Disentangling microbial networks across pelagic zones in the tropical and subtropical global ocean.

Microbial interactions are vital in maintaining ocean ecosystem function, yet their dynamic nature and complexity remain largely unexplored. Here, we use association networks to investigate possible ecological interactions in the marine microbiome among archaea, bacteria, and picoeukaryotes throughout different depths and geographical regions of the tropical and subtropical global ocean. Our findings reveal that potential microbial interactions change with depth and geographical scale, exhibiting highly heterogeneous distributions. A few potential interactions were global, meaning they occurred across regions at the same depth, while 11-36% were regional within specific depths. The bathypelagic zone had the lowest proportion of global associations, and regional associations increased with depth. Moreover, we observed that most surface water associations do not persist in deeper ocean layers despite microbial vertical dispersal. Our work contributes to a deeper understanding of the tropical and subtropical global ocean interactome, which is essential for addressing the challenges posed by global change.

Global biogeography of the smallest plankton across ocean depths.

Tiny ocean plankton (picoplankton) are fundamental for the functioning of the biosphere, but the ecological mechanisms shaping their biogeography were partially understood. Comprehending whether these microorganisms are structured by niche versus neutral processes is relevant in the context of global change. We investigate the ecological processes (selection, dispersal, and drift) structuring global-ocean picoplanktonic communities inhabiting the epipelagic (0 to 200 meters), mesopelagic (200 to 1000 meters), and bathypelagic (1000 to 4000 meters) zones. We found that selection decreased, while dispersal limitation increased with depth, possibly due to differences in habitat heterogeneity and dispersal barriers such as water masses and bottom topography. Picoplankton ß-diversity positively correlated with environmental heterogeneity and water mass variability, but this relationship tended to be weaker for eukaryotes than for prokaryotes. Community patterns were more pronounced in the Mediterranean Sea, probably because of its cross-basin environmental heterogeneity and deep-water isolation. We conclude that different combinations of ecological mechanisms shape the biogeography of the ocean microbiome across depths.

Phytoplankton responses to changing temperature and nutrient availability are consistent across the tropical and subtropical Atlantic.

Temperature and nutrient supply interactively control phytoplankton growth and productivity, yet the role of these drivers together still has not been determined experimentally over large spatial scales in the oligotrophic ocean. We conducted four microcosm experiments in the tropical and subtropical Atlantic (29°N-27°S) in which surface plankton assemblages were exposed to all combinations of three temperatures (in situ, 3 °C warming and 3 °C cooling) and two nutrient treatments (unamended and enrichment with nitrogen and phosphorus). We found that chlorophyll a concentration and the biomass of picophytoplankton consistently increase in response to nutrient addition, whereas changes in temperature have a smaller and more variable effect. Nutrient enrichment leads to increased picoeukaryote abundance, depressed Prochlorococcus abundance, and increased contribution of small nanophytoplankton to total biomass. Warming and nutrient addition synergistically stimulate light-harvesting capacity, and accordingly the largest biomass response is observed in the warmed, nutrient-enriched treatment at the warmest and least oligotrophic location (12.7°N). While moderate nutrient increases have a much larger impact than varying temperature upon the growth and community structure of tropical phytoplankton, ocean warming may increase their ability to exploit events of enhanced nutrient availability.

Clinical characteristics, health care resource utilization and direct medical costs of Rotavirus hospitalizations in Spain (2013-2018).

