Synechococcus

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, February 25, 2015 - 17:00 - 17:30
Institution: 
University of Southern Maine
Title: 

Prochlorococcus: the “invisible forest” in the ocean’s Outback.

Abstract: 

The smallest, most abundant phototroph in the world, Prochlorococcus, dominates the base of the food web in the “Outback” of the world’s oceans, the nutrient-depleted ocean gyres. This unicellular, marine cyanobacterium, unknown only 30 years ago, is an oligotrophic specialist with a streamlined genome and reduced cellular requirement for the limited resources available in this environment. Based on physiological and molecular analyses of isolated strains from different oceans and depths, two broad groupings of Prochlorococcus were characterized: high- and low-light adapted “ecotypes”. Within these broad groupings are many subclades, some of which have been shown to dominate under certain temperature and light conditions. Through additional culture-based studies, my lab has been exploring nutrient physiology and other physiological characteristics that may contribute to the ecology and evolution of other Prochlorococcus subgroups. Some subgroups have the capacity to utilize nitrate, which was not the case for the initial isolates of Prochlorococcus, and others differ in their pigmentation. We have also found that Prochlorococcus regulates its uptake velocity and specific affinity for inorganic and organic phosphorus under P stress conditions. Examining the physiology, ecology and genomics of Prochlorococcus isolates and natural populations is providing insights into how these tiny photosynthesizing cells create a stable, yet invisible forest in the deserts of the world’s oceans.

Event Date: 
Wednesday, July 30, 2014 - 18:15 - 18:30
Institution: 
Macquarie University
Title: 

Effect of Low Temperature on Tropical and Temperate Isolates of Marine Synechococcus.

Abstract: 

An abundant and globally occurring marine picocyanobacterium, the genus Synechococcus is an important player in oceanic primary production and global carbon cycling. In the complex marine environment, this widespread organism has evolved to successfully colonize and inhabit different environmental niches. Their biogeographic distribution suggests that Synechococcus ecotypes exhibit thermal niche preferences. Temperature is a key environmental variable and the elucidation of the temperature stress acclimation in members of this genus can shed light on the molecular mechanisms involved in their adaptive capability. The growth of four representative Synechococcus isolates of various ecotypes from tropical and temperate regions were monitored under various temperature conditions. This revealed drastic differences in growth rates in correlation with their thermal niche preferences. The temperate strains CC9311 and BL107 displayed higher growth rates at lower temperatures while tropical strains WH8102 and WH8109 grew better at higher temperatures. In order to further elucidate their thermal niche preference, the molecular factors influencing the temperature-related growth patterns were explored through global proteomic analysis of WH8102 and BL107. Whole cell lysates of the strains grown at different temperature conditions were fractionated using 1D SDS-PAGE and analysed using label-free quantitative proteomics. Protein identifications provided 27% and 40% coverage of the whole genome for WH8102 and BL107, respectively. Quantitation of protein expression revealed 22% and 20% of the identified proteins were differentially expressed in WH8102 and BL107, respectively. The results were further investigated using qRT-PCR and PAM fluorometry. Differential expression revealed that low temperature appeared to have a significant effect on the photosynthetic machinery. The light harvesting components, phycobilisomes exhibited a reduced expression which could be the result of protein degradation due to photo-oxidative damage and/or as a mechanism to restore the energy balance disturbed as a consequence of low temperature. The lowered phycobilisome expression is found to be a common low temperature-related response between the tropical and temperate isolates. Within the photosynthetic reaction centres, differences in the expression of some core proteins were observed between the two isolates. The expression of core proteins could correlate with the efficiency of repair mechanisms involved in the replacement of photo-damaged core proteins. This differential expression sheds light on the underlying factors which potentially influence the differences in the thermal ranges of tropical and temperate isolates.

Many scientific minds gathered together for a series of talks on a warm October evening at the Australian Museum.

The first presenter, Martin Ostrowski from Macquarie University continued from last month’s marine microbiology theme by presenting the genetics and ecology of Synechococcus. He demonstrated the distribution patterns of Synechococcus lineages are similar in different ocean systems with comparable environmental conditions. However, specific Synechococcus lineages show a distinct distribution pattern at a global scale. This finding may be useful to predict bacterial community structures in marine ecosystems.

A keen crowd of about 35 braved the rain to attend the September JAMS, which this month was held within the more spacious setting of the 4th floor at the Australian Museum. This month’s presentations all had a marine flavour, with the audience enjoying three entertaining talks focussed on the community dynamics and biogeochemical capabilities of marine microorganisms.

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.

Event Date: 
Wednesday, September 28, 2011 - 18:15 - 18:30
Institution: 
University of New South Wales
Title: 

The Polar Front is a major boundary in Southern Ocean picoplanktonic biogeography.

Abstract: 

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.

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