| 1. |
- Baltar, Federico, et al.
(författare)
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Bacterial Versus Archaeal Origin of Extracellular Enzymatic Activity in the Northeast Atlantic Deep Waters
- 2013
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Ingår i: Microbial Ecology. - Springer-Verlag : Springer Science and Business Media LLC. - 0095-3628 .- 1432-184X. ; 65:2, s. 277-288
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Tidskriftsartikel (refereegranskat)abstract
- We determined the total and dissolved extracellularenzymatic activity (EEA) of α-glucosidase and β-glucosidase(AGase and BGase), alkaline phosphatase (APase) and leucineaminopeptidase (LAPase) activities in the epi-, meso- andbathypelagic waters of the subtropical Northeast Atlantic.EEA was also determined in treatments in which bacterialEEAwas inhibited by erythromycin. Additionally, EEA decayexperiments were performed with surface and deep waters todetermine EEA lifetimes in both water masses. The proportionof dissolved to total EEA (66–89 %, 44–88 %, 57–82 % and86–100 % for AGase, BGase, APase and LAPase, respectively)was generally higher than the cell-associated (i.e.,particulate) EEA. The percentage of dissolved to total EEAwas inversely proportional to the percentage of erythromycininhibitedto total EEA. Since erythromycin-inhibited plusdissolved EEA equaled total EEA, this tentatively suggeststhat cell-associated EEA in the open oceanic water column isalmost exclusively of bacterial origin. The decay constants ofdissolved EEAwere in the range of 0.002–0.048 h−1 dependingon the type of extracellular enzyme, temperature and depthin the water column. Although dissolved EEA can have differentorigins, the major contribution of Bacteria to cellassociatedEEA and the long life-time of dissolved EEAsuggest that Bacteria—and not mesophilic Archaea—areessentially the main producers of EEA in the open subtropicalNortheast Atlantic down to bathypelagic layers.
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| 2. |
- Baltar, Federico, et al.
(författare)
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Cell-free extracellular enzymatic activity is linked to seasonal temperature changes : a case study in the Baltic Sea
- 2016
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 13:9, s. 2815-2821
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Tidskriftsartikel (refereegranskat)abstract
- Extracellular enzymatic activities (EEA) are a crucial step on the degradation of organic matter. Dissolved (cell-free) extracellular enzymes in seawater can make up a significant contribution of the bulk EEA. However, the factors controlling the proportion of dissolved EEA in the marine environment remain unknown. Here we studied the seasonal changes in the proportion of dissolved relative to total EEA (of alkaline phosphatase [APase], β-glucosidase, [BGase], and leucine aminopeptidase, [LAPase]), in the Baltic Sea for 18 months. The proportio n of dissolved EEA ranged between 37-100%, 0-100%, 34-100% for APase, BGase and LAPase, respectively. A consistent seasonal pattern in the proportion of dissolved EEA was found among all the studied enzymes, with values up to 100% during winter and <40% du ring summer. A significant negative relation was found between the 21proportion of dissolved EEA and temperature, indicating that temperature might be a critical factor controlling the proportion of dissolved relative to total EEA in marine environments. Our results suggest a strong decoupling of hydrolysis rates from mi crobial dynamics in cold waters. This implies that under cold conditions, cell-free enzymes can contribute to substrate availability at large distances from the producing cell, increasing the dissociation between the hydrolysis of organic compounds and the actual microbes producing the enzymes. This also indicates that global warming could come to affect the hydrolysis of organic matter by reducing the hydrolytic activity of cell-free enzymes.
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| 3. |
- Baltar, Federico, et al.
(författare)
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Evidence of prokaryotic metabolism on suspended particulate organic matter in the dark waters of the (sub)tropical North Atlantic
- 2009
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 54:1, s. 182-193
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of prokaryotic abundance (PA), respiratory activity (ETS), heterotrophic production (PHP), and suspended particulate (POM) and dissolved (DOM) organic matter was determined in the meso- and bathypelagic waters of the (sub) tropical North Atlantic. PA decreased by one order of magnitude from the lower euphotic zone to the bathypelagic waters, while ETS decreased by two and PHP by three orders of magnitude. On a section following the Mid-Atlantic Ridge from 35 degrees N to 5 degrees N, ETS below 1000-m depth increased southwards up to three-fold. This latitudinal gradient in the deep waters was paralleled by a six-fold increase in Particulate Organic Carbon (POC), whereas no trend was apparent in the DOM distribution. Significant correlations between POM and ETS were obtained in the water masses between 1000-m and 3000-m depth, the Antarctic Intermediate Water and the North East Atlantic Deep Water. A strong imbalance in the dark ocean was found between prokaryotic carbon demand (estimated through two different approaches) and the carbon sinking flux derived from sediment-trap records corrected with Th-230. The imbalance was greater when deeper in the water column, suggesting that the suspended carbon pool must account for most of the carbon deficit. Our results, together with other recent findings discussed in this paper, indicate that microbial life in the dark ocean is likely more dependent on slowly sinking or buoyant, laterally advected suspended particles than hitherto assumed.
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| 4. |
- Baltar, Federico, et al.
(författare)
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High dissolved extracellular enzymatic activity in the deep Central Atlantic Ocean
- 2010
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 58:3, s. 287-302
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Baltar, Federico, et al.
