88,747 research outputs found
Atomic force microscopy reveals microscale networks and possible symbioses among pelagic marine bacteria
No full textMarine Bacteria and Archaea ('bacteria') interact with upper ocean productivity to fundamentally influence its biogeochemical fate with consequences for ecosystems and global climate. Most bacteria-mediated carbon cycling is due to numerically dominant free-living bacteria, but their adaptive strategies to interact with primary productivity are not fully understood. Using atomic force microscopy (AFM), we made the surprising discovery that a substantial, and variable, fraction (on average 30 +/- 17.8% with a range of 0 to 55%) of 'free-living' bacteria in our samples from California coastal and open ocean environments were, in fact, intimately associated with other bacteria at nanometer to micrometer scales. Twenty-one to 43% of bacteria, including Synechococcus, were conjoint. Such close associations could indicate symbioses; however, they could also be antagonistic, parasitic, neutral, or accidental. Further, a substantial fraction (4 to 55%) of bacteria was connected by pili and gels into cell-cell pairs or occurred in networks of up to 20 cells. We frequently observed nanoparticles associated with the networks, raising the question of their identity and origin (e.g. scavenged from the seawater colloid pool by the networks or produced by the bacteria within the networks). The networks occasionally contained structures that morphologically resembled coccoliths or protist scales. These may impart ballast to sinking particles if the networks coalesce to form larger, sinking, particles. Our finding of abundant bacteria-bacteria associations and possible microenvironment structuring by pelagic bacteria offers a novel context for bacterial ecology and diversity and models of ocean productivity and elemental cycling
Microbial structuring of marine ecosystems
No full textDespite the impressive advances that have been made in assessing the diversity of marine microorganisms, the mechanisms that underlie the participation of microorganisms in marine food webs and biogeochemical cycles are poorly understood. Here, we stress the need to examine the biochemical interactions of microorganisms with ocean systems at the nanometre to millimetre scale - a scale that is relevant to microbial activities. The local impact of microorganisms on biogeochemical cycles must then be scaled up to make useful predictions of how marine ecosystems in the whole ocean might respond to global change. This approach to microbial oceanography is not only helpful, but is in fact indispensable
A new class of transparent organic particles in seawater visualized by a novel fluorescence approach
No full textA method for visualizing transparent material in seawater, described here, has led to the discovery of novel particles. The protocol is based on Alcian Blue and SYBR Gold staining of seawater samples on polycarbonate filters. While the particles detected by our method may have some overlap with previously described transparent exopolymer particles and Coomassie stained particles, these particles largely comprise a previously undetected class. We propose that the particles are detected because they cause spatially explicit inhibition of Alcian Blue quenching of SYBR Cold fluorescence of the filter. Samples collected from various locations (Ellen Browning Scripps Memorial Pier, California, the Palmer Peninsula, Antarctica, and Point Conception, California) revealed particles with abundances on the order of 10 and 10(5) 1(-1) and ranging in size from 10 to 10(5) mu m(2). The particles varied in the types of organisms attached, the internal structure and probable biological sources. Field observations and laboratory experimental manipulations suggest varied sources and mechanisms of formation. These particles are potential hot spots of organic matter, microbial diversify and interactions, and, depending on their size and sinking rates, serve as conduits for carbon export to the ocean's interior
J.-P. Azam, C. Morrisson, J. Klugman, B. Neyapti, F. Stewart et A. Goudie, Conflits et croissance en Afrique
No full textGrellet Gérard. J.-P. Azam, C. Morrisson, J. Klugman, B. Neyapti, F. Stewart et A. Goudie, Conflits et croissance en Afrique. In: Tiers-Monde, tome 40, n°160, 1999. Études sur la pauvreté, prix agricoles et filières intégrées, nationalistes hindous et développement... pp. 951-952
Health impact of dietary selenium nanoparticles on mahseer fish
No full textQuaid I Azam Univ, Fisheries & Aquaculture Lab, Dept Anim Sci, Fac Biol Sci, Islamabad, PakistanUNESP, Ctr Aquicultura, Jaboticabal, SP, BrazilQuaid I Azam Univ, Natl Ctr Phys, Islamabad 45320, PakistanUNESP, Ctr Aquicultura, Jaboticabal, SP, Brazi
High-resolution imaging of pelagic bacteria by Atomic Force Microscopy and implications for carbon cycling