Rotavirus (RV) is the most common cause of severe gastroenteritis (GE) in infants and young children worldwide and is associated with a significant clinical and economic burden. The objective of this study was to analyze the characteristics, healthcare resource utilization and the direct medical costs related to RVGE hospitalizations in Spain. An observational, multicenter, cross-sectional study was conducted from June 2013 to May 2018 at the pediatric departments of 12 hospitals from different Spanish regions. Children under 5 years of age admitted to the hospital with a confirmed diagnosis of RVGE were selected. Data on clinical characteristics, healthcare resource use and costs were collected from patient records and hospital databases. Most children hospitalized for RVGE did not have any previous medical condition or chronic disease. Forty-seven percent had previously visited the Emergency Room (ER), 27% had visited a primary care pediatrician, and 15% had received pharmacological treatment prior to hospital admission due to an RVGE episode. The average length of a hospital stay for RVGE was 5.6 days, and the mean medical costs of RVGE hospitalizations per episode ranged from 3,940€ to 4,100€. The highest direct medical cost was due to the hospital stay. This study showed a high burden of health resource utilization and costs related to the management of cases of RVGE requiring hospitalization. RV vaccination with high coverage rates should be considered to minimize the clinical and economic impacts of this disease on the health-care system.

Untreated sewage outfalls do not promote Trichodesmium blooms in the coasts of the Canary Islands.

During the summer of 2017, recurrent extensive blooms of the diazotrophic cyanobacterium Trichodesmium invaded the beaches and coastal waters of the Canary Islands, causing great social alarm. Some local media and public sectors ascribed, without any strong scientific evidence, the origin and reactivation of these blooms to untreated sewage outfalls distributed along the coasts. In order to test whether sewage outfalls could have any influence on the metabolic activity of Trichodesmium, we performed 13C and 15N2 uptake experiments with colonies experiencing three different bloom development stages, incubated both with clear seawater and sewage water from an outfall south of Gran Canaria island. Our results showed that sewage outfalls did not promote any increase in dinitrogen (N2) fixation in Trichodesmium, supporting the hypothesis that decaying blooms were generated offshore and transported shoreward by local currents and winds, accumulating mostly leeward of the islands. The combination of unusually warm seawater temperatures, enhanced and sustained stratification of the upper water column and recurrent dust deposition events would have favored the development of the Trichodesmium blooms, which lasted for at least four months.

INT Toxicity over Natural Bacterial Assemblages from Surface Oligotrophic Waters: Implications for the Assessment of Respiratory Activity.

Plankton community respiration (R) is a major component of the carbon flux in aquatic ecosystems. However, current methods to measure actual respiration from oxygen consumption at relevant spatial scales are not sensitive enough in oligotrophic environments where respiration rates are very low. To overcome this drawback, more sensitive indirect enzymatic approaches are commonly used as R proxies. The in vivo electron transport system (ETSvivo) assay, which measures the reduction of (2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl tetrazolium chloride salt, INT) to INT-formazan in the presence of natural substrate levels, was recently proposed as an indirect reliable estimation of R for natural plankton communities. However, under in vivo conditions, formazan salts could be toxic to the cells. Here, we test the toxicity of 0.2 mM of final INT concentration, widely used for ETSvivo assays, on natural bacterial assemblages collected in coastal and oceanic waters off Gran Canaria (Canary Islands, subtropical North Atlantic), in eight independent experiments. After 0.5 h of incubation, a significant but variable decline in cell viability (14-49%) was observed in all samples inoculated with INT. Moreover, INT also inhibited leucine uptake in less than 90 min of incubation. In the light of these results, we argue that enzymatic respiratory rates obtained with the ETSvivo method need to be interpreted with caution to derive R in oceanic regions where bacteria largely contribute to community respiration. Moreover, the variable toxicity on bacterial assemblages observed in our experiments questions the use of a single R/ETSvivo relationship as a universal proxy for regional studies.

Microbial rhodopsins are major contributors to the solar energy captured in the sea.

