Bajic Vladimir B.

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Bajic
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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
    Toward an understanding of the molecular mechanisms of barnacle larval settlement : a comparative transcriptomic approach
    (Public Library of Science, 2011-07-29) Chen, Zhang-Fan ; Matsumura, Kiyotaka ; Wang, Hao ; Arellano, Shawn M. ; Yan, Xingcheng ; Alam, Intikhab ; Archer, John A. C. ; Bajic, Vladimir B. ; Qian, Pei-Yuan
    The barnacle Balanus amphitrite is a globally distributed biofouler and a model species in intertidal ecology and larval settlement studies. However, a lack of genomic information has hindered the comprehensive elucidation of the molecular mechanisms coordinating its larval settlement. The pyrosequencing-based transcriptomic approach is thought to be useful to identify key molecular changes during larval settlement. Using 454 pyrosequencing, we collected totally 630,845 reads including 215,308 from the larval stages and 415,537 from the adults; 23,451 contigs were generated while 77,785 remained as singletons. We annotated 31,720 of the 92,322 predicted open reading frames, which matched hits in the NCBI NR database, and identified 7,954 putative genes that were differentially expressed between the larval and adult stages. Of these, several genes were further characterized with quantitative real-time PCR and in situ hybridization, revealing some key findings: 1) vitellogenin was uniquely expressed in late nauplius stage, suggesting it may be an energy source for the subsequent non-feeding cyprid stage; 2) the locations of mannose receptors suggested they may be involved in the sensory system of cyprids; 3) 20 kDa-cement protein homologues were expressed in the cyprid cement gland and probably function during attachment; and 4) receptor tyrosine kinases were expressed higher in cyprid stage and may be involved in signal perception during larval settlement. Our results provide not only the basis of several new hypotheses about gene functions during larval settlement, but also the availability of this large transcriptome dataset in B. amphitrite for further exploration of larval settlement and developmental pathways in this important marine species.
  • 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.