No full textIn microbial oceanography, cell size, volume and carbon (C) content of pelagic bacteria and archaea ('bacteria') are critical parameters in addressing the in situ physiology and functions of bacteria, and their role in the food web and C cycle. However, because of the diminutive size of most pelagic bacteria and errors caused by sample fixation and processing, an accurate measurement of the size and volume has been challenging. We used atomic force microscopy (AFM) to obtain high-resolution images of pelagic bacteria and Synechococcus. We measured the length, width and height of live and formalin-fixed pelagic bacteria, and computed individual cell volumes. AFM-based measurements were compared with those by epifluorescence microscopy (EFM) using 4',6-diamidino-2-phenylindole (DAPI). The ability to measure cell height by AFM provides methodological advantage and ecophysiological insight. For the samples examined, EFM (DAPI)-based average cell volume was in good agreement (1.1-fold) with live sample AFM. However, the agreement may be a fortuitous balance between cell shrinkage due to fixation/drying (threefold) and Z-overestimation (as EFM does not account for cell flattening caused by sample processing and assumes that height width). The two methods showed major differences in cell volume and cell C frequency distributions. This study refines the methodology for quantifying bacteria-mediated C fluxes and the role of bacteria in marine ecosystems, and suggests the potential of AFM for individual cell physiological interrogations in natural marine assemblages. The ISME Journal (2010) 4, 427-439; doi:10.1038/ismej.2009.116; published online 26 November 200
Buckypaper of polyvinyl chloride/<i>p</i> -phenylenediamine modified graphite and PVC/graphite <i>via</i> resin infiltration technique
No full textResin-infiltration technique has been employed as a versatile method to improve nanofiller dispersion in matrix. In this article, fabrication of polyvinyl chloride (PVC)/p-phenylenediamine (PPD)/functional graphite (F-G) and PVC/F-G composite paper have been reported through resin-infiltration techniques. Synthesis and characterization of PVC/PPD/F-G and PVC/F-G composite papers for enhanced structural, morphological, thermal, hardness, wettability, and conductivity properties have been studied. Moreover, the effect of increasing amount of F-G and PPD/F-G nanofiller on composite paper properties was scrutinized and compared. Transmission electron microscopy and scanning electron microscopy depicted better graphite nanofiller dispersion in PVC matrix and network formation in PVC/PPD/F-G composite paper. Maximum degradation temperature (T-max) of PVC/PPD/F-G 0.08 composite paper (517 degrees C) was found higher than PVC/F-G 0.08 composite paper (484 degrees C). Dynamic contact angle analysis shows that the PVC/PPD/F-G and PVC/F-G composite papers have better surface wettability than neat PVC. PVC/PDD/F-G 0.1 and PVC/F-G 0.1 composite papers possess high microhardness values up to 39.67 and 32.76Hv, respectively. Electrical conductivity of 8.97 x 10(-3) and 5.89 x 10(-3) Sm-1 was observed for 0.08 wt% PPD/F-G and F-G loaded samples. POLYM. COMPOS., 39:4176-4187, 2018. (c) 2017 Society of Plastics EngineersShanghai Univ, Res Ctr Nano Sci & Technol, Shanghai 200444, Peoples R ChinaQuaid I Azam Univ Campus, Natl Ctr Phys, Nanosci & Technol Dept, Islamabad, PakistanQuaid I Azam Univ, Dept Chem, Islamabad, PakistanGomal Univ, Inst Chem Sci, Dera Ismail Khan, PakistanUNSEP Univ Estadual Paulista, Inst Chem, Dept Analyt Chem, BR-14801970 Araraquara, SP, BrazilUNSEP Univ Estadual Paulista, Inst Chem, Dept Analyt Chem, BR-14801970 Araraquara, SP, Brazi
Individual cell DNA synthesis within natural marine bacterial assemblages as detected by 'click' chemistry
No full textIndividual cell growth rates enhance our understanding of microbial roles in regulating organic matter flux in marine and other aquatic systems. We devised a protocol to microscopically detect and quantify bacteria undergoing replication in seawater using the thymidine analog 5-ethynyl-2'-deoxyuridine (EdU), which becomes incorporated into bacterial DNA and is detected with a 'click' chemistry reaction in 3 orders of magnitude, wherein the most intensely labeled cells comprised most of a sample's sum community EdU signal, e.g. 26% of cells comprised 80% of the sum signal. This ability to rapidly detect and quantify signals in labeled DNA is an important step toward a robust approach for the determination of single-cell growth rates in natural assemblages and for linking growth rates with microscale biogeochemical dynamics
Quantitative role of shrimp fecal bacteria in organic matter fluxes in a recirculating shrimp aquaculture system
No full textMicroorganisms play integral roles in the cycling of carbon (C) and nitrogen (N) in recirculating aquaculture systems (RAS) for fish and shellfish production. We quantified the pathways of shrimp fecal bacterial activities and their role in C- and N-flux partitioning relevant to culturing Pacific white shrimp, Penaeus (Litopenaeus) vannamei, in RAS. Freshly produced feces from P. vannamei contained 0.6-7 x 1010 bacteria g-1 dry wt belonging to Bacteroidetes (7%), Alphaproteobacteria (4%), and, within the Gammaproteobacteria, almost exclusively to the genus Vibrio (61%). Because of partial disintegration of the feces (up to 27% within 12 h), the experimental seawater became inoculated with fecal bacteria. Bacteria grew rapidly in the feces and in the seawater, and exhibited high levels of aminopeptidase, chitinase, chitobiase, alkaline phosphatase, alpha- and beta-glucosidase, and lipase activities. Moreover, fecal bacteria enriched the protein content of the feces within 12 h, potentially enriching the feces for the coprophagous shrimp. The bacterial turnover time was much faster in feces (1-10 h) than in mature RAS water (350 h). Thus, shrimp fecal bacteria not only inoculate RAS water but also contribute to bacterial abundance and productivity, and regulate system processes important for shrimp health
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