Abundance Of Aggregates Research Articles

Ecology of Young Stream Resident Warner Sucker (Catostomus warnerensis) in Warner Basin, Oregon

We visually censused Warner sucker cohorts in a low gradient stream reach and determined microhabitat use from random availability data. For above-water visual censuses (AVC), we counted aggregations while slowly wading through Honey Creek three times both years. Underwater visual censuses (UVC) were done in 1993 by snorkeling. Mean focal point velocity (FPV) during AVC significantly differed by year but not by census date, and mean depth did not differ for either. In 1993 we found suckers used microhabitats with FPV between >3 to 6 cm/s (χ12 = 3.93, P < 0.05) and depth between >20 to 40 cm (χ12 = 4.5, P < 0.05). Suckers avoided areas where FPV exceeded 15 cm/s (χ12 = 18.7, P < 0.001) and depth between >60 to 80 cm (χ12 = 8.1, P < 0.005). Aggregate abundance was significantly related to both distance to (r64 = −0.45, P = 0.0002) and percentage (r64 = 0.44, P = 0.0003) submerged vegetation. We found 97% of suckers (N/m3) in riffle/run habitat during UVC. When mean flow was used as a continuous variable, we found suckers occupied habitats >3 cm3/s and avoided habitats <2 cm3/s in a disproportionate manner relative to availability. These results suggest young suckers select vegetated areas with moderate flow and relatively shallow depths during first few months of life. This information improves our understanding of ecological habits of early life stages of a rare western catostomid during stream residence, which could be useful for conservation management in low gradient stream reaches of Warner Basin.

The Alexander Disease–Causing Glial Fibrillary Acidic Protein Mutant, R416W, Accumulates into Rosenthal Fibers by a Pathway That Involves Filament Aggregation and the Association of αB-Crystallin and HSP27

Here, we describe the early events in the disease pathogenesis of Alexander disease. This is a rare and usually fatal neurodegenerative disorder whose pathological hallmark is the abundance of protein aggregates in astrocytes. These aggregates, termed "Rosenthal fibers," contain the protein chaperones alpha B-crystallin and HSP27 as well as glial fibrillary acidic protein (GFAP), an intermediate filament (IF) protein found almost exclusively in astrocytes. Heterozygous, missense GFAP mutations that usually arise spontaneously during spermatogenesis have recently been found in the majority of patients with Alexander disease. In this study, we show that one of the more frequently observed mutations, R416W, significantly perturbs in vitro filament assembly. The filamentous structures formed resemble assembly intermediates but aggregate more strongly. Consistent with the heterozygosity of the mutation, this effect is dominant over wild-type GFAP in coassembly experiments. Transient transfection studies demonstrate that R416W GFAP induces the formation of GFAP-containing cytoplasmic aggregates in a wide range of different cell types, including astrocytes. The aggregates have several important features in common with Rosenthal fibers, including the association of alpha B-crystallin and HSP27. This association occurs simultaneously with the formation of protein aggregates containing R416W GFAP and is also specific, since HSP70 does not partition with them. Monoclonal antibodies specific for R416W GFAP reveal, for the first time for any IF-based disease, the presence of the mutant protein in the characteristic histopathological feature of the disease, namely Rosenthal fibers. Collectively, these data confirm that the effects of the R416W GFAP are dominant, changing the assembly process in a way that encourages aberrant filament-filament interactions that then lead to protein aggregation and chaperone sequestration as early events in Alexander disease.

Physical and biogeochemical controls of microaggregate dynamics in a tidally affected coastal ecosystem