All known phototrophic metabolisms on Earth rely on one of three categories of energy-converting pigments: chlorophyll-a (rarely -d), bacteriochlorophyll-a (rarely -b), and retinal, which is the chromophore in rhodopsins. While the significance of chlorophylls in solar energy capture has been studied for decades, the contribution of retinal-based phototrophy to this process remains largely unexplored. We report the first vertical distributions of the three energy-converting pigments measured along a contrasting nutrient gradient through the Mediterranean Sea and the Atlantic Ocean. The highest rhodopsin concentrations were observed above the deep chlorophyll-a maxima, and their geographical distribution tended to be inversely related to that of chlorophyll-a. We further show that proton-pumping proteorhodopsins potentially absorb as much light energy as chlorophyll-a-based phototrophy and that this energy is sufficient to sustain bacterial basal metabolism. This suggests that proteorhodopsins are a major energy-transducing mechanism to harvest solar energy in the surface ocean.

Organic carbon budget for the eastern boundary of the North Atlantic subtropical gyre: major role of DOC in mesopelagic respiration.

Transports of suspended particulate (POCsusp) and dissolved (DOC) organic carbon are inferred from a box-model covering the eastern boundary of the North Atlantic subtropical gyre. Corresponding net respiration rates (R) are obtained from a net organic carbon budget that is based on the transport estimates, and includes both vertical and lateral fluxes. The overall R in the mesopelagic layer (100-1500 m) is 1.6 ± 0.4 mmol C m-2 d-1. DOC accounts for up to 53% of R as a result of drawdown of organic carbon within Eastern North Atlantic Central Water (ENACW) that is entrained into sinking Mediterranean Overflow Water (MOW) that leads to formation of Mediterranean water (MW) at intermediate depths (~900 m). DOC represents 90% of the respired non-sinking organic carbon. When converted into oxygen units, the computed net respiration rate represents less than half the oxygen utilization rates (OUR) reported for the mesopelagic waters of the subtropical North Atlantic. Mesoscale processes in the area, not quantified with our approach, could account in part for the OUR differences observed between our carbon budget and other published studies from the North Atlantic, although seasonal or interannual variability could also be responsible for the difference in the estimates.

Deep-ocean dissolved organic matter reactivity along the Mediterranean Sea: does size matter?

Despite of the major role ascribed to marine dissolved organic matter (DOM) in the global carbon cycle, the reactivity of this pool in the dark ocean is still poorly understood. Present hypotheses, posed within the size-reactivity continuum (SRC) and the microbial carbon pump (MCP) conceptual frameworks, need further empirical support. Here, we provide field evidence of the soundness of the SRC model. We sampled the high salinity core-of-flow of the Levantine Intermediate Water along its westward route through the entire Mediterranean Sea. At selected sites, DOM was size-fractionated in apparent high (aHMW) and low (aLMW) molecular weight fractions using an efficient ultrafiltration cell. A percentage decline of the aHMW DOM from 68-76% to 40-55% was observed from the Levantine Sea to the Strait of Gibraltar in parallel with increasing apparent oxygen utilization (AOU). DOM mineralization accounted for 30 ± 3% of the AOU, being the aHMW fraction solely responsible for this consumption, verifying the SRC model in the field. We also demonstrate that, in parallel to this aHMW DOM consumption, fluorescent humic-like substances accumulate in both fractions and protein-like substances decline in the aLMW fraction, thus indicating that not only size matters and providing field support to the MCP model.

[A prospective study to assess the burden of influenza-related hospitalizations and emergency department visits among children in Bilbao, Spain (2010-2011)]. / Estudio prospectivo para estimar la carga de hospitalización y visitas a urgencias de la gripe en población pediátrica en Bilbao (2010-2011).

