Phytoplankton Extracellular Release Research Articles

Diel investments in metabolite production and consumption in a model microbial system

Organic carbon transfer between surface ocean photosynthetic and heterotrophic microbes is a central but poorly understood process in the global carbon cycle. In a model community in which diatom extracellular release of organic molecules sustained growth of a co-cultured bacterium, we determined quantitative changes in the diatom endometabolome and the bacterial uptake transcriptome over two diel cycles. Of the nuclear magnetic resonance (NMR) peaks in the diatom endometabolites, 38% had diel patterns with noon or mid-afternoon maxima; the remaining either increased (36%) or decreased (26%) through time. Of the genes in the bacterial uptake transcriptome, 94% had a diel pattern with a noon maximum; the remaining decreased over time (6%). Eight diatom endometabolites identified with high confidence were matched to the bacterial genes mediating their utilization. Modeling of these coupled inventories with only diffusion-based phytoplankton extracellular release could not reproduce all the patterns. Addition of active release mechanisms for physiological balance and bacterial recognition significantly improved model performance. Estimates of phytoplankton extracellular release range from only a few percent to nearly half of annual net primary production. Improved understanding of the factors that influence metabolite release and consumption by surface ocean microbes will better constrain this globally significant carbon flux.

Nutrient availability as major driver of phytoplankton-derived dissolved organic matter transformation in coastal environment

Incubation experiments were performed to examine the processing of fresh autochthonous dissolved organic matter (DOM) produced by coastal plankton communities in spring and autumn. The major driver of observed DOM dynamics was the seasonally variable inorganic nutrient status and characteristics of the initial bulk DOM, whereas the characteristics of the phytoplankton community seemed to have a minor role. Net accumulation of dissolved organic carbon (DOC) during the 18-days experiments was 3.4 and 9.2 µmol l−1 d−1 in P-limited spring and N-limited autumn, respectively. Bacterial bioassays revealed that the phytoplankton-derived DOC had surprisingly low proportions of biologically labile DOC, 12.6% (spring) and 17.5% (autumn). The optical characteristics of the DOM changed throughout the experiments, demonstrating continuous heterotrophic processing of the DOM pool. However, these temporal changes in optical characteristics of the DOM pool were not the same between seasons, indicating seasonally variable environmental drivers. Nitrogen and phosphorus availability is likely the main driver of these seasonal differences, affecting both phytoplankton extracellular release of DOM and its heterotrophic degradation by bacteria. These findings underline the complexity of the DOM production and consumption by the natural planktonic community, and show the importance of the prevailing environmental conditions regulating the DOM pathways.

Local differences in phytoplankton-bacterioplankton coupling in the coastal upwelling off Galicia (NW Spain)

We simultaneously studied microbial-mediated carbon fluxes at 2 contrasting sites within the coastal upwelling system off Galicia, near A Coruna and Vigo, Spain, over an annual cycle in order to compare the fraction of primary production released as dissolved organic carbon (DOC) and the degree of coupling between bacteria and phytoplankton. A significant fraction of primary production was released as DOC at both sites, averaging ~30%. DOC release ac counted for, on average, 30% of the total bacterial carbon demand, which is indicative of a moderate trophic dependence of bacteria on phytoplankton in these coastal ecosystems. Nevertheless, dif- ferences in hydrographic conditions associated with stronger upwelling pulses off Vigo, and deeper upper mixed layers during the downwelling period off A Coruna, led to significant differ- ences in phytoplankton dynamics and the subsequent direct coupling with heterotrophic bacteria. Strong direct coupling between phytoplankton extracellular release and bacterial production (BP) was found off Vigo, which could be related to the quality of the DOC produced by actively grow- ing phytoplankton. By contrast, DOC release and BP rates were decoupled off A Coruna, likely due to unaccounted DOC associated with indirect trophic processes or to the low availability of freshly produced exudates associated with overflow or photoinhibition mechanisms.

Production of dissolved organic matter by phytoplankton and its uptake by heterotrophic prokaryotes in large tropical lakes