Tidal flat ecosystems exhibit pronounced tidal currents that cause high loads of suspended matter (SPM) and intense sedimentation. To identify systematic patterns of tidal SPM dynamics and the significance of physical forcing versus microbial processes in aggregation processes, we conducted a comprehensive study from January 2002 to October 2004 in a backbarrier tidal flat area of the German Wadden Sea. Further, various aggregate fractions were separated by their settling properties in June and October 2004, applying a new sampling device. Tidal dynamics of SPM, particulate organic carbon (POC), aggregate abundance and size, chlorophyll a (Chl a), the carbon to nitrogen ratio (C : N), numbers of bacteria, and DOC often exceeded seasonal dynamics of the tidal means of these properties. SPM, POC, Chl a, and aggregate abundance were positively correlated and aggregate size negatively correlated to the current. DOC concentrations and total bacterial numbers exhibited minima at high tide and maxima at low tide. Aggregate quality—i.e., POC : SPM, Chl a, size, amino acid content, and bacterial colonization—varied tidally among the fractions, relative to bulk SPM and was different in June and October. In June, tidal dynamics of these properties and bacterial biomass production were higher than in October. Aggregate abundance was substantially lower during the growing season and aggregate size larger than in fall and winter. Microbial processes were important during the growing season in affecting tidal dynamics of aggregation and sedimentation, whereas in fall and winter, physical forcing was the main factor controlling aggregate dynamics.

Immunohistochemistry of thrombi following iliac venous stenting: A novel model of venous thrombosis

Stenting has become a common intervention for venous occlusive disease. Little is known regarding the composition of venous thrombi complicating stent placement. The optimal design of antithrombotic agents in this setting requires this knowledge. Quantitative immunohistochemistry was undertaken to define the platelet, fibrin(ogen) and leukocyte composition and spatial orientation of venous thrombi following percutaneous iliac stent placement in pigs. Venous stent thrombus size was measured by weight and scintillation detection of autologous (111) In-platelets. Thrombi were divided in segments (cephalad to caudad), sectioned and stained with monoclonal anti-platelet glycoprotein Ib or polyclonal anti-fibrin(ogen) fluorescent antibodies. Thrombus platelet content was 100-fold greater than paired whole blood samples. The caudal-most segments contained platelet-rich aggregates (p < 0.05) with abundant leukocytes (p < 0.0001) relative to more cephalad segments. Platelet and fibrin(ogen) content varied over an eight-fold range between segments but were directly correlated with each other (r = 0.77; p < 0.0001). The platelet co-localization with fibrin(ogen) is consistent with the phospholipid dependence of prothrombin activation. The abundance and caudal distribution of platelet-leukocyte aggregates indicate their preferential accretion from flowing blood early in the genesis of venous stent thrombi. These may represent novel cellular targets for the prevention and treatment of venous thrombosis.

Conversion of a CHO cell culture process from perfusion to fed-batch technology without altering product quality

During the development of a new drug product, it is a common strategy to develop a first-generation process with the aim to rapidly produce material for pre-clinical and early stage clinical trials. At a later stage of the development, a second-generation process is then introduced with the aim to supply late-stage clinical trials as well as market needs. This work was aimed at comparing the performance of two different CHO cell culture processes (perfusion and fed-batch) used for the production of a therapeutically active recombinant glycoprotein at industrial pilot-scale. The first-generation process was based on the Fibra-Cel packed-bed perfusion technology. It appeared during the development of the candidate drug that high therapeutic doses were required (>100mg per dose), and that future market demand would exceed 100 kg per year. This exceeded by far the production capacity of the first-generation process, and triggered a change of technology from a packed-bed perfusion process with limited scale-up capabilities to a fed-batch process with scale-up potential to typical bioreactor sizes of 15m(3) or more. The productivity per bioreactor unit volume (in product m(-3)year(-1)) of the fed-batch process was about 70% of the level reached with the first-generation perfusion process. However, since the packed-bed perfusion system was limited in scale (0.6m(3) maximum) compared to the volumes reached in suspension cultures (15m(3)), the fed-batch was selected as second-generation process. In fact, the overall process performance (in product year(-1)) was about 18-fold higher for the fed-batch compared to the perfusion mode. Data from perfusion and fed-batch harvests samples indicated that comparable product quality (relative abundance of monomers dimers and aggregates; N-glycan sialylation level; isoforms distribution) was obtained in both processes. To further confirm this observation, purification to homogeneity of the harvest material from both processes, followed by a complementary set of studies (e.g. full physico-chemical characterization, assessment of in vitro and in vivo bioactivity, comparative pharmacokinetics and pharmacodynamics studies in relevant species, etc.) would be required. Finally, this illustrates the need to fix the production process early during the development of a new drug product in order to minimize process conversion efforts and to shorten product development time lines.

