Water masses' bacterial community structure and microbial activities in the Ross Sea, Antarctica

During the summer 2005/06, an oceanographic cruise was carried out in the Ross Sea, from CapeAdare, through the Terra Nova Bay polynya to the eastern edge of the Ross Ice Shelf. We analysed microbialactivities (prokaryotic carbon production, protease, phosphatase, beta-glucosidase and lipase activity) andbacterial community structure (using Denaturing Gradient Gel Electrophoresis - DGGE) in order to establish ifdifferences in bacterioplankton assemblages and their metabolic requirements occur within the five Ross Seawater masses: Antarctic Surface Waters (AASW), High Salinity Shelf Water (HSSW), Ice Shelf Water (ISW),Antarctic Bottom Water (AABW), Circumpolar Deep Water (CDW). Differences in activities were foundbetween the highly active AASW and all the other water bodies. A Principal Component Analysis highlightedtwo main gradients: in the Cape Adare area (AASWn, CDW and AABW) higher phosphatase, lipase andglycolytic activities, increasing towards the surface, were identified, whereas in the southern sector of the basin[AASWs and (m)HSSW] higher leucine uptake and polypeptide degradation characterized the second gradient.DGGE fingerprinting showed for the first time that different water masses harboured diverse bacterialcommunities, highlighting the high specificity of deep water assemblages. Alpha- and Gammaproteobacteriarepresented the main phylogenetic groupings in all samples and no substantial difference in the phylogeneticcomposition of assemblages was found between different water masses.