Heterotrophic Production Research Articles

The influence of autotrophy, heterotrophy and temperature on pelagic food web efficiency in a brackish water system

Climate change has been suggested to lead to higher temperature and increased heterotrophy in aquatic systems. The aim of this study was to test how these two factors affect metazooplankton and food web efficiency (FWE was defined as metazooplankton production divided by basal production). We tested the following hypotheses: (1) that lower metazooplankton production and lower FWE would be found in a food web based on heterotrophic production (bacteria) relative to one based on autotrophic production (phytoplankton), since the former induces a larger number of trophic levels; (2) the metazooplankton in the heterotrophic food web would contain less essential fatty acids than those from the autotrophic food web; and (3) that higher temperature would lead to increased FWE. To test these hypotheses, a mesocosm experiment was established at two different temperatures (5 and 10°C) with a dominance of either autotrophic (NP) or heterotrophic basal production (CNP). Metazooplankton production increased with temperature, but was not significantly affected by differences in basal production. However, increased heterotrophy did lead to decreased fatty acid content and lower individual weight in the zooplankton. FWE increased with autotrophy and temperature in the following order: 5CNP < 10CNP < 5NP < 10NP. Our results indicate that in the climate change scenario we considered, the temperature will have a positive effect on FWE, whereas the increase in heterotrophy will have a negative effect on FWE. Furthermore, the quality and individual weight of the metazooplankton will be reduced, with possible negative effects on higher trophic levels.

Application of molecular techniques on heterotrophic hydrogen production research

This paper reviews the application of molecular techniques in heterotrophic hydrogen production studies. Commonly used molecular techniques are introduced briefly first, including cloning-sequencing after polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE), terminal-restriction fragment length polymorphism (T-RFLP), fluorescence in situ hybridization (FISH) and quantitative real-time PCR. Application of the molecular techniques in heterotrophic hydrogen production studies are discussed in details, focusing on identification of new isolates for hydrogen production, characterization of microbial compositions in bioreactors, monitoring microbial diversity variation, visualization of microbial distribution in hydrogen-producing granular sludge, and quantification of various microbial populations. Some significant findings in recent hydrogen production studies with the application of molecular techniques are discussed, followed by a research outlook of the heterotrophic biohydrogen field.

Spatial patterns of bacterial richness and evenness in the NW Mediterranean Sea explored by pyrosequencing of the 16S rRNA

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 61:221-233 (2010) - DOI: https://doi.org/10.3354/ame01484 AME Special 4: Progress and perspectives in aquatic microbial ecology: Highlights of the SAME 11, Piran, Slovenia, 2009 Spatial patterns of bacterial richness and evenness in the NW Mediterranean Sea explored by pyrosequencing of the 16S rRNA Thomas Pommier1,2, P. R. Neal3, Josep M. Gasol1, Montserrat Coll1, Silvia G. Acinas1, Carlos Pedrós-Alió1,* 1Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar, CSIC, 08003 Barcelona, Spain 2Ecologie Microbienne, UMR5557, USC1193 CNRS, INRA, Université Lyon I, 69622 Villeurbanne, France 3Marine Biological Laboratory, Woods Hole, 02543 Massachusetts, USA *Corresponding author. Email: cpedros@icm.csic.es ABSTRACT: Due to analytical limitations, patterns of richness and evenness of microbes are scarce in the current literature. The newest and powerful pyrosequencing technology may solve this issue by sampling thousands of sequences from the same community. We conducted a study of diversity along a horizontal transect (ca. 120 km) and a depth profile (surface to bottom at ca. 2000 m) in the northwestern Mediterranean Sea, using this technology on the V6 region of the 16S rDNA gene and analyzed patterns of richness and evenness of marine free-living bacterial communities. A total of 201605 tag sequences were obtained from the 10 samples considered and clustered according to their similarity in 1200 operational taxonomic units (OTUs) per sample on average. We found a parallel decrease in richness and evenness from coast to offshore and from bottom to surface. We also observed a predominance of a few OTUs in each sample, while ca. 50% of all OTUs were found as singletons, which indicated that the community structures differed dramatically between sites despite the relative proximity and the physical connectivity between the samples. Despite these differences, using the 300 most abundant OTUs only was sufficient to obtain the same clustering of samples as with the complete dataset. Finally, both richness and evenness were negatively correlated with bacterial biomass and heterotrophic production. KEY WORDS: Bacterial diversity · Pyrosequencing · Blanes Bay Microbial Observatory Full text in pdf format PreviousNextCite this article as: Pommier T, Neal PR, Gasol JM, Coll M, Acinas SG, Pedrós-Alió C (2010) Spatial patterns of bacterial richness and evenness in the NW Mediterranean Sea explored by pyrosequencing of the 16S rRNA. Aquat Microb Ecol 61:221-233. https://doi.org/10.3354/ame01484 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 61, No. 3. Online publication date: December 30, 2010 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2010 Inter-Research.