Mechanism of a rainfall-induced slide-debris flow: constraints from microstructure of its slip zone

The microstructure of the slip zone of a rainfall-induced slide-debris flow landslide, developed within a volcanic saprolitic soil, was comprehensively investigated using optical and backscattered electron microscopy (BEM) techniques, and a digital image analysis system. The slip zone had generally looser structure with higher relative porosities and greater abundance of discrete kaolinite aggregates than its confining materials. Particles are generally random or weakly arranged. Distinct microstructural characteristics suggest that the slip zone has undergone dilation and microstructural destruction. The dilative deformation should have began at the tip of tensions crack(s), where high pore water pressure was generated during heavy rainfall, and gradually propagated down the slope under sustained water level in these crack(s). The soil in the dilated zone should have facilitated shear deformation during which it experienced contraction under undrained conditions. Rapid and significant increase of pore water pressure within the toe section of the slip zone and sudden release of strain inhibited by the shotcrete cover should have been responsible for the transformation of the fore mass of the slide into a debris flow. During sliding, particle movement within the slip zone should have taken place as a fluid-like particulate flow, resulting in a random or weak particle alignment in general.

A new sampling device for microaggregates in turbid aquatic systems

Microaggregates (5 to 500 µm) are the main component of suspended particulate matter in shallow and turbid aquatic environments. Whereas their abundance and size structure have been studied by various optical systems, their composition, aggregation and disaggregation processes, and microbial colonization have been studied only little. This is largely due to inadequate sampling devices for microaggregates. Therefore, we established a new device, allowing the careful collection and documentation of aggregate size and abundance by laser illumination and a regular digital camera. The instrument simultaneously serves as a settling chamber to separate and subsample microaggregate fractions, differing in their settling velocities. Thus, it provides material for studying the biological and chemical composition and microbial colonization of microaggregates with a minimum of manipulation. First results from its application during a semitidal cycle in the German Wadden Sea demonstrate that it yields reliable results of the abundance and size structure of aggregates, reflecting the tidal changes in the hydrodynamic conditions. Total aggregate abundance covaried with dry weight of suspended particulate matter and turbidity. The biological and chemical analysis of aggregate fractions separated during 45 min of settling, showed that the various fractions exhibited distinct differences with respect to aggregate size, dry weight, particulate organic carbon, the carbon per nitrogen ratio (by weight), number of bacteria and bacterial production rates per aggregate. Hence, the application of this sampling device will lead to better insight into the dynamics and qualitative changes of microaggregates in turbid aquatic systems and deepen our understanding of their overall significance in these ecosystems.

Treatment with calcitonin prevents the net loss of collagen, hyaluronan and proteoglycan aggregates from cartilage in the early stages of canine experimental osteoarthritis

To evaluate the effect of calcitonin (CT) on the histology and biochemistry of articular cartilage from unstable operated and nonoperated knee in a canine model of experimental osteoarthritis (OA). Eighteen dogs underwent anterior cruciate ligament transection (ACLT) of the right knee and were randomly distributed into three groups of six dogs each. From day-1 after surgery until sacrifice 84 days post-ACLT, each dog received a daily nasal spray that delivered the placebo, 100 units of CT or 400 units of CT. Histologic lesions were scored. Hyaluronan (HA) and antigenic keratan sulfate (AgKS) were quantified by enzyme-linked immunosorbent assays (ELISAs), whereas aggrecan molecules extracted under nondissociative conditions were characterized by velocity gradient centrifugation. All canine cruciate-deficient knees developed OA. At a daily dose of 400 units, CT had no effect on the size of osteophytes but significantly reduced the severity of cartilage histologic lesions in unstable knees. CT also enhanced the HA content as well as the size distribution and relative abundance of fast-sedimenting aggrecan aggregates in cartilage from both operated and nonoperated knees. On the other hand, in the CT-treated group, the cartilage content of AgKS increased in operated joints, but not in nonoperated joints. Because CT delivered as a nasal spray markedly reduced the severity of most OA changes, both at the histological and biochemical level, this form of therapy may have benefits for humans who have recently experienced a traumatic knee injury, and as well as for dogs who spontaneously rupture their ACL.

