Oligotroph

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, 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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