Marine bacterioplankton biomass, activity and community structure in the vicinity of Antarctic icebergs

We studied marine bacterioplankton in the Scotia Sea in June 2008 and in the northwest Weddell Sea in March to mid April 2009 in waters proximal to three free-drifting icebergs (SS-1, A-43k, and C-18a), in a region with a high density of smaller icebergs (iceberg alley), and at stations that were upstream of the iceberg trajectories designated as far-field reference sites that were between 16-75 km away. Hydrographic parameters were used to define water masses in which comparisons between bacterioplankton-associated characteristics (abundance, leucine incorporation into protein, aminopeptidase activities and community structure) within and between water masses could be made. Early winter Scotia Sea bacterioplankton had low levels of cells and low heterotrophic production rates in the upper 50 m. Influences of the icebergs on bacterioplankton at this time of year were minimal, if not deleterious, as we found lower levels of heterotrophic production near A-43k in comparison to stations >16 km away. Additionally, the results point to small but significant differences in cell abundance, heterotrophic production, and community structure between the two icebergs studied. These icebergs differed greatly in size and the findings suggest that the larger iceberg had a greater effect. In the NW Weddell Sea in March–mid April bacterioplankton were twice as abundant and had heterotrophic productions rates that were 8-fold higher than what we determined in the Scotia Sea, though levels were still quite low, which is typical for autumn. We did not detect direct iceberg-related influences on the bacterioplankton characteristics studied here. Clues to understanding bacterioplankton responses may lie in the details of community structure, as there were some significant differences in community structure in the winter water and underlying upper circumpolar deep-water masses between stations occupied close to C-18a and at stations 18 km away (i.e. Polaribacter and Pelagibacter-related 16S rRNA gene fragments were at low levels at the 18 km stations), though higher resolution, high throughput profiling tools will be needed to pinpoint specific organisms and ecological types. Likewise, a better understanding of local to regional scale structure of bacterioplankton communities is necessary. The relationship between bacterioplankton abundance and heterotrophic production suggested bottom up processes were controlling bacterioplankton during March – mid-April in the NW Weddell Sea, and that variation in temperature may play a role in substrate utilization. Trophic linkages seen between phytoplankton and zooplankton were mirrored by tight coupling between primary production and heterotrophic production in the waters immediately surrounding C-18a and in iceberg alley (but not at stations 18 and 75 km away), suggesting that indirect effects on bacterioplankton may also be important. Overall, the results show that bacterioplankton, dominated by Rhodobacteracae Pelagibacter, and uncultivated Gammaproteobacteria groups were minimally influenced by icebergs in the regions and seasons studied here – at least directly – though further work addressing different scales, sizes of icebergs, and seasons is needed to better understand bacterioplankton-associated ecological processes and carbon cycling in regions of high iceberg production.