Optimization of the medium perfusion rate in a packed-bed bioreactor charged with CHO cells

In the present study, the optimal medium perfusion rate to be used for the continuous culture of a recombinant CHO cell line in a packed-bed bioreactor made of Fibra-Cel((R)) disk carriers was determined. A first-generation process had originally been designed with a high perfusion rate, in order to rapidly produce material for pre-clinical and early clinical trials. It was originally operated with a perfusion of 2.6 vvd during production phase in order to supply the high cell density (2.5x10(7) cell ml(-1) of packed-bed) with sufficient fresh medium. In order to improve the economics of this process, a reduction of the medium perfusion rate by -25% and -50% was investigated at small-scale. The best option was then implemented at pilot scale in order to further produce material for clinical trials with an improved second-generation process. With a -25% reduction of the perfusion rate, the volumetric productivity was maintained compared to the first-generation process, but a -30% loss of productivity was obtained when the medium perfusion rate was further reduced to -50% of its original level. The protein quality under reduced perfusion rate conditions was analyzed for purity, N-glycan sialylation level, abundance of dimers or aggregates, and showed that the quality of the final drug substance was comparable to that obtained in reference conditions. Finally, a reduction of -25% medium perfusion was implemented at pilot scale in the second-generation process, which enabled to maintain the same productivity and the same quality of the molecule, while reducing costs of media, material and manpower of the production process. For industrial applications, it is recommended to test whether and how far the perfusion rate can be decreased during the production phase - provided that the product is not sensitive to residence time - with the benefits of reduced cost of goods and to simplify manufacturing operations.

현장입도분석기를 이용한 섬진강하구 부유퇴적물의 특성 연구

In situ particle size and volume concentration of suspended sediment was measured at the mouth of Seomjin River Estuary In February 2001, using an optical instrument, 'LISST-100'. Time variation of in situ particle size and concentration shows: (1) during ebb tide, Seomjin River supplies relatively fine-grained particles with less-fluctuated, compared to during flood tide, and well-behaved concentrations following the tidal cycle; and (2) during flood tide, relatively coarse-grained particles with highly variable in size distribution and concentration flow upstream from Kwangyang Bay. This explains a poor correlation <TEX>$(r^{2}=0.10)$</TEX> between sediment concentration and beam attenuation coefficient during flood and a high degree of correlation <TEX>$(r^{2}=0.80)$</TEX> during ebb tide. Relatively fine grained and well defined, monotonous size distribution may promote the correlation between concentration and beam attenuation coefficient due to optical homogeneity of particles during ebb tide. Abundance of large aggregates with time-varying size and shape distributions may be mainly responsible for variations in optical properties of the sediment during flood tide, and thus may confound the relationship between the two variables. The difference in particle sizes and shapes between flood and ebb tides can also be observed on SEM images.