INTRODUCTION: This study was undertaken to estimate the burden of morbidity associated with laboratory-confirmed influenza in children below 15 years of age. PATIENTS AND METHODS: Children presenting with acute respiratory infection and/or isolated fever at the Basurto University Hospital, Bilbao, Spain between November 2010 and May 2011 were included in this study (NCT01592799). Two nasopharyngeal secretion samples were taken from each; one for a rapid influenza diagnostic test in the emergency department, and the second for laboratory analysis using real-time polymerase chain reaction and viral culture. RESULTS: A total of 501 children were recruited, of whom 91 were hospitalized. Influenza diagnosis was confirmed in 131 children (26.1%); 120 of 410 (29.3%) treated as outpatients and 11 of 91 (12.1%) hospitalized children. A total of 370 of 501 children (73.9%) had no laboratory test positive for influenza. The proportion of subjects with other respiratory viruses was 145/501 (28.9%) cases and co-infection with the influenza virus plus another respiratory virus was detected in 7/501 (1.4%) cases. Influenza virus types were: A (H1N1 and H3N2) 53.2% (67/126); B (Victoria and Yamagata) 46.0% (58/126); A+B 0.8% (1/126). The median direct medical costs associated with each case of laboratory-confirmed influenza was €177.00 (N=131). No significant differences were observed between the medical costs associated with influenza A and B. CONCLUSION: Almost half of the cases were influenza virus B type. The administration of a vaccine containing influenza A and B types to children below 15 years of age might reduce the overall burden of the illness.

A prospective study to assess the burden of influenza-related hospitalizations and emergency department visits among children in Bilbao, Spain (2010-2011).

INTRODUCTION: This study was undertaken to estimate the burden of morbidity associated with laboratory-confirmed influenza in children below 15 years of age. PATIENTS AND METHODS: Children presenting with acute respiratory infection and/or isolated fever at the Basurto University Hospital, Bilbao, Spain between November 2010 and May 2011 were included in this study (NCT01592799). Two nasopharyngeal secretion samples were taken from each; one for a rapid influenza diagnostic test in the emergency department, and the second for laboratory analysis using real-time polymerase chain reaction and viral culture. RESULTS: A total of 501 children were recruited, of whom 91 were hospitalized. Influenza diagnosis was confirmed in 131 children (26.1%); 120 of 410 (29.3%) treated as outpatients and 11 of 91 (12.1%) hospitalized children. A total of 370 of 501 children (73.9%) had no laboratory test positive for influenza. The proportion of subjects with other respiratory viruses was 145/501 (28.9%) cases and co-infection with the influenza virus plus another respiratory virus was detected in 7/501 (1.4%) cases. Influenza virus types were: A (H1N1 and H3N2) 53.2% (67/126); B (Victoria and Yamagata) 46.0% (58/126); A + B 0.8% (1/126). The median direct medical costs associated with each case of laboratory-confirmed influenza was €177.00 (N = 131). No significant differences were observed between the medical costs associated with influenza A and B. CONCLUSION: Almost half of the cases were influenza virus B type. The administration of a vaccine containing influenza A and B types to children below 15 years of age might reduce the overall burden of the illness.

INTRODUCCIÓN: El estudio se llevó a cabo para estimar la carga de enfermedad de la gripe confirmada por laboratorio en niños menores de 15 años. PACIENTES Y MÉTODOS: Los niños que acudieron al Hospital Universitario de Basurto con síntomas de infección respiratoria aguda y/o fiebre aislada entre noviembre de 2010 y mayo de 2011 fueron incluidos en el estudio (NCT01592799). Se tomaron 2 muestras de secreción nasofaríngea: una para un test de diagnóstico rápido en el Servicio de Urgencias y otra para análisis en laboratorio con reacción en cadena de la polimerasa en tiempo real y cultivo viral. RESULTADOS: Se seleccionó a un total de 501 niños, de los que 91 fueron hospitalizados. El diagnóstico de gripe se confirmó en 131 (26,1%); 120/410 (29,3%) fueron tratados ambulatoriamente y 11/91 (12,1%), hospitalizados. En 370/501 niños (73,9%) el resultado no fue positivo. La proporción de otros virus respiratorios fue 145/501 (28,9%) casos y de coinfección con otro virus respiratorio además de gripe de 7/501 (1,4%). Los tipos de virus de gripe fueron: A (H1N1 y H3N2) 53,2% (67/126); B (Victoria y Yamagata) 46,0% (58/126); A + B 0,8% (1/126). El coste médico directo medio asociado con cada caso de gripe confirmada fue de 177,00 € (N = 131). No se observaron diferencias estadísticamente significativas entre el coste asociado con gripe A o B. CONCLUSIÓN: Casi la mitad de los casos fueron virus de gripe B. La administración de una vacuna que incluya tipos A y B de gripe debería reducir la carga de la enfermedad.