Recent advances in the Mediterranean researches on zooplankton: from spatial–temporal patterns of distribution to processes oriented studies

In this review we focus on research performed by Italian scientists on pelagic communities, from microzooplankton to micronekton, mainly in the Italian Seas. We considered published data, mostly as grey literature, and unpublished ones. Firstly we describe data collected over a time span of more than 30 years, during several cruises all around the Italian peninsula on zooplankton composition and distribution. We identified rare vs. common species, which enhanced biodiversity of the pelagic ecosystem. Time series, some also very long, allowed us to describe seasonal recurrent patterns, interannual fluctuations and recent shifts driven by climatic changes. More recently Italian researches were processes oriented and we analyzed results obtained on the impact of predation of both micro- and mesozooplankton on both autotrophic and heterotrophic preys. Carbon fluxes through zooplankton components were variable in space and time, but accounted for important phytoplankton losses, and when this resource became scarce they relied on heterotrophic production. Through respiration measurements of mesozooplankton another aspect of the C flux was estimated showing an increase in C demand in the most oligotrophic area. Egg production by copepods appeared to be mostly controlled by temperature and quantity/quality of available food.

Impact of lower salinity waters on bacterial heterotrophic production and community structure in the offshore NW Mediterranean Sea

We investigated the impact of water masses originating from freshwater input on bacterial heterotrophic metabolism and community structure at an offshore site in the oligotrophic NW Mediterranean Sea in 2007 and 2008. By combining 16S rRNA gene clone libraries and MICRO-CARD-FISH we determined the dominant operational taxonomic units (OTU) and their contribution to bulk abundance and activity in the presence of buoyant water masses characterized by lower salinity (LSW, < 37.9) and compared these with the winter and spring phytoplankton blooms. We demonstrate that organic matter associated with LSW markedly stimulated bacterial heterotrophic production as determined by [(3) H]-leucine incorporation. The OTUs SAR11-IA, SAR11-IIB, SAR86-I and SAR86-III were dominant in all clone libraries, while the Roseobacter clade and the Bacteroidetes OTU NorSea72 were more specific to the spring phytoplankton bloom. The relative contribution of these OTUs to leucine incorporation varied between 23% and 69% for SAR11, 2% and 17% for Roseobacter and was up to 4% for NorSea72. Together, they accounted for roughly 50% of bulk abundance and leucine incorporation during the four situations investigated. Our results suggest that a few cosmopolitan OTUs respond to different DOM sources in the NW Mediterranean Sea.

Development of the Bacterial Compartment Along the Danube River: a Continuum Despite Local Influences

Microbial food webs dominate heterotrophic food webs in large rivers with bacterial metabolism being a key component of carbon processing. Thus, analysis of bacterial population dynamics is critical to understanding patterns and mechanisms of material cycling and energy fluxes in large rivers. Within the frame of the Joint Danube Survey (JDS) 2007, the longitudinal development of the natural bacterial community in the Danube in terms of bacterial numbers, morphotype composition, and heterotrophic production of the suspended and particle-attached fractions was followed at a fine spatial resolution of approximately 30 km for the first time in such a large river along a 2,600-km stretch. Twenty-one major tributaries and branches were also included. This allowed us to investigate whether bacterial standing stock and production undergo continuous, linear changes or whether discontinuities and local processes like the merging of tributaries or the potential impact of sewage input drive the bacterial population in the Danube. The presented investigation revealed surprising continuous patterns of changes of bacterial parameters along the Danube River. Despite the presence of impoundments or hydropower plants, large municipalities, and the discharge of large tributaries, most bacterial parameters (standing stock, morphotype succession, and attached bacterial production) developed gradually, indicating that mainly broad-scale drivers and not local conditions shape and control the bacterial community in the midstream of this large river. As most important broad-scale drivers, nutrients (inorganic and organic) and changes in particle concentrations were identified. These data are also in remarkable accordance with the patterns of changes of the genetic bacterial community composition, observed during the first JDS (2001) 6 years before. In contrast, bacterial activity did not follow a continuous trend and was mainly controlled by the input of sewage from large cities in the middle section, leading to a bloom of phytoplankton. The observed patterns and the comparison between the Danube, its tributaries and other large rivers worldwide indicate that the bacterial community in rivers has a powerful indicator function for estimating the ecological status of large river ecosystems once enough information has been collected at various temporal and spatial scales.