Deformation History of a Landslide Slip Zone in Light of Soil Microstructure

Research Article| February 01, 2004 Deformation History of a Landslide Slip Zone in Light of Soil Microstructure BAO-PING WEN; BAO-PING WEN 12Department of Hydraulic and Hydropower Engineering, Tsinghua University, Beijing 100084, China Search for other works by this author on: GSW Google Scholar ADNAN AYDIN ADNAN AYDIN 3Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China Search for other works by this author on: GSW Google Scholar Author and Article Information BAO-PING WEN 12Department of Hydraulic and Hydropower Engineering, Tsinghua University, Beijing 100084, China ADNAN AYDIN 3Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China Publisher: Association of Environmental & Engineering Geologists First Online: 02 Mar 2017 Online ISSN: 1558-9161 Print ISSN: 1078-7275 © 2004 Association of Engineering Geologists Environmental & Engineering Geoscience (2004) 10 (2): 123–149. https://doi.org/10.2113/10.2.123 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation BAO-PING WEN, ADNAN AYDIN; Deformation History of a Landslide Slip Zone in Light of Soil Microstructure. Environmental & Engineering Geoscience 2004;; 10 (2): 123–149. doi: https://doi.org/10.2113/10.2.123 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract The microstructure of a slip zone from a recent landslide was investigated by combined optical microscopy (OPM) and backscattered electron microscopy (BEM) techniques. Along the toe of the slope, the slip zone consisted of two distinct segments, formed a) along a pre-existing slip zone and b) through completely decomposed granite (CDG), both of which comprise composite soils. The microstructural features were systematically captured, quantified, and analyzed using an advanced image-analysis system. It is shown that variations in density, porosity, presence of matching fragments of coarse particles, abundance of tabular aggregates and plates of kaolinite and particle alignment are significant indicators of the deformation history of the slip zone. The results indicate that multiple processes concurred in the course of deformation: compaction and dilation, cataclasis and comminution, and particle rearrangement. Such deformation features of the natural composite soils are fundamentally different from the relatively simple soils commonly used in laboratory studies. The extent of each process depends on the particle-size distribution and stress level that prevailed at time of failure. The particle movement and microstructural evolution of the slip zone could be described as particulate flow through simultaneous bulk simple shear and pure shear. Depending on their relative abundance, fine particles play an important but variable role in the development of the slip zone and the mobilization of its shear resistance to deformation. Reactivation and/or prolonged deformation evidently change the deformation behavior of the pre-existing slip zone. In general, shape-preferred orientation of particles occurs where they are obviously aligned. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The relationship between floc area and backscatter during a spring phytoplankton bloom

A 10-week study during the spring phytoplankton bloom in Bedford Basin, Nova Scotia showed two different linear functional relationships between estimates of the in situ particulate backscatter coefficient ( b bp) and the projected area concentration of particles larger than 100 μm . In the first part of the study (26 February–19 March, 1998), b bp increased more rapidly with floc projected area concentration than it did during the second part of the study (26 March–30 April, 1998). The observed change in relationship was accompanied by an increase in both size and abundance of large particle aggregates in the second part of the study and an inferred shift to more organic bulk particle composition during and after the bloom, also the second part of the study. A simple conceptual model explains these observations. Before the bloom, suspended particles in Bedford Basin were primarily inorganic. As the bloom began and progressed, organic particles became dominant and detrital particles began to aggregate to form flocs.

Free and Particle‐associated Extracellular Enzyme Activity and Bacterial Production in the Lower Elbe Estuary, Germany

AbstractA high abundance of particles and aggregates is a characteristic of estuaries and may represent important loci of increased bioproductivity and microbial activity. From a survey performed in the Elbe estuary, particle concentration (using a particle counter), bacterial biomass and abundance (AODC method), bacterial production rates ([3H] thymidine method) and the microbial extracellular enzyme activity of 11 enzymes (MUF and MCA method) were determined with particular respect to their relationship to particles and aggregates (sizefractionated). Although higher particle abundance was found compared to other sections of the river Elbe, neither relative nor absolute bacterial activity associated with particles and aggregates was enhanced. The activity of free dissolved microbial enzymes was found to dominate the breakdown of organic material. The productivity of free dispersed bacteria ≥0.2…&lt;2 μm (2…69%) and bacteria attached to small particles ≥2…&lt;10 μm (27…93%) considerably surpassed that of bacteria associated with particles &gt;10 μm (0…40%). This indicates that the larger particles and aggregates do not always contribute substantially to the overall microbial activity in rivers and estuaries.