Safety and persistence of the humoral and cellular immune responses induced by 2 doses of an AS03-adjuvanted A(H1N1)pdm09 pandemic influenza vaccine administered to infants, children and adolescents: Two open, uncontrolled studies.

In children, 2 AS03-adjuvanted A(H1N1)pdm09 vaccine doses given 21 days apart were previously shown to induce a high humoral immune response and to have an acceptable safety profile up to 42 days following the first vaccination. Here, we analyzed the persistence data from 2 open-label studies, which assessed the safety, and humoral and cell-mediated immune responses induced by 2 doses of this vaccine. The first study was a phase II, randomized trial conducted in 104 children aged 6-35 months vaccinated with the A(H1N1)pdm09 vaccine containing 1.9 µg haemagglutinin antigen (HA) and AS03B (5.93 mg tocopherol) and the second study, a phase III, non-randomized trial conducted in 210 children and adolescents aged 3-17 years vaccinated with the A(H1N1)pdm09 vaccine containing 3.75 µg HA and AS03A (11.86 mg tocopherol). Approximately one year after the first dose, all children with available data were seropositive for haemagglutinin inhibition and neutralising antibody titres, but a decline in geometric mean antibody titres was noted. The vaccine induced a cell-mediated immune response in terms of antigen-specific CD4(+) T-cells, which persisted up to one year post-vaccination. The vaccine did not raise any safety concern, though these trials were not designed to detect rare events. In conclusion, 2 doses of the AS03-adjuvanted A(H1N1)pdm09 vaccine at 2 different dosages had a clinically acceptable safety profile, and induced high and persistent humoral and cell-mediated immune responses in children aged 6-35 months and 3-17 years. These studies have been registered at www.clinicaltrials.gov NCT00971321 and NCT00964158.

[Acceptability of the HPV vaccine among Spanish university students in the pre-vaccine era: a cross-sectional study]. / Aceptabilidad de la vacuna contra el VPH en estudiantes universitarios españoles durante la etapa pre-vacunal: un estudio transversal.

INTRODUCTION: Cervical cancer (CC), the second most common cause of cancer deaths in women, is associated with the infection of human papillomavirus (HPV) and is more prevalent in women between the ages of 20 and 24. This research is aimed to determine the background about CC, the human papillomavirus infection and its vaccine, assessing its acceptability in university students. METHODS: Cross-sectional study over 1,750 students from the University of Alicante (2008) selected at random, proportional associated to gender and studies, by a validated ad-hoc questionnaire. Percentages were computed, confidence intervals, contingency tables according to sex, age and type of studies, calculating adjusted odd ratios (OR). RESULTS: A sample with 58.6 % of women and 6.6% of biohealth students was obtained. 87.3% were willing to have the vaccine to prevent human papillomavirus (HPV), 94.3% would give this vaccine to their daughters, and 48.0% had heard someone talk about the vaccine. 90.6% didn't have a lot of knowledge about the HPV infection and 82.2% didn't know much about the vaccine. 22.4% had knowledge of the association between HPV and CC. Women register higher OR in acknowledging the problem and are more receptive to having the vaccine. The HPV vaccine acceptability is associated to the sex, the confidence of vaccines as a preventive method; the influence of the background is low in relation to the vaccine predisposition. CONCLUSIONS: A high acceptability of the vaccine was observed in the period of the study. Raising confidence in people about the vaccines can influence for a better predisposition to be vaccinated.

