Project description:As an essential micronutrient that is scarce in surface ocean waters, zinc (Zn) has the potential to limit oceanic photosynthetic productivity and influence the global carbon cycle. Here we observed Zn co-limitation with iron (Fe) in the natural phytoplankton community of Terra Nova Bay, Antarctica, induced by the drawdown of seawater CO2 and dZn during a bloom. Incubations amended with Zn resulted in significantly higher chlorophyll a content and greater macronutrient and dissolved inorganic carbon drawdown compared to Fe addition alone. Multiple Zn and Fe response proteins were observed in experimental and water column samples demonstrating co-stress in various algal taxa. Together these results demonstrate that Zn limitation can occur in productive Antarctic coastal ecosystems. Thus, Zn may be an important factor limiting the total productivity potential of marine phytoplankton.
Project description:The abundance of bacterial (AOB) and archaeal (AOA) ammonia oxidisers, assessed using quantitative PCR measurements of their respective a-subunit of the ammonia monooxygenase (amoA) genes, and ammonia oxidation rates were measured in four contrasting coastal sediments in the Western English Channel. Sediment was sampled bimonthly from July 2008 to May 2011, and measurements of ammonia oxidiser abundance and activity compared to a range of environmental variables including salinity, temperature, water column nutrients and sediment carbon and nitrogen content. Despite a higher abundance of AOA amoA genes within all sediments, and at all time-points, rates of ammonia oxidation correlated with AOB and not AOA amoA gene abundance. Other than ammonia oxidation rate, sediment particle size was the only variable that correlated with the spatial and temporal patterns of AOB amoA gene abundance, implying a preference of the AOB for larger sediment particles. This is possibly due to deeper oxygen penetration into the sandier sediments, increasing the area available for ammonia oxidation to occur, higher concentrations of inhibitory sulphide with pore waters of muddier sediments or a combination of both oxygen and sulphide concentrations. Similar to many other temporal studies of nitrification within estuarine and coastal sediments, decreases in AOB amoA gene abundance were evident during summer and autumn, with maximum abundance and ammonia oxidation rates occurring in winter and early spring. The lack of correlation between AOA amoA gene abundance and ammonium oxidation rate suggests an alternative role for amoA-carrying AOA within these sediments.
Project description:The abundance of bacterial (AOB) and archaeal (AOA) ammonia oxidisers, assessed using quantitative PCR measurements of their respective a-subunit of the ammonia monooxygenase (amoA) genes, and ammonia oxidation rates were measured in four contrasting coastal sediments in the Western English Channel. Sediment was sampled bimonthly from July 2008 to May 2011, and measurements of ammonia oxidiser abundance and activity compared to a range of environmental variables including salinity, temperature, water column nutrients and sediment carbon and nitrogen content. Despite a higher abundance of AOA amoA genes within all sediments, and at all time-points, rates of ammonia oxidation correlated with AOB and not AOA amoA gene abundance. Other than ammonia oxidation rate, sediment particle size was the only variable that correlated with the spatial and temporal patterns of AOB amoA gene abundance, implying a preference of the AOB for larger sediment particles. This is possibly due to deeper oxygen penetration into the sandier sediments, increasing the area available for ammonia oxidation to occur, higher concentrations of inhibitory sulphide with pore waters of muddier sediments or a combination of both oxygen and sulphide concentrations. Similar to many other temporal studies of nitrification within estuarine and coastal sediments, decreases in AOB amoA gene abundance were evident during summer and autumn, with maximum abundance and ammonia oxidation rates occurring in winter and early spring. The lack of correlation between AOA amoA gene abundance and ammonium oxidation rate suggests an alternative role for amoAÂ-carrying AOA within these sediments. Two color array (Cy3 and Cy5): the universal standard 20-mer oligo is printed to the slide with a 70-mer oligo (an archetype). Environmental DNA sequences (fluoresced with Cy3) within 15% of the 70-mer conjugated to a 20-mer oligo (fluoresced with Cy5) complementary to the universal standard will bind to the oligo probes on the array. Signal is the ratio of Cy3 to Cy5. Three replicate probes were printed for each archetype. Two replicate arrays were run on duplicate targets.
Project description:Deep Lake is a hypersaline system in Antarctica (68°33’36.8S, 78°11’48.7E) that is so saline it remains liquid at –20°C (DeMaere et al 2013). The lake is dominated by haloarchaea, comprising a low-complexity community that differs greatly to warm-hot latitude hypersaline systems, is hierarchical structured, and supports a high level of intergenera gene exchange. Metaproteomics was performed on biomass that was collected in the austral summer of 2008 by sequential size fractionation (20 – 3 µm, 3 – 0.8 µm, 0.8 – 0.1 µm). The data were integrated to obtain a systems level view of the active host-virus interactions occurring in this novel aquatic Antarctic system. DeMaere MZ, Williams TJ, Allen MA, Brown MV, Gibson JA, Rich J, Lauro FM, Dyall-Smith M, Davenport KW, Woyke T, Kyrpides NC, Tringe SG, Cavicchioli R (2013) High level of intergenera gene exchange shapes the evolution of haloarchaea in an isolated Antarctic lake. Proc Natl Acad Sci USA 110: 16939-16944
Project description:Understanding the environmental factors that shape microbial communities is crucial, especially in extreme environments, like Antarctica. Two main forces were reported to influence Antarctic soil microbes: birds and plants. Both birds and plants are currently undergoing unprecedented changes in their distribution and abundance due to global warming. However, we need to clearly understand the relationship between plants, birds and soil microorganisms. We therefore collected rhizosphere and bulk soils from six different sampling sites subjected to different levels of bird influence and colonized by Colobanthus quitensis and Deschampsia antarctica in the Admiralty Bay, King George Island, Maritime Antarctic. Microarray and qPCR assays targeting 16S rRNA genes of specific taxa were used to assess microbial community structure, composition and abundance and analyzed with a range of soil physico-chemical parameters. The results indicated significant rhizosphere effects in four out of the six sites, including areas with different levels of bird influence. Acidobacteria were significantly more abundant in soils with little bird influence (low nitrogen) and in bulk soil. In contrast, Actinobacteria were significantly more abundant in the rhizosphere of both plant species. At two of the sampling sites under strong bird influence (penguin colonies), Firmicutes were significantly more abundant in D. antarctica rhizosphere but not in C. quitensis rhizosphere. The Firmicutes were also positively and significantly correlated to the nitrogen concentrations in the soil. We conclude that the microbial communities in Antarctic soils are driven both by bird and plants, and that the effect is taxa-specific.