Distribution Patterns and Size–Age Composition in Aggregations of the Gastropod Mollusk Nucella heyseana in Peter the Great Bay, Sea of Japan

Gastropods Nucella heyseana were collected from 1999 to 2001 from different habitats in Vostok Bay (Sea of Japan). The spatial distribution, the seasonal and interannual dynamics, and the composition of aggregations of this mollusk were analyzed. In Vostok Bay, N. heyseana inhabits biotopes that are typical of this species and other members of the genus and sometimes forms aggregations with an unusually high density and biomass (up to 1690 spec/m2 and 3680 g/m2), thus exceeding 10–40 times the greatest values reported elsewhere for populations of the southern Kuril Islands and Pos'eta Bay (Sea of Japan). N. heyseana is a typical polyphagous predator, and its diet includes numerous species of the associated fauna of bivalve and gastropod mollusks (more than 30 species). The abundance, composition, and stability of local aggregations of N. heyseana are largely dependent on the abundance dynamics of its prey (primarily the most common species, such as Mytilus trossulus, Ruditapes philippinarum, Protothaca euglypta, and Littorina spp.). The opinion on the low density of N. heyseana in southern Primorye (Golikov, Kussakin, 1978) is probably based on a lack of information about the intertidal fauna of this region compared to the South Kuril Islands.

Abundance, distribution and sinking rates of aggregates in the Ross Sea, Antarctica

The vertical distribution and temporal changes in aggregate abundance and sizes were measured in the Ross Sea, Antarctica, during two field seasons, one in austral spring 1994 and one in early summer, 1995/96. Aggregate abundance, size and potential sinking rates were determined by photographic techniques. Measurements of water column parameters, including particulate organic carbon concentrations, were assessed simultaneously, as was the flux of organic matter with floating sediment traps. The numbers of aggregates (and to a lesser extent their size) increased with time, although there was substantial spatial variability in these variables at any point in time. Some aggregates appeared to sink extremely rapidly, and for these, our photographic measurements were able to estimate only a minimum sinking rate, which equaled 288 m d −1. Estimates of aggregate organic carbon flux were compared to those determined by floating sediment traps. From these results, aggregate fluxes appear to have dominated the vertical export of organic matter from the euphotic zone. The genesis and flux of aggregates in the Ross Sea are the critical processes controlling the export of biogenic material from the surface layer.

Characteristics, Dynamics and Importance of Aggregates in Rivers - An Invited Review

The current knowledge of micro- and macroaggregates in running waters as well as an assessment of their importance will be given in this overview. Micro- and macroscopic aggregates are an abundant component of running waters, considering both rivers and estuaries. They are composed of different kinds of organic and inorganic matter and elements, mainly from the aquatic but also from the terrestrial environment. Their production is determined by natural and anthropogenically influenced abiotic and biotic factors. Aggregate abundance, size and composition vary greatly along the longitudinal profile of running waters. Aggregates are actively or passively colonized by bacteria, protozoa (amoebae, ciliates and flagellates) and metazoa (copepods, nematodes, rotifers, veliger larvae) and they show higher loads of nutrients and organisms compared to the surrounding water. Detritus in running waters has been examined over a period of 100 years but investigations of single aggregates began only in 1996, after pioneering works in the marine field and in lakes. Since then studies have been focused on several aspects of aggregate formation, colonization, nutrient recycling and decomposition. Aggregates have been identified as foci of microbial activity. It has been shown that the significance of aggregate – associated organisms and processes varies both temporally and spatially and is also affected by the nutrient status of surrounding water. An important conclusion from recent studies is that the resuspension and sedimentation of aggregates connects pelagic and benthic food webs to an aquatic food web. It also underlines the importance of the microbial food web, with its fluxes among aggregate-associated pico- and nano-organisms, to organisms of higher trophic levels. Predators of higher trophic levels are only able to eat small-sized organisms if they are associated to aggregates.