In pelagic ecosystems, phytoplankton extracellular release can extensively subsidize the heterotrophic prokaryotic carbon demand. Time‐course experiments were carried out to quantify primary production, phytoplankton excretion, and the microbial uptake of freshly released dissolved organic carbon (DOC) derived from phytoplankton extracellular release (DOCp) in four large tropical lakes distributed along a productivity gradient: Kivu, Edward, Albert, and Victoria. The contributions of the major heterotrophic bacterial groups to the uptake of DOCp was also analyzed in Lake Kivu, using microautoradiography coupled to catalyzed reporter deposition fluorescent in situ hybridization. The percentage of extracellular release (PER) varied across the productivity gradient, with higher values at low productivity. Furthermore, PER was significantly related to high light and low phosphate concentrations in the mixed layer and was comparatively higher in oligotrophic tropical lakes than in their temperate counterparts. Both observations suggest that environmental factors play a key role in the control of phytoplankton excretion. Standing stocks of DOCp were small and generally contributed less than 1% to the total DOC because it was rapidly assimilated by prokaryotes. In other words, there was a tight coupling between the production and the heterotrophic consumption of DOCp. None of the major phylogenetic bacterial groups that were investigated differed in their ability to take up DOCp, in contrast with earlier results reported for standard labeled single‐molecule substrates (leucine, glucose, adenosine triphosphate). It supports the idea that the metabolic ability to use DOCp is widespread among heterotrophic prokaryotes. Overall, these results highlight the importance of carbon transfer between phytoplankton and bacterioplankton in large African lakes.

Seasonal dynamics of dissolved organic matter and microbial activity in the coastal North 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 60:85-95 (2010) - DOI: https://doi.org/10.3354/ame01404 Seasonal dynamics of dissolved organic matter and microbial activity in the coastal North Sea Eva Sintes1,2,*, Karen Stoderegger1, Veronica Parada1, Gerhard J. Herndl1,2 1Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB, Den Burg, The Netherlands 2Department of Marine Biology, Faculty Center of Ecology, University of Vienna, Althanstr. 14, 1090 Vienna, Austria *Email: eva.sintes@univie.ac.at ABSTRACT: The dynamics of dissolved organic matter (DOM) and microbial activity were monitored in the coastal North Sea over an annual cycle. DOM accumulated during the spring bloom towards the summer, associated with high phytoplankton extracellular release. Accumulation of dissolved organic carbon (DOC) occurred from April to June. During this period, based on the bacterial carbon demand (BCD) of the free-living bacteria and the photosynthetic extracellular release (PER), 85 µM C were derived from sources other than direct DOC release by phytoplankton. Thereafter, from the end of August until December, the DOM concentrations decreased by about half. During this period, at least 269 µM C was removed from the system via the utilization by the bacterial community and/or sedimentation and export. Overall, our data indicate a pronounced seasonal shift in DOM sources supporting BCD. From spring to summer, BCD is almost fully supported by PER alone while in fall and winter, BCD is supported about equally by PER and by the DOM accumulated in the spring–summer period and originating presumably from a variety of DOM production mechanisms. KEY WORDS: Bacterial activity · Dissolved organic matter · Production · Consumption · North Sea Full text in pdf format PreviousNextCite this article as: Sintes E, Stoderegger K, Parada V, Herndl GJ (2010) Seasonal dynamics of dissolved organic matter and microbial activity in the coastal North Sea. Aquat Microb Ecol 60:85-95. https://doi.org/10.3354/ame01404 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 60, No. 1. Online publication date: May 04, 2010 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2010 Inter-Research.

Linkages between bacterioplankton community composition, heterotrophic carbon cycling and environmental conditions in a highly dynamic coastal ecosystem

We used mesocosm experiments to study the bacterioplankton community in a highly dynamic coastal ecosystem during four contrasting periods of the seasonal cycle: winter mixing, spring phytoplankton bloom, summer stratification and autumn upwelling. A correlation approach was used in order to measure the degree of coupling between the dynamics of major bacterial groups, heterotrophic carbon cycling and environmental factors. We used catalysed reporter deposition-fluorescence in situ hybridization to follow changes in the relative abundance of the most abundant groups of bacteria (Alphaproteobacteria, Gammaproteobacteria and Bacteroidetes). Bacterial carbon flux-related variables included bacterial standing stock, bacterial production and microbial respiration. The environmental factors included both, biotic variables such as chlorophyll-a concentration, primary production, phytoplankton extracellular release, and abiotic variables such as the concentration of dissolved inorganic and organic nutrients. Rapid shifts in the dominant bacterial groups occurred associated to environmental changes and bacterial bulk functions. An alternation between Alphaproteobacteria and Bacteroidetes was observed associated to different phytoplankton growth phases. The dominance of the group Bacteroidetes was related to high bacterial biomass and production. We found a significant, non-spurious, linkage between the relative abundances of major bacterial groups and bacterial carbon cycling. Our results suggest that bacteria belonging to these major groups could actually share a function in planktonic ecosystems.

