS series brings together research microbiologists, including post-docs, PhD students and senior researchers, working in non-clinical projects from institutes throughout the Sydney region. The JAMS organisers would like to thank the Australian Museum for providing the fantastic venue for the meetings, as well as the Australian Society for Microbiology for sponsoring the event to provide pizza and drinks.
It's true, the first "pilot" meeting of JAMS was almost a year ago on november 24th 2010.Not long before (to me it feels like yesterday), Andy, Ian, Mike and myself met at the Trinity bar and started tossing around ideas on getting it all started. We still had no clue of when, where, or how we were going to do it. We just knew it had to be done and we'd all benefit from it.We have come a long way from there. We've had 29 speakers, some from overseas, many from out of town giving great seminars. We've had talks ranging from viruses to mosquitoes, from tropical oceans to alpine soils. But above all, we've had lots of fun!So to celebrate JAMS's first year of success I think we should have some sort of a birthday celebration.