Bajic Vladimir B.

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Vladimir B.

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  • Article
    Unique prokaryotic consortia in geochemically distinct sediments from Red Sea Atlantis II and Discovery Deep brine pools
    (Public Library of Science, 2012-08-20) Siam, Rania ; Mustafa, Ghada A. ; Sharaf, Hazem ; Moustafa, Ahmed ; Ramadan, Adham R. ; Antunes, Andre ; Bajic, Vladimir B. ; Stingl, Uli ; Marsis, Nardine G. R. ; Coolen, Marco J. L. ; Sogin, Mitchell L. ; Ferreira, Ari J. S. ; El Dorry, Hamza
    The seafloor is a unique environment, which allows insights into how geochemical processes affect the diversity of biological life. Among its diverse ecosystems are deep-sea brine pools - water bodies characterized by a unique combination of extreme conditions. The ‘polyextremophiles’ that constitute the microbial assemblage of these deep hot brines have not been comprehensively studied. We report a comparative taxonomic analysis of the prokaryotic communities of the sediments directly below the Red Sea brine pools, namely, Atlantis II, Discovery, Chain Deep, and an adjacent brine-influenced site. Analyses of sediment samples and high-throughput pyrosequencing of PCR-amplified environmental 16S ribosomal RNA genes (16S rDNA) revealed that one sulfur (S)-rich Atlantis II and one nitrogen (N)-rich Discovery Deep section contained distinct microbial populations that differed from those found in the other sediment samples examined. Proteobacteria, Actinobacteria, Cyanobacteria, Deferribacteres, and Euryarchaeota were the most abundant bacterial and archaeal phyla in both the S- and N-rich sections. Relative abundance-based hierarchical clustering of the 16S rDNA pyrotags assigned to major taxonomic groups allowed us to categorize the archaeal and bacterial communities into three major and distinct groups; group I was unique to the S-rich Atlantis II section (ATII-1), group II was characteristic for the N-rich Discovery sample (DD-1), and group III reflected the composition of the remaining sediments. Many of the groups detected in the S-rich Atlantis II section are likely to play a dominant role in the cycling of methane and sulfur due to their phylogenetic affiliations with bacteria and archaea involved in anaerobic methane oxidation and sulfate reduction.
  • Article
    Core microbial functional activities in ocean environments revealed by global metagenomic profiling analyses
    (Public Library of Science, 2014-06-12) Ferreira, Ari J. S. ; Siam, Rania ; Setubal, Joao C. ; Moustafa, Ahmed ; Sayed, Ahmed ; Chambergo, Felipe S. ; Dawe, Adam S. ; Ghazy, Mohamed A. ; Sharaf, Hazem ; Ouf, Amged ; Alam, Intikhab ; Abdel-Haleem, Alyaa M. ; Lehvaslaiho, Heikki ; Ramadan, Eman ; Antunes, Andre ; Stingl, Ulrich ; Archer, John A. C. ; Jankovic, Boris R. ; Sogin, Mitchell L. ; Bajic, Vladimir B. ; El-Dorry, Hamza
    Metagenomics-based functional profiling analysis is an effective means of gaining deeper insight into the composition of marine microbial populations and developing a better understanding of the interplay between the functional genome content of microbial communities and abiotic factors. Here we present a comprehensive analysis of 24 datasets covering surface and depth-related environments at 11 sites around the world's oceans. The complete datasets comprises approximately 12 million sequences, totaling 5,358 Mb. Based on profiling patterns of Clusters of Orthologous Groups (COGs) of proteins, a core set of reference photic and aphotic depth-related COGs, and a collection of COGs that are associated with extreme oxygen limitation were defined. Their inferred functions were utilized as indicators to characterize the distribution of light- and oxygen-related biological activities in marine environments. The results reveal that, while light level in the water column is a major determinant of phenotypic adaptation in marine microorganisms, oxygen concentration in the aphotic zone has a significant impact only in extremely hypoxic waters. Phylogenetic profiling of the reference photic/aphotic gene sets revealed a greater variety of source organisms in the aphotic zone, although the majority of individual photic and aphotic depth-related COGs are assigned to the same taxa across the different sites. This increase in phylogenetic and functional diversity of the core aphotic related COGs most probably reflects selection for the utilization of a broad range of alternate energy sources in the absence of light.