Bacterial dissolved organic carbon demand in McMurdo Dry Valley lakes, Antarctica

The proximal substrate source of planktonic bacteria is dissolved organic carbon (DOC), and the combined sources of DOC (bulk, phytoplankton production, and advected) set an upper limit on how much C is available for bacterial respiration (BR). We compared measurements of bacterial production (BP) and estimates of BR to measurements of what we assumed to be the major DOC inputs for three permanently iceߚcovered lakes in Antarctica: Lakes Fryxell, Hoare, and Bonney. These measured inputs, which included phytoplankton extracellular release (ECR), stream input, and upward diffusion of DOC across the chemocline, sediments, and benthic microbial mats, were three to eight times smaller than planktonic BR, suggesting that a major source of bacterial C was unaccounted for. Despite overestimating DOC and doubling bacterial growth efficiency (BGE), BR in the lakes was 1.25ߚ2 times greater than our estimate of DOC supply. We hypothesize that a major source of organic C for planktonic bacteria in these lakes comes from drawdown of bulk DOC and/or decomposition of particulate material.

Microbial loop carbon cycling in ocean environments studied using a simple steady-state model

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 26:37-49 (2001) - doi:10.3354/ame026037 Microbial loop carbon cycling in ocean environments studied using a simple steady-state model Thomas R. Anderson1,*, Hugh W. Ducklow2 1Southampton Oceanography Centre, Waterfront Campus, European Way, Southampton SO14 3ZH, United Kingdom 2College of William and Mary School of Marine Science, Rte 1208, Box 1346, Gloucester Point, Virginia 23062, USA *E-mail: tra@soc.soton.ac.uk ABSTRACT: A simple steady-state model is used to examine the microbial loop as a pathway for organic C in marine systems, constrained by observed estimates of bacterial to primary production ratio (BP:PP) and bacterial growth efficiency (BGE). Carbon sources (primary production including extracellular release of dissolved organic carbon, DOC), cycling via zooplankton grazing and viral lysis, and sinks (bacterial and zooplankton respiration) are represented. Model solutions indicate that, at least under near steady-state conditions, recent estimates of BP:PP of about 0.1 to 0.15 are consistent with reasonable scenarios of C cycling (low BGE and phytoplankton extracellular release) at open ocean sites such as the Sargasso Sea and subarctic North Pacific. The finding that bacteria are a major (50%) sink for primary production is shown to be consistent with the best estimates of BGE and dissolved organic matter (DOM) production by zooplankton and phytoplankton. Zooplankton-related processes are predicted to provide the greatest supply of DOC for bacterial consumption. The bacterial contribution to C flow in the microbial loop, via bacterivory and viral lysis, is generally low, as a consequence of low BGE. Both BP and BGE are hard to quantify accurately. By indicating acceptable combinations of parameter values for given BP:PP, the model provides a simple tool for examining the reliability of BP and BGE estimates. KEY WORDS: Microbial loop · Bacterial production · BGE · Models · DOC · Extracellular release Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 26, No. 1. Online publication date: October 26, 2001 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2001 Inter-Research.

Role of ultraviolet radiation on phytoplankton extracellular release and its subsequent utilization by marine bacterioplankton

The influence of ultraviolet (UV) radiation on the production rate and percentage of photosynthetic extracellular release (PER) to total production (PER + particulate) was investigated in the laboratory using the diatom species Chaetoceros muelleri grown under different nutrient and radiation conditions. Only when growing on higher nutrient concentrations (f/2 and f/4 media), were both specific particulate production and PER rates (production per unit chl a) were significantly lower in the presence of photosynthetic active radiation (PhAR) + UV as compared to the treatments receiving only PhAR. When growing on lower nutrient concentrations (f/16 medium), UV radiation had no sigmficant effect on the production rates. The percentage of PER to the total amount of carbon fixed was sirmlar for the PhAR + UV and the PhAR treatments. However, PER produced by C. muelleri during PhAR + UV exposure was taken up by bacterioplankton in the dark at significantly lower rates than PER produced in the absence of UV. This indicates that PER, considered as an important component of the dissolved organic carbon pool, becomes more resistant to bacterial utilization upon UV exposure. Whether this reduced PER-uptake by bacterioplankton is caused by changes in the macromolecular composition of the PER and/or is due to a subsequent photochemically induced alteration of the molecules during UV-exposure remains to be investigated.