Composition, production, and loss of carbohydrates in subtropical shallow subtidal sandy sediments: Rapid processing and long‐term retention revealed by 13C‐labeling

The composition and production of carbohydrates (mannose, rhamnose, fucose, galactose, glucose, and xylose) and their transfer among sediment compartments (microphytobenthos [MPB], bacteria, and detritus) was investigated through in situ labeling with 13C‐bicarbonate. After 60 h, 13C was found in all sediment compartments, demonstrating rapid transfer of fixed carbon from autotrophs to heterotrophs. Carbohydrates were a major carbon reservoir, accounting for 30% (day 0) to 15% (day 30) of the 13C within sediments, and probably played a role in this transfer. Carbohydrate fractions were highly reactive (65‐87%), less reactive (7‐ 18%), and nonreactive (6‐23%) over the experimental period. The rate of loss of the less reactive fraction (0.01‐ 0.05 d−1) was at least an order of magnitude lower than that for the highly reactive fraction (0.8‐4.4 d−1). Patterns of diagenesis estimated from label uptake and loss matched the carbohydrate composition observed in the sediment (glucose &gt; galactose &gt; rhamnose &gt; fucose &gt; xylose &gt; mannose) and were similar to patterns reported previously. C:N ratios and δ13C of sediment organic matter indicated an algal origin (MPB and phytoplankton). Although carbon was rapidly processed, loss from sediments was not immediate, and there was evidence of recycling into MPB and bacteria. Rapid transfer of carbon to and from carbohydrates has been found in various environments, including temperate, muddy, and intertidal sediments, and this study demonstrates the important role of carbohydrates in supporting heterotrophic production over extended periods (&gt; 30 d) in subtropical shallow subtidal sands.

Lytic failure in cross-inoculation assays between phages and prokaryotes from three aquatic sites of contrasting salinity

Little is known about the ability of phages to successfully colonize contrasting aquatic niches. We conducted experimental cross-infections between viruses and prokaryotes from three tropical sites of West Africa, with distinct salinities: a freshwater reservoir, a marine coastal station and a hypersaline lake. A cellular poison-based method (potassium cyanide) revealed that the addition of native viruses (regardless of the water type) consistently stimulated viral production. Conversely, in all incubations conducted with allochtonous (non-native) viruses, their overall production was not promoted, which suggests a lytic failure. Prokaryotic heterotrophic production increased in fresh and marine water supplemented with native viruses, but not in the hypersaline water. These results point to the role of the viral shunt in low-salinity environments, where the release of bioavailable lysis products might be of high nutritional value for the noninfected prokaryotes. In contrast, in hypersaline water where glycerol is a major carbon and energy source for the heterotrophic community, dissolved organic matter (DOM) of lytic origin may represent a less important DOM source for prokaryotes. Finally, our results suggest that cosmopolitan phages capable of moving between biomes are probably rare in aquatic habitats, supporting the common idea that most wild phages are relatively limited in their host range.

Effects of seawater acidification by ocean CO2 sequestration on bathypelagic prokaryote activities

We investigated the effects of seawater acidification induced by ocean CO2 sequestration on bathypelagic prokaryotes. We simulated acidification conditions by bubbling high-CO2 air or adding chemical buffer solutions to seawater samples in order to examine changes in total cell counts, heterotrophic production rate, direct viable cell count, and relative abundance of Bacteria and Archaea. Considerable suppression of prokaryotic activities was observed at pH 7.0 or lower, especially in samples enriched with organic matter. The relative abundance of Archaea increased with increasing CO2 concentration. We found that seawater acidification can potentially alter heterotrophic activities and community structure of bathypelagic prokaryotes.