Transient changes in bacterioplankton communities induced by the submarine volcanic eruption of El Hierro (Canary Islands).

The submarine volcanic eruption occurring near El Hierro (Canary Islands) in October 2011 provided a unique opportunity to determine the effects of such events on the microbial populations of the surrounding waters. The birth of a new underwater volcano produced a large plume of vent material detectable from space that led to abrupt changes in the physical-chemical properties of the water column. We combined flow cytometry and 454-pyrosequencing of 16S rRNA gene amplicons (V1-V3 regions for Bacteria and V3-V5 for Archaea) to monitor the area around the volcano through the eruptive and post-eruptive phases (November 2011 to April 2012). Flow cytometric analyses revealed higher abundance and relative activity (expressed as a percentage of high-nucleic acid content cells) of heterotrophic prokaryotes during the eruptive process as compared to post-eruptive stages. Changes observed in populations detectable by flow cytometry were more evident at depths closer to the volcano (~70-200 m), coinciding also with oxygen depletion. Alpha-diversity analyses revealed that species richness (Chao1 index) decreased during the eruptive phase; however, no dramatic changes in community composition were observed. The most abundant taxa during the eruptive phase were similar to those in the post-eruptive stages and to those typically prevalent in oceanic bacterioplankton communities (i.e. the alphaproteobacterial SAR11 group, the Flavobacteriia class of the Bacteroidetes and certain groups of Gammaproteobacteria). Yet, although at low abundance, we also detected the presence of taxa not typically found in bacterioplankton communities such as the Epsilonproteobacteria and members of the candidate division ZB3, particularly during the eruptive stage. These groups are often associated with deep-sea hydrothermal vents or sulfur-rich springs. Both cytometric and sequence analyses showed that once the eruption ceased, evidences of the volcano-induced changes were no longer observed.

The submarine volcano eruption off El Hierro Island: effects on the scattering migrant biota and the evolution of the pelagic communities.

The submarine volcano eruption off El Hierro Island (Canary Islands) on 10 October 2011 promoted dramatic perturbation of the water column leading to changes in the distribution of pelagic fauna. To study the response of the scattering biota, we combined acoustic data with hydrographic profiles and concurrent sea surface turbidity indexes from satellite imagery. We also monitored changes in the plankton and nekton communities through the eruptive and post-eruptive phases. Decrease of oxygen, acidification, rising temperature and deposition of chemicals in shallow waters resulted in a reduction of epipelagic stocks and a disruption of diel vertical migration (nocturnal ascent) of mesopelagic organisms. Furthermore, decreased light levels at depth caused by extinction in the volcanic plume resulted in a significant shallowing of the deep acoustic scattering layer. Once the eruption ceased, the distribution and abundances of the pelagic biota returned to baseline levels. There was no evidence of a volcano-induced bloom in the plankton community.

Economic and psychosocial impact of rotavirus infection in Spain: a literature review.

Severe rotavirus gastroenteritis is common in children under 5 years of age. A literature review was performed to investigate the economic and psychosocial impact of rotavirus infection in children in this age group. We retrieved 56 articles on the economic burden of the disease in Europe, 18 of them reported data from Spain; 8 articles were retrieved analysing its psychosocial impact. In Spain, rotavirus is responsible for 14% to 30% of all cases of gastroenteritis, and a quarter of these require hospitalisation. It is also associated with high use of health care resources (emergency and primary care visits). Rotavirus gastroenteritis costs the Spanish national health system EUR 28 million a year and causes productivity loss in two-thirds of parents (mean of 4 days). Taking into account these costs, it was estimated that implementing universal vaccination could prevent 76% to 95% of hospital admissions due to rotavirus gastroenteritis, as well as reduce emergency and paediatric visits, nosocomial infections, and days missed from work (77% reduction). Rotavirus gastroenteritis also has a considerable psychosocial impact on the family, although it is difficult to compare results due to the diversity of study designs and the low specificity of the measurement tools used. It also causes high stress among parents, adding to their workload and adversely affecting their quality of life.