Phytoplankton extracellular release and bacterial growth: dependence on the inorganic N: P ratio

Batch cultures of Chaetoceros affinis grown under nitrogen- (N:P = 5) and phosphorus- (N:P = 100) limited conditions exhibited 30 and 100% higher rates of photosynthetic extracellular release (PER), respectively, than C affims grown under balanced nutrient conditions (N.P = 16). Inoculations of natural bacterial assemblages to PER derived from phytoplankton grown under these different nutrient regimes exhibited highest potential bacterial growth yields (- 46 %) on PER derived from balanced growth. Analysis of the dissolved monomeric (MCHO) and polymeric (PCHO) carbo- hydrate pool and of the dissolved free amino acid (DFAA) fraction of the PER indicated significantly higher specific release rates of these components for phytoplankton grown under P limitation Based on the fluctuation of the MCHO, PCHO and DFAA pool in the batch cultures and on bacterial extra- cellular enzymatic activity (EEA) and bacterial growth yield we have evidence that under P-limited conditions bacteria are not taking up the available carbon efficiently. Bacteria growing on PER derived from N-lmted conditions exhibited high bacterial a- and p-glucosidase activity, while under P limta- tion low EEA was detectable. Extrapolating our results to the severely P-limited summer conditions of the Northern Adriatic Sea, we might conclude that P limitation provokes elevated PER m exponentially growing phytoplankton which is not utilized efficiently by the natural bacterial consortia. This would allow the PER to coagulate and eventually form mucilage.

Bacterial biomass, heterotrophic production and utilization of dissolved organic matter photosynthetically produced in the Almeria-Oran front

Bacterial biomass, bacterial production and the quantitative importance of the heterotrophic assimilation of photosynthetically produced dissolved organic carbon (PDOC) were examined in relation to the hydrodynamical and biological conditions in the Almeria-Oran front area (Alboran Sea, Western Mediterranean). Although, including all data, bacterial abundance correlated with chlorophyll a ( r = 0.49), the bacteria/phytoplankton carbon ratio decreased in the core of the Atlantic jet. Bacterial integrated secondary production ranged from 124 to 199 mg C m −2 d −1. Bacterial generation times averaged 3.2 d (S.D.= 1.3) in frontal sites above the pycnocline and 25 d (S.D. = 11) under the pycnocline. In the adjacent Mediterranean waters, bacterial generation times displayed homogenous values from the surface to 150 m (mean 2.7;d; S.D. = 1.5). An isolated Atlantic water mass, at the right side of the jet, showed the longest average bacterial generation times (9.5 d). In the chlorophyll maximum layers, percent extracellular release represented 23.5% of total net primary production in the oligotrophic sites and only 6.5% in the core of the Atlantic jet. The contribution of PDOC to bacterial production exhibited large variations (17–100%). Dissimilarities among sites and hydrodynamical structures of the water masses were mostly observed in bacterial generation times and phytoplankton extracellular release.

Qualitative importance of the microbial loop and plankton community structure in a eutrophic lake during a bloom of cyanobacteria

Plankton community structure and major pools and fluxes of carbon were observed before and after culmination of a bloom of cyanobacteria in eutrophic Frederiksborg Slotssø, Denmark. Biomass changes of heterotrophic nanoflagellates, ciliates, microzooplankton (50 to 140 μm), and macrozooplankton (larger than 140 μm) were compared to phytoplankton and bacterial production as well as micro- and macrozooplankton ingestion rates of phytoplankton and bacteria. The carbon budget was used as a means to examine causal relationships in the plankton community. Phytoplankton biomass decreased and algae smaller than 20 μm replacedAphanizomenon after the culmination of cyanobacteria. Bacterial net production peaked shortly after the culmination of the bloom (510 μg C liter(-1) d(-1) and decreased thereafter to a level of approximately 124 μg C liter(-1) d(-1). Phytoplankton extracellular release of organic carbon accounted for only 4-9% of bacterial carbon demand. Cyclopoid copepods and small-sized cladocerans started to grow after the culmination, but food limitation probably controlled the biomass after the collapse of the bloom. Grazing of micro- and macrozooplankton were estimated from in situ experiments using labeled bacteria and algae. Macrozooplankton grazed 22% of bacterial net production during the bloom and 86% after the bloom, while microzooplankton (nauplii, rotifers and ciliates larger than 50 μm) ingested low amounts of bacteria and removed 10-16% of bacterial carbon. Both macro-and microzooplankton grazed algae smaller than 20 μm, although they did not control algal biomass. From calculated clearance rates it was found that heterotrophic nanoflagellates (40-440 ml(-1)) grazed 3-4% of the bacterial production, while ciliates smaller than 50 μm removed 19-39% of bacterial production, supporting the idea that ciliates are an important link between bacteria and higher trophic levels. During and after the bloom ofAphanizomenon, major fluxes of carbon between bacteria, ciliates and crustaceans were observed, and heterotrophic nanoflagellates played a minor role in the pelagic food web.