Microbial ecology of organic aggregates in aquatic ecosystems

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 28:175-211 (2002) - doi:10.3354/ame028175 Microbial ecology of organic aggregates in aquatic ecosystems Meinhard Simon1,*, Hans-Peter Grossart1, Bernd Schweitzer1, Helle Ploug2,** 1Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, 26111 Oldenburg, Germany 2Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark *E-mail: m.simon@icbm.de **Present address: Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany ABSTRACT: Macroscopic organic aggregates, which are >500 μm and known as marine and lake snow, are important components in the turnover, decomposition and sinking flux of both organic and inorganic matter and elements in aquatic ecosystems. They are composed of various organic and inorganic materials depending largely on the given system and environmental conditions. The systems include the pelagic limnetic, the neritic and oceanic marine region, as well as shallow turbid environments, e.g. rivers, the littoral zone of lakes, estuaries and tidally affected coastal areas with intense turbulence and a high load of suspended matter. Aggregate abundance and size vary greatly among these systems. Macroaggregates are heavily colonized by bacteria and other heterotrophic microbes and greatly enriched in organic and inorganic nutrients as compared to the surrounding water. During the last 15 yr, many studies have been carried out to examine various aspects of the formation of aggregates, their microbial colonization and decomposition, nutrient recycling and their significance for the sinking flux. They have been identified as hot-spots of the microbial decomposition of organic matter. Further, microaggregates, which are <5 to 500 μm in size and stained by different dyes, such as transparent exopolymer particles (TEP) and Coomassie blue-stained particles, have been discovered and shown also to be important in the formation and decomposition of macroaggregates. In this review we give an overview of the present state of the microbial ecology of macro- and microaggregates, including the mentioned points but highlighting in particular the recent findings on the bacterial colonization of aggregates using molecular tools, their microbial decomposition and mineralization, and the significance of protozoans and metazoans for the colonization and decomposition of macroaggregates. Today it is evident that not only the aggregates but also their surroundings are sites and hot-spots of microbial processes, with the plume of solutes leaking out of the aggregates and greatly extending the volume of the intense decomposition processes. This microheterogeneity has important implications for the spatial and temporal dynamics of the organic-matter field in aquatic ecosystems and for our understanding of how heterotrophic organisms are involved in the decomposition of organic matter. The significance of aggregate-associated microbial processes as key processes and also for the overall decomposition and flux of organic mattervaries greatly among the various systems, and is greatly affected by the total amount of suspended particulate matter. A conclusion from the presented studies and results is that the significance of bacteria for the formation and decomposition of aggregates appears to be much greater than previously estimated. For a better understanding of the functioning of aquatic ecosystems it is of great importance to include aggregate-associated processes in ecosystem modeling approaches. KEY WORDS: Aggregates · Transparent exopolymer particles · Particulate organic matter · Algae · Bacteria · Zooplankton · Sinking flux · Dissolved organic matter Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 28, No. 2. Online publication date: June 26, 2002 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2002 Inter-Research.

Microbial communities and respiration on aggregates in the Elbe Estuary, Germany

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 27:241-248 (2002) - doi:10.3354/ame027241 Microbial communities and respiration on aggregates in the Elbe Estuary, Germany Helle Ploug1,*, Heike Zimmermann-Timm2,**, Bernd Schweitzer3 1Max Planck Institute for Marine Microbiology, Celsiusstraße 1, 28359 Bremen, Germany 2Institute for Hydrobiology and Fisheries, University of Hamburg, Zeiseweg 9, 22765 Hamburg, Germany 3Institute for Limnology, University of Konstanz, Postbox 5560, 78434 Konstanz, Germany *E-mail: hploug@mpi-bremen.de **Present address: Institute for Ecology, Department for Limnology, Friedrich-Schiller-University of Jena, Winzerlaerstraße 10, 07743 Jena, Germany ABSTRACT: Estuaries are characterized by a very high abundance of small aggregates enriched with bacteria, protozoa and sometimes metazoa compared to their abundance in the surrounding water. In this study, the microbial community and respiration rates on estuarine aggregates were analyzed by the combination of microscopy (bacteria, protozoa and metazoa enumeration), in situ hybridization and microsensor techniques. Aggregates were isolated and kept in darkness to prevent scavenging or production of new organic carbon. Bacterial abundance and respiration rates were stable during the first 2 d after collection. Bacterial numbers ranged from 0.84 x 106 to 23.7 x 106 cells aggregate (agg)-1. Protozoa were dominated by nanoflagellates, which varied between 24 and 1497 cells agg-1. Total protozoan biovolume accounted on average for 4 to 13% of the total estimated microbial biomass on aggregates, and the total grazing rate on attached bacteria was apparently low. Size-specific respiration rates were described by R = 5.86 x d1.82, where R is measured in ngC agg-1 h-1 and the diameter (d) is measured in mm. The average respiration rate was 0.150 μgC agg-1 d-1, and the estimated average bacterial respiration rate was 22 fgC cell-1 d-1. Total respiration and cell-specific respiration decreased to 0.039 μgC agg-1 d-1 and 2.6 fgC cell-1 d-1, respectively, after 6 d. The bacterial community was dominated by members of b-proteobacteria and the Cytophaga-Flavobacterium cluster, which together accounted for 54% of all 4',6-diamidino-2-phenylindole (DAPI) stained bacteria at the end of the study. The respiration rate on aggregates larger than 400 μm in the water column of the Elbe Estuary was 11.8 μgC l-1 h-1 as determined from the size-specific respiration rates, the aggregate abundance and size distribution. It accounted for 84 to 94% of the estimated total respiration in the upper water column. The critical ambient O2 concentration, at which the center of the aggregate interior turns anoxic, was found at ~16 μM. KEY WORDS: Estuarine aggregates · Oxygen microelectrodes · Respiration · Protozoa · Bacteria · In situ hybridization Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 27, No. 3. Online publication date: April 16, 2002 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2002 Inter-Research.