Krill excretion boosts microbial activity in the Southern Ocean.

Antarctic krill are known to release large amounts of inorganic and organic nutrients to the water column. Here we test the role of krill excretion of dissolved products in stimulating heterotrophic bacteria on the basis of three experiments where ammonium and organic excretory products released by krill were added to bacterial assemblages, free of grazers. Our results demonstrate that the addition of krill excretion products (but not of ammonium alone), at levels expected in krill swarms, greatly stimulates bacteria resulting in an order-of-magnitude increase in growth and production. Furthermore, they suggest that bacterial growth rate in the Southern Ocean is suppressed well below their potential by resource limitation. Enhanced bacterial activity in the presence of krill, which are major sources of DOC in the Southern Ocean, would further increase recycling processes associated with krill activity, resulting in highly efficient krill-bacterial recycling that should be conducive to stimulating periods of high primary productivity in the Southern Ocean.

Carbon dynamics within cyclonic eddies: insights from a biomarker study.

It is generally assumed that episodic nutrient pulses by cyclonic eddies into surface waters support a significant fraction of the primary production in subtropical low-nutrient environments in the northern hemisphere. However, contradictory results related to the influence of eddies on particulate organic carbon (POC) export have been reported. As a step toward understanding the complex mechanisms that control export of material within eddies, we present here results from a sediment trap mooring deployed within the path of cyclonic eddies generated near the Canary Islands over a 1.5-year period. We find that, during summer and autumn (when surface stratification is stronger, eddies are more intense, and a relative enrichment in CaCO3 forming organisms occurs), POC export to the deep ocean was 2-4 times higher than observed for the rest of the year. On the contrary, during winter and spring (when mixing is strongest and the seasonal phytoplankton bloom occurs), no significant enhancement of POC export associated with eddies was observed. Our biomarker results suggest that a large fraction of the material exported from surface waters during the late-winter bloom is either recycled in the mesopelagic zone or bypassed by migrant zooplankton to the deep scattering layer, where it would disaggregate to smaller particles or be excreted as dissolved organic carbon. Cyclonic eddies, however, would enhance carbon export below 1000 m depth during the summer stratification period, when eddies are more intense and frequent, highlighting the important role of eddies and their different biological communities on the regional carbon cycle.

Bacterial versus archaeal origin of extracellular enzymatic activity in the Northeast Atlantic deep waters.

We determined the total and dissolved extracellular enzymatic activity (EEA) of α-glucosidase and ß-glucosidase (AGase and BGase), alkaline phosphatase (APase) and leucine aminopeptidase (LAPase) activities in the epi-, meso- and bathypelagic waters of the subtropical Northeast Atlantic. EEA was also determined in treatments in which bacterial EEA was inhibited by erythromycin. Additionally, EEA decay experiments were performed with surface and deep waters to determine EEA lifetimes in both water masses. The proportion of dissolved to total EEA (66-89 %, 44-88 %, 57-82 % and 86-100 % for AGase, BGase, APase and LAPase, respectively) was generally higher than the cell-associated (i.e., particulate) EEA. The percentage of dissolved to total EEA was inversely proportional to the percentage of erythromycin-inhibited to total EEA. Since erythromycin-inhibited plus dissolved EEA equaled total EEA, this tentatively suggests that cell-associated EEA in the open oceanic water column is almost exclusively of bacterial origin. The decay constants of dissolved EEA were in the range of 0.002-0.048 h(-1) depending on the type of extracellular enzyme, temperature and depth in the water column. Although dissolved EEA can have different origins, the major contribution of Bacteria to cell-associated EEA and the long life-time of dissolved EEA suggest that Bacteria-and not mesophilic Archaea-are essentially the main producers of EEA in the open subtropical Northeast Atlantic down to bathypelagic layers.