Factors affecting phytoplankton extracellular release in the Southern Bight of the North Sea

Phytoplankton extra cellular release of organic substances was studied in the Southern Bight of the North Sea in relation to changes in growth conditions (light intensity and inorganic nitrogen concentration) and in taxonomie phytoplankton composition. Light intensity had no effect on percent extracellular release (PER). A high negative correlation between PER and mineraI nitrogen concentration was found during spring bloom wh en phytoplankton were dominated by flagellates (Phaeocystis poucheti in the Southern Bight; dinoflagellates in the oligotrophic English Channel). The physiological response of the flagellate.populations to shortage of nutrients differed. High PER was measured during the decline of the bloom with lower values in oligotrophic (46 %) than eutrophie waters (70 to 80 %). On the other hand, no significant correlation was found between PER and mineraI nitrogen for diatoms which dominate the phytoplankton population outside the spring period. PER values were unchangeably low (0 to 14 %) over a large range of mineraI nitrogen concentrations (0 to 50 µg at N 1-1).

Factors affecting phytoplankton extracellular release in the Southern Bight of the North Sea

Factors affecting phytoplankton extracellular release in the Southern Bight of the North Sea

Seasonal variations in the production and consumption of amino acids by coastal microplankton

A seasonal study on coastal microplankton was conducted in surface waters near Boothbay Harbor, Maine. Phytoplankton biomass, particulate production and extracellular organic release were examined in conjunction with microheterotrophic biomass and the uptake and respiration of amino acids. In situ dissolved free amino acid (DFAA) concentrations were also determined. Several phytoplankton blooms occurred throughout the year, in mid-summer, late autumn and in mid-winter. Heterotrophic activity and biomass paralleled phytoplankton extracellular release more closely than either phytoplankton particulate production or biomass. DFAA concentrations were not wholly dependent on extracellular release. Heterotrophic uptake did not appear to be dependent on DFAA concentrations but rather on rates of production of DOC by phytoplankton.

Gross Excretion Rates of Natural Marine Phytoplankton and Heterotrophic Uptake of Excreted Products in the Southern North Sea, as Determined by Short-Term Kinetics

Phytoplankton extracellular production has been determined kinetically during the spring phytoplankton bloom in three marine biotopes representative of the Southern North Sea (Scheldt estuary, Belgian coast and English Channel), differing greatly in their biological activities. Short-term kinetics of phytoplankton extracellular compounds produced during 14C incubations have been shown to increase our present capability for estimating gross phytoplankton extracellular production, if compared with a single measure after 4 h incubation. Underestimates of up to 60%;, were found when a fixed incubation of 4 h was used. This underestimate can be attributed either to heterotrophic uptake of excreted products or to the presence of a lag¬phase in 14C extra cellular compounds production, related to physiological properties of phytoplankton. The data indicate that the phytoplankton extracellular release percentage, expressed with respect to the total photo-assimilated carbon, ranges from 0 to 62% with lower values in the estuarine area. Seasonal variations show, in Belgian waters and in the English Channel, an increase in phytoplankton excretion percentage during the bloom from about 20 to 60%. Heterotrophic uptake of phytoplankton extracellular products has been calculated from the evolution curve of 14C phytoplankton excretion products by me ans of a simple mathematical model. Results indicate that heterotrophs can occasionally remove up to 39% of the total amount of excreted matter per hour indicating that phytoplankton excretion can sometimes produce substances with high turnover.

Phytoplankton extracellular release and its relation to the seasonal cycle of dissolved organic carbon in a eutrophic lake 1

The concentration of total dissolved organic carbon (TDOC), the daily rates of release of extracellular dissolved organic carbon (DOC) by viable phytoplankton, and the daily rates of assimilation of the phytoplankton extracellular DOC by bacteria were investigated simultaneously from April through October in Frains Lake, Michigan. The concentration of TDOC varied aperiodically. The release of DOC by phytoplankton and its utilization by bacteria fluctuated markedly, but these processes did not play a significant role in causing the seasonal variations of TDOC. Increases in the concentration of TDOC greatly exceeded the amounts accumulated from release by the phytoplankton, even when maximum rates of phytoplankton DOC release were calculated by assuming release exclusively from a large intracellular pool not at isotopic equilibrium. In addition, bacterial utilization of the phytoplankton DOC alone could not account for decreases in TDOC concentration. Therefore, there must be other major sources of dissolved organic matter than that provided by the mechanism of extracellular release by phytoplankton. The littoral flora and the decomposition of dead particulate organic materials are the most likely sources of fluctuations of TDOC in Frains Lake.