Vertical Distribution of the Far East Trepang Apostichopus japonicusin Vostok Bay, Sea of Japan

The abundance, weight, and age structure of aggregations of the Far East trepang Apostichopus japonicuswere studied in Vostok Bay, Sea of Japan, during the first part of September 2000. The highest density of aggregations (8.3 ± 0.5 ind/m2) and biomass (131.88 ± 10.50 g/m2) of animals was characteristic for coastal sites at the depth 0.5–1.5 m. With anincrease in depth the biomass and density of A. japonicusreduced 1.5 and 3 (depth 5–6 m), 220 and 830 times (depth 8–15 m) respectively. The ratio of large animals concurrently increased in the aggregation structure. The specifics of the distribution and spatial variability of the aggregation structure are discussed in relation to uncontrolled fishing of holothurians of large sizes.

Fragmentation of marine snow by swimming macrozooplankton: A new process impacting carbon cycling in the sea

Comparisons of the abundances and size distributions of marine snow (aggregated particles >0.5 mm in diameter) in the upper 100 m of the water column at ten stations off Southern California in the late afternoon with those in the same parcel of water the following morning, after nocturnal vertical migration by zooplankton had occurred, revealed the existence of a previously undescribed process affecting marine particle dynamics. Aggregate abundances increased overnight and changes were positively and significantly correlated only with the abundance of the common euphausiid, Euphausia pacifica, and with no other biological or physical factor. Moreover, mean aggregate size decreased and aggregate size distributions shifted toward smaller size classes when euphausiids were abundant. The only conclusion consistent with these findings was that euphausiids were physically disaggregating marine snow into smaller, more numerous aggregates through shear stresses generated while swimming. Video-recording of both tethered and free-swimming E. pacifica in the laboratory dramatically confirmed that aggregates passing within 8–10 mm of the animal's abdomen were fragmented either by entrainment and direct impact with the beating pleopods or by eddies generated during swimming. At the abundances observed in this study, swimming E. pacifica would have sufficiently disturbed 3–33% of the water column each night to disrupt the aggregates contained therein. This is the first evidence for the fragmentation of large particles by the swimming activities of zooplankton and suggests that macrozooplankton and micronekton play a significant role in the particle dynamics of the water column regardless of whether they consume particles or not. Disaggregation of marine snow by swimming and migrating animals may alter the sizes of particles available to grazers and microbial colonizers and reduce the flux of particulate carbon by generating smaller particles, which potentially sink more slowly and reside longer in the water column. This newly discovered process reduces carbon flux while simultaneously conserving carbon and provides a previously unconsidered link between animal behavior and the biogeochemistry of the sea. It may help explain the exponential reduction in particle flux with depth observed in parts of the ocean and help balance oceanic carbon models.