High bicarbonate assimilation in the dark by Arctic bacteria

Although both autotrophic and heterotrophic microorganisms incorporate CO₂ in the dark through different metabolic pathways, this process has usually been disregarded in oxic marine environments. We studied the significance and mediators of dark bicarbonate assimilation in dilution cultures inoculated with winter Arctic seawater. At stationary phase, bicarbonate incorporation rates were high (0.5-2.5 μg C L⁻¹ d⁻¹) and correlated with rates of bacterial heterotrophic production, suggesting that most of the incorporation was due to heterotrophs. Accordingly, very few typically chemoautotrophic bacteria were detected by 16S rRNA gene cloning. The genetic analysis of the biotin carboxylase gene accC putatively involved in archaeal CO₂ fixation did not yield any archaeal sequence, but amplified a variety of bacterial carboxylases involved in fatty acids biosynthesis, anaplerotic pathways and leucine catabolism. Gammaproteobacteria dominated the seawater cultures (40-70% of cell counts), followed by Betaproteobacteria and Flavobacteria as shown by catalyzed reporter deposition fluorescence in situ hybridization (CARDFISH). Both Beta- and Gammaproteobacteria were active in leucine and bicarbonate uptake, while Flavobacteria did not take up bicarbonate, as measured by microautoradiography combined with CARDFISH. Within Gammaproteobacteria, Pseudoalteromonas-Colwellia and Oleispira were very active in bicarbonate uptake (ca. 30 and 70% of active cells, respectively), while the group Arctic96B-16 did not take up bicarbonate. Our results suggest that, potentially, the incorporation of CO₂ can be relevant for the metabolism of specific Arctic heterotrophic phylotypes, promoting the maintenance of their cell activity and/or longer survival under resource depleted conditions.

Prokaryotic carbon utilization in the dark ocean: growth efficiency, leucine-to-carbon conversion factors, and their relation

Experiments were conducted in the mesopelagic subtropical northeast Atlantic Ocean to determine the range of variability in the prokaryotic leucine-to-carbon conversion factor (CF), and prokaryotic growth efficiency (PGE). The way prokaryotic heterotrophic production (PHP) is calcu- lated directly influences PGE (variations of PGE between 1 and 31% were found for a single sample). The empirically obtained deep-water CFs showed a 7-fold variability (0.13 to 0.85 kg C mol -1 Leu), but were always lower than the theoretical CF of 1.55 kg C mol -1 Leu assuming no isotope dilution. Empirically determined CFs were highly correlated to PGE, suggesting that both parameters are rep- resentations of the same basic metabolic processes. Overall, the PGEs obtained in this study suggest that mesopelagic prokaryotic assemblages can sometimes be as important in carbon processing as their epipelagic counterparts.

River phosphorus cycling: Separating biotic and abiotic uptake during short-term changes in sewage effluent loading

