Vertical, seasonal and geographical patterns in ocean microbial communities have been observed in many studies, but the resolution of community dynamics has been limited by the scope of data sets, which are seldom up to the task of illuminating the highly structured and rhythmic patterns of change found in ocean ecosystems. We studied vertical and temporal patterns in the microbial community composition in a set of 412 samples collected from the upper 300 m of the water column in the northwestern Sargasso Sea, on cruises between 1991 and 2004. The region sampled spans the extent of deep winter mixing and the transition between the euphotic and the upper mesopelagic zones, where most carbon fixation and reoxidation occurs. A bioinformatic pipeline was developed to de-noise, normalize and align terminal restriction fragment length polymorphism (T-RFLP) data from three restriction enzymes and link T-RFLP peaks to microbial clades. Non-metric multidimensional scaling statistics resolved three microbial communities with distinctive composition during seasonal stratification: a surface community in the region of lowest nutrients, a deep chlorophyll maximum community and an upper mesopelagic community. A fourth microbial community was associated with annual spring blooms of eukaryotic phytoplankton that occur in the northwestern Sargasso Sea as a consequence of winter convective mixing that entrains nutrients to the surface. Many bacterial clades bloomed in seasonal patterns that shifted with the progression of stratification. These richly detailed patterns of community change suggest that highly specialized adaptations and interactions govern the success of microbial populations in the oligotrophic ocean.

Marine dissolved organic matter (DOM) is one of the most heterogeneous and largest pools of reactive carbon on earth, rivaling in mass the carbon in atmospheric carbon dioxide. Nevertheless, the molecular-level composition of marine DOM has eluded detailed description, impeding inquiry into the specific mechanisms that add or remove compounds from the DOM pool. Here we describe the molecular-level composition of C 18 -extracted DOM along an eastwest transect of the North Atlantic Ocean. We examine the changes in DOM composition along this transect with ultrahigh resolution mass spectrometry and multivariate statistics. We use indicator species analysis (ISA) to identify possible source markers for photochemical

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The nucleocapsid (N) proteins of hantaviruses such as the Sin Nombre virus (SNV) bind to membranes and viral RNAs, associate with transcription and replication complexes, and oligomerize during the process of virus assembly. N proteins trimerize in vitro and in vivo, and associate via assembly domains at their amino-and carboxyl-terminal ends. Because structure prediction algorithms suggested that N protein residues 3-75 form two coiled-coil motifs separated by an intervening kink or turn sequence, we examined the properties of peptides representing SNV N protein residues 3-35, 43-75, and 3-75. Of the three peptides, N-(3-35) assembled coiledcoil oligomers only at high concentration and low temperature. In contrast, N-(43-75) efficiently trimerized at low concentration, implying that it carries a coiled-coil trigger sequence. Interestingly, while the longer peptide, N-(3-75), assembled dimers and/or trimers at high concentration, at low concentration it appeared to adopt an intramolecular helix-turn-helix conformation. These results suggest that N protein oligomerization involves the bundling of intramolecular antiparallel coils or a conformational switch from intra-to intermolecular coiled-coils.Hantaviruses are enveloped, animal viruses that can be lethal to humans as a consequence of virus-induced heart, lung, and kidney damage (1, 2). Hantaviral genomes consist of three negative-sense RNAs, which encode the viral RNA-dependent RNA polymerase (RdRp), glycoproteins, and nucleocapsid (N) 1 protein (1, 2). The N proteins associate with viral membranes, encapsidate viral RNAs, form viral core structures, and probably participate in viral transcription and replication processes (1, 2).Although hantavirus N protein sequences are well conserved and are homologous to the nucleocapsid proteins of other bunyaviruses (1-3), relatively little is known about the structure or functional domains of the 420 -430-residue hantaviral N proteins. Recent studies have mapped RNA and membrane binding domains to the central and carboxyl-terminal sequences of the protein, respectively (4 -7). Additionally, we have demonstrated that N protein trimers can be detected in virus particles, in infected cells, and in vitro (8), suggesting that trimers represent natural, functional nucleocapsid protein oligomers. Using a genetic assay for the analysis of protein-protein contacts, we have mapped the association domains of the Sin Nombre hantavirus (SNV; Ref.3) nucleocapsid protein to its carboxyl-terminal half and its amino terminus (8).The identification of the SNV N protein amino terminus (sequence shown in Fig. 1) as an interaction domain is of interest because structure prediction algorithms implicate this region as a coiled-coil motif (8, 10). In particular, examination of N protein sequences from seven different hantavirus strains suggested that the amino-terminal 35 residues form trimeric coiled-coils, while residues 40 -75 were predicted to form either dimeric or trimeric coiled-coils (8, 10). To test these structure predictions and t...