Project description:Ammonia-oxidizing archaea (AOA) have been reported at high abundance in much of the global ocean, even in environments such as pelagic oxygen minimum zones (OMZs), where conditions seem unlikely to support aerobic ammonium oxidation. Due to the lack of information on any potential alternative metabolism of AOA, the AOA community composition might be expected to differ between oxic and anoxic environments, indicating some difference in ecology and/or physiology of the AOA assemblage. This hypothesis was tested by evaluating AOA community composition using a functional gene microarray that targets the ammonia monooxygenase gene subunit A (amoA). The relationship between environmental parameters and the biogeography of the Arabian Sea and the Eastern Tropical South Pacific (ETSP) AOA assemblages was investigated using principal component analysis (PCA) and redundancy analysis (RDA). In both the Arabian Sea and the ETSP, AOA communities within the core of the OMZ were not significantly different from those inhabiting the oxygenated surface waters above the OMZ. The AOA communities in the Arabian Sea were significantly different from those in the ETSP. In both oceans, the abundance of archaeal amoA gene in the core of the OMZ was higher than that in the surface waters. Our results indicate that AOA communities are distinguished by their geographic origin. RDA suggested that temperature was the main factor that correlated with the differences between the AOA communities from the Arabian Sea and those from the ETSP. Physicochemical properties that characterized the different environments of the OMZ and surface waters played a less important role than did geography in shaping the AOA community composition.
Project description:Seamounts, often rising hundreds of metres above the surrounding seafloor, obstruct the flow of deep-ocean water. While the resultant entrainment of deep-water by seamounts is predicted from ocean circulation models, its empirical validation has been hampered by the large scale and slow rate of the interaction. To overcome these limitations we use the growth of planktonic bacteria to assess the interaction rate. The selected study site, Tropic Seamount, in the North-Eastern Atlantic represents the majority of isolated seamounts, which do not affect the surface ocean waters. We prove deep-water is entrained by the seamount by measuring 2.3 times higher bacterial concentrations in the seamount-associated or ‘sheath’ water than in deep-ocean water unaffected by seamounts. Genomic analyses of the dominant sheath-water bacteria confirm their planktonic origin, whilst proteomic analyses indicate their slow growth. According to our radiotracer experiments, the doubling time of sheath-water bacterioplankton is 1.5 years. Therefore, for bacterioplankton concentration to reach 2.3 times higher in the ambient seawater, the seamount would need to retain deep-ocean water for more than 3.5 years. We propose that turbulent mixing of the retained sheath-water could stimulate bacterioplankton growth by increasing the cell encounter rate with the ambient dissolved organic molecules. If some of these molecules chelate hydroxides of iron and manganese, bacterioplankton consumption of the organic chelators would result in precipitation of insoluble hydroxides. Hence precipitated hydroxides would form ferromanganese deposits as a result of the bacterioplankton-mediated deep-water seamount interaction.
Project description:Ammonia-oxidizing archaea (AOA) have been reported at high abundance in much of the global ocean, even in environments such as pelagic oxygen minimum zones (OMZs), where conditions seem unlikely to support aerobic ammonium oxidation. Due to the lack of information on any potential alternative metabolism of AOA, the AOA community composition might be expected to differ between oxic and anoxic environments, indicating some difference in ecology and/or physiology of the AOA assemblage. This hypothesis was tested by evaluating AOA community composition using a functional gene microarray that targets the ammonia monooxygenase gene subunit A (amoA). The relationship between environmental parameters and the biogeography of the Arabian Sea and the Eastern Tropical South Pacific (ETSP) AOA assemblages was investigated using principal component analysis (PCA) and redundancy analysis (RDA). In both the Arabian Sea and the ETSP, AOA communities within the core of the OMZ were not significantly different from those inhabiting the oxygenated surface waters above the OMZ. The AOA communities in the Arabian Sea were significantly different from those in the ETSP. In both oceans, the abundance of archaeal amoA gene in the core of the OMZ was higher than that in the surface waters. Our results indicate that AOA communities are distinguished by their geographic origin. RDA suggested that temperature was the main factor that correlated with the differences between the AOA communities from the Arabian Sea and those from the ETSP. Physicochemical properties that characterized the different environments of the OMZ and surface waters played a less important role than did geography in shaping the AOA community composition. 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:Iron-sulfur minerals such as pyrite are found in many marine benthic habitats. At deep-sea hydrothermal vent sites they occur as massive sulfide chimneys. Hydrothermal chimneys formed by mineral precipitation from reduced vent fluids upon mixing with cold oxygenated sea water. While microorganisms inhabiting actively venting chimneys and utilizing reduced compounds dissolved in the fluids for energy generation are well studied, only little is known about the microorganisms inhabiting inactive sulfide chimneys. We performed a comprehensive meta-proteogenomic analysis combined with radiometric dating to investigate the diversity and function of microbial communities found on inactive sulfide chimneys of different ages from the Manus Basin (SW Pacific). Our study sheds light on potential lifestyles and ecological niches of yet poorly described bacterial clades dominating inactive chimney communities.