Medium to small scale point sources continue to threaten river ecosystems through P loadings. The capacity and timescales of within-river processing and P retention are a major factor in how rivers respond to, and protect downstream ecosystems from, elevated concentrations of soluble reactive P (SRP). In this study, the bio-geochemical response of a small river (∼40 km 2 catchment area) was determined before, during and after exposure to a fourteen day pulse of treated sewage effluent using an upstream reach as a control. A wide array of approaches (batch and column simulations to in-situ whole stream metabolism) allowed independent comparison and quantification, of the relative contribution of abiotic and biotic processes in-river P cycling. This enabled, for the first time, separating the relative contributions of algae, bacteria and abiotic sorption without the use of labelled P (radioisotope). An SRP mass balance showed that the ecosystem switched from a P sink (during effluent inputs) to a P source (when effluent flow ceased). However, 65–70% of SRP was retained during the exposure time and remained sequestered two-weeks after-effluent flow ceased. Batch studies treated with biocide gave unrealistic results, but P uptake rates derived by other methods were highly comparable. Downstream of the effluent input, net P uptake by algae, bacteria and sediment (including the biofilm polysaccharide matrix) were 0.2 (±0.1), 0.4 (±0.3), and 1.0 (±0.9) mmol m −2 day −1 during effluent exposure. While autotrophic production did not respond to the effluent exposure, heterotrophic production increased by 67% relative to the control and this translated into a 50% increase in biological P uptake rate. Therefore, both biological and abiotic components of stream ecosystems uptake P during exposure to treated sewage effluent P inputs, and maintain a long ‘memory’ of this input in terms of P storage for considerable timescales after loading.

High dissolved extracellular enzymatic activity in the deep central Atlantic Ocean

The distribution of prokaryotic abundance (PA), prokaryotic heterotrophic production (PHP), and suspended particulate organic material (POM), as well as total and dissolved (operationally defined as passing through 0.2 mu m pore size filters) potential extracellular enzymatic activities (EEA; alpha- and beta-glucosidase [AGase and BGase], leucine aminopeptidase [LAPase], and alkaline phosphatase [APase]) were determined in the meso- and bathypelagic waters of the (sub)tropical Atlantic along an eastern zonal transatlantic transect and a western N-S transect. Significant differences between both transects were found for POM concentration but not for PA, PHP (except in the subsurface and oxygen minimum layer), and dissolved and total EEA. PHP decreased by 3 orders of magnitude from the lower euphotic zone to bathypelagic waters, while PA and cell-specific PHP decreased only by 1 and 2 orders of magnitude, respectively. The proportion of the dissolved to the total EEA was high in the dark ocean for all the enzymes, ranging from 54 to 100, 56 to 100, 65 to 100 and 57 to 97 % for AGase, BGase, LAPase and APase, respectively. The kinetic parameters (V-max, and K-m) of both the dissolved and total fractions of LAPase and APase were very similar throughout the water column, suggesting a similar origin for both dissolved and particulate EEA. Significant correlations of both dissolved and total EEA were found with prokaryotic metabolism and the POM pool. Based on the previous notion that the fraction of dissolved EEA is higher in particle-attached than in free-living microbes, our results suggest that microbial activity in the dark ocean occurs mainly on colloidal and particulate material. This is in agreement with recent genomic evidence. However, these colloidal and particulate materials are prone to disruption during the sampling process. Hence, more selective sampling techniques are needed to specifically collect these deep-water aggregates that probably represent hotspots of microbial activity in the deep ocean.

Investigation into Heterotrophic Activities and Algal Biomass in Surface Flow Stormwater Wetlands

Stormwater wetlands have been mainly designed in an empirical approach for water quality improvement, with little quantitative understanding of the internal microbia l processes. This study investigated into heterotrophic bacterial pro duction rate, heterotrophic bacterial mineralization percentage, and algal biomass in hypertrophic and eutrophic surface flow stormwat er wetlands. Compared to a nearby wood leachate treatment wetland, the stormwater wetlands had much higher chlorophyll-a concentrations. The eutrophic stormwater wetland had improved water quality, whereas the hypertrophic stormwater wetland had degraded water quality. Heterotrophic bacterial activities in wate r were limited in the stormwater wetlands due to competition of algal gro wth for nutrients. The relative contribution of biofilms to the overal l heterotrophic activities was higher in the stormwater wetlands th an that in the wood leachate treatment wetland. Keywords—chlorophyll-a, constructed wetland, heterotrophic production, mineralization, stormwater

Viral decay and viral production rates in continental-shelf and deep-sea sediments of the Mediterranean Sea

Here, for the first time, we have carried out synoptic measurements of viral production and decay rates in continental-shelf and deep-sea sediments of the Mediterranean Sea to explore the viral balance. The net viral production and decay rates (1.1-61.2 and 0.6-13.5 x 10(7) viruses g(-1) h(-1), respectively) were significantly correlated, and were also related to prokaryotic heterotrophic production. The addition of enzymes increased the decay rates in the surface sediments, but not in the subsurface sediments. Both the viral production and the decay rates decreased significantly in the deeper sediment layers, while the virus-to-prokaryote abundance ratio increased, suggesting a high preservation of viruses in the subsurface sediments. Viral decay did not balance viral production at any of the sites investigated, accounting on average for c. 32% of the gross viral production in the marine sediments. We estimate that the carbon (C) released by viral decay contributed 6-23% to the total C released by the viral shunt. Because only c. 2% of the viruses produced can infect other prokaryotes, the majority is not subjected to direct lysis and potentially remains as a food source for benthic consumers. The results reported here suggest that viral decay can play an important role in biogeochemical cycles and benthic trophodynamics.

Selected pioneering works on humus in soils and sediments during the 20th century: A retrospective look from the International Humic Substances Society view

Organic matter in general, and humic substances (HS) in particular, are involved in many processes in soils, sediments, rocks and natural waters. These include rock weathering, plant nutrition, pH buffering, trace metal mobility and toxicity, bioavailability, degradation and transport of hydrophobic organic chemicals, formation of disinfection by-products during water treatment, heterotrophic production in blackwater ecosystems and, more generally, the global carbon cycle. Before the 1970s, natural organic matter of different ecosystem pools ( i.e., soils, sediments, and natural waters) was often studied in isolation, although many similarities exist between them. This is particularly so for HS. In this historical context, a need appeared at the international level for bringing together environmental chemists, soil scientists, hydrologists, and geologists who were interested in HS to provide a forum for the exchange of ideas, to standardize analytical procedures and agree on definitions of HS. The International Humic Substances Society (IHSS) was founded in Denver, Colorado (USA) in 1981 with several objectives among them “to bring together scientists in the coal, soil, and water sciences with interests in humic substances” (home page of the IHSS web site: http://ihss.gatech.edu/ihss2/index.html). This paper presents selected pioneering works on humus in soils and sediments during the 20th century with a special focus on the links between the studies of soil HS and the formation, during early diagenesis, of the precursors of kerogens. Temporal coverage includes key contributions preceding the founding of the IHSS, and a brief history of the organization is presented.

Temporal changes of major bacterial groups and bacterial heterotrophic activity during a Phaeocystis globosa bloom in the eastern English Channel

The temporal changes in major bacterial groups and bulk heterotrophic activity were determined during the growth, senescence and post-bloom phases of a Phaeocystis globosa bloom, at a coastal site in the eastern English Channel. Cell-specific exoenzymatic activities were highest dur- ing the growth period of P. globosa, while bacterial abundance and bacterial heterotrophic produc- tion peaked during the senescence of the P. globosa bloom. Bacteroidetes and Gammaproteobacteria were the most important bacterial groups during the growth period of P. globosa, contributing between 13 and 47% of bulk bacterial abundance and leucine incorporation. At the end of the phyto- plankton growth period, Gammaproteobacteria were the most important contributors to bacterial heterotrophic production, accounting for 68% of bulk leucine incorporation. During the senescent phase, 36 and 29% of bulk leucine incorporation were attributable to Bacteroidetes and Alphapro- teobacteria, respectively. Finally, after the disappearance of the bloom, Gamma- and Alphapro- teobacteria dominated by the Roseobacter clade were responsible for 33 and 43% of bulk leucine incorporation, respectively. The relative abundance of the bacterial groups showed little variability between consecutive dates during most of the study period. The contributions of different bacterial groups to bulk abundance and leucine incorporation were correlated with exo-proteolytic and -glu- cosidic activities and with particulate organic carbon, suggesting at least some specificity of these bacterial groups with respect to their metabolic properties in the environment.

Structure and function of the mesopelagic microbial loop in the NW Mediterranean Sea

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 57:351-362 (2009) - DOI: https://doi.org/10.3354/ame01370 AME Special: 'Rassoulzadegan at Villefranche-sur-Mer: 3 decades of aquatic microbial ecology' Structure and function of the mesopelagic microbial loop in the NW Mediterranean Sea Tsuneo Tanaka* Aix-Marseille University, CNRS, LOPB-UMR 6535, OSU/Centre d’Océanologie de Marseille, Campus de Luminy-Case 901, 13288 Marseille Cedex 09, France *Email: tsuneo.tanaka@univmed.fr ABSTRACT: The mesopelagic layer is where the majority of the particulate organic carbon exported from the epipelagic layer is remineralized to CO2. Recent studies at the DYFAMED time-series station in the NW Mediterranean Sea have shown that dominance of prokaryotes (Bacteria and Archaea) within the microbial community represented by biomass data increases with depth. The studies have also shown that the depth-integrated biomass of protists (heterotrophic flagellates and ciliates) in the mesopelagic layer is as great as that in the epipelagic layer, and that biomass of mesopelagic prokaryotes is controlled by both substrate availability (bottom-up control) and predation and viral infection (top-down control). Data on prokaryotic growth efficiency (derived from the prokaryotic heterotrophic production and the loss of organic carbon flux in the mesopelagic layer on an annual scale) suggest that mesopelagic prokaryotes are not simply remineralizers of organic carbon, but also play an important role in supporting the production of organisms belonging to higher trophic levels. Analysis using a simple food chain model suggests that heterotrophic nanoflagellates may be important remineralizers of organic carbon produced by prokaryotes, and that the viral loop may enhance remineralization of organic carbon in the mesopelagic layer. There are, however, uncertain elements in measuring organic carbon flux and biomass and activity of the microbial components in the mesopelagic layer. By comparing the results obtained at the DYFAMED station with those obtained from other environments, this study summarizes our current knowledge on the structure and function of the mesopelagic microbial loop in the NW Mediterranean Sea as well as in other oceanic regions. KEY WORDS: Mesopelagic microbial loop · Protists · Carbon flux · NW Mediterranean Sea Full text in pdf format PreviousCite this article as: Tanaka T (2009) Structure and function of the mesopelagic microbial loop in the NW Mediterranean Sea. Aquat Microb Ecol 57:351-362. https://doi.org/10.3354/ame01370Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 57, No. 3. Online publication date: November 24, 2009 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2009 Inter-Research.

Linkage Between Bacterial Carbon Processing and the Structure of the Active Bacterial Community at a Coastal Site in the NW Mediterranean Sea

The temporal dynamics in bulk bacterial parameters and in the richness of the total and active bacterial community, determined from CE-SSCP fingerprints of 16S rRNA genes and 16S rRNA transcripts, respectively, were followed weekly to bimonthly at an oligotrophic coastal site in the NW Mediterranean Sea. Bacterial abundance, bacterial heterotrophic production, and bacterial and community respiration determined over two seasonal cycles displayed large short-term variability and no pronounced temporal pattern was detectable for these parameters. Concentrations in inorganic nutrients, salinity, or concentrations of chlorophyll a could not significantly explain the temporal variability of the bacterial parameters determined. By contrast, bacterial respiration and the bacterial carbon demand were both negatively correlated with the richness of the active bacterial community, while the bacterial parameters determined herein were not related to the richness of the total bacterial community present. Our results indicate that a reduced number of ribotypes is active when rates of bacteria-mediated carbon processes are high. Our approach, based on fingerprints of 16S rRNA transcripts, could represent an interesting tool to investigate the relationship between the structure and function of marine bacteria, in particular, on short temporal and spatial scales.