(författare)
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Major Effect of Hydrogen Peroxide on Bacterioplankton Metabolism in the Northeast Atlantic
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:4
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Tidskriftsartikel (refereegranskat)abstract
- Reactive oxygen species such as hydrogen peroxide have the potential to alter metabolic rates of marine prokaryotes, ultimately impacting the cycling and bioavailability of nutrients and carbon. We studied the influence of H2O2 on prokaryotic heterotrophic production (PHP) and extracellular enzymatic activities (i.e., beta-glucosidase [BGase], leucine aminopeptidase [LAPase] and alkaline phosphatase [APase]) in the subtropical Atlantic. With increasing concentrations of H2O2 in the range of 100-1000 nM, LAPase, APase and BGase were reduced by up to 11, 23 and 62%, respectively, in the different water layers. Incubation experiments with subsurface waters revealed a strong inhibition of all measured enzymatic activities upon H2O2 amendments in the range of 10-500 nM after 24 h. H2O2 additions also reduced prokaryotic heterotrophic production by 36-100% compared to the rapid increases in production rates occurring in the unamended controls. Our results indicate that oxidative stress caused by H2O2 affects prokaryotic growth and hydrolysis of specific components of the organic matter pool. Thus, we suggest that oxidative stress may have important consequences on marine carbon and energy fluxes.
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| 6. |
- Baltar, Federico, et al.
(författare)
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Marine bacterial community structure resilience to changes in protist predation under phytoplankton bloom conditions
- 2016
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 10:3, s. 568-581
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Tidskriftsartikel (refereegranskat)abstract
- To test whether protist grazing selectively affects the composition of aquatic bacterial communities, we combined high-throughput sequencing to determine bacterial community composition with analyses of grazing rates, protist and bacterial abundances and bacterial cell sizes and physiological states in a mesocosm experiment in which nutrients were added to stimulate a phytoplankton bloom. A large variability was observed in the abundances of bacteria (from 0.7 to 2.4 x 10(6) cells per ml), heterotrophic nanoflagellates (from 0.063 to 2.7 x 10(4) cells per ml) and ciliates (from 100 to 3000 cells per l) during the experiment (similar to 3-, 45- and 30-fold, respectively), as well as in bulk grazing rates (from 1 to 13 x 10(6) bacteria per ml per day) and bacterial production (from 3 to 379 mu g per Cl per day) (1 and 2 orders of magnitude, respectively). However, these strong changes in predation pressure did not induce comparable responses in bacterial community composition, indicating that bacterial community structure was resilient to changes in protist predation pressure. Overall, our results indicate that peaks in protist predation (at least those associated with phytoplankton blooms) do not necessarily trigger substantial changes in the composition of coastal marine bacterioplankton communities.
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| 7. |
- Baltar, Federico, 1982-, et al.
(författare)
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Mesoscale eddies: hot-spots for prokaryotic diversity and function in the ocean
- 2010
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 4, s. 975-988
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the effects of mesoscale eddies on prokaryotic assemblage structure and activity, we sampled two cyclonic eddies (CEs) and two anticyclonic eddies (AEs) in the permanent eddy-field downstream the Canary Islands. The eddy stations were compared with two far-field (FF) stations located also in the Canary Current, but outside the influence of the eddy field. The distribution of prokaryotic abundance (PA), bulk prokaryotic heterotrophic activity (PHA), various indicators of single-cell activity (such as nucleic acid content, proportion of live cells, and fraction of cells actively incorporating leucine), as well as bacterial and archaeal community structure were determined from the surface to 2000 m depth. In the upper epipelagic layer (0–200 m), the effect of eddies on the prokaryotic community was more apparent, as indicated by the higher PA, PHA, fraction of living cells, and percentage of active cells incorporating leucine within eddies than at FF stations. Prokaryotic community composition differed also between eddy and FF stations in the epipelagic layer. In the mesopelagic layer (200–1000 m), there were also significant differences in PA and PHA between eddy and FF stations, although in general, there were no clear differences in community composition or single-cell activity. The effects on prokaryotic activity and community structure were stronger in AE than CE, decreasing with depth in both types of eddies. Overall, both types of eddies show distinct community compositions (as compared with FF in the epipelagic), and represent oceanic ‘hotspots’ of prokaryotic activity (in the epi- and mesopelagic realms).
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| 8. |
- Baltar, Federico, et al.
(författare)
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Mesoscale variability modulates seasonal changes in the trophic structure of nano- and picoplankton communities across the NW Africa-Canary Islands transition zone
- 2009
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611 .- 1873-4472. ; 83:1-4, s. 180-188
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Tidskriftsartikel (refereegranskat)abstract
- The variability of picoplankton and nanoplankton autotrophic (A) and heterotrophic (H) communities was studied along a zonal gradient extending from the NW African shelf to 500 km offshore in two contrasting seasons of the year: early spring (spring) and summer (summer). Plankton abundance was significantly higher in summer than in spring. In particular, heterotrophic prokaryotes (HP) and Prochlorococcus (Proc) were an order of magnitude more abundant in summer, presumably due to a higher loading of dissolved organic matter and higher temperatures. The average ratio of A to H biomass was lower during the summer. Over the African shelf, picoplankton was lowest during summer, while both the autotrophic and heterotrophic nanoflagellates (ANF and HNF) showed the highest abundances. In contrast, in spring, the highest abundance of Picoeukaryotes (PE) and Synechococcus (Syn) was found over or close to the shelf. The offshore sampling sections intersected a complex area of strong mesoscale variability, which affected the plankton distribution. In summer, the entrainment of an upwelling filament around a cyclonic eddy provoked the increase of HP and Syn abundances by about one order of magnitude over the surrounding waters, while PE were more abundant over the core of the eddy (probably due to nutrient pumping). In spring, HP and Syn were more abundant at the boundaries of an anticyclonic eddy and in the filament (where PE also increased). Proc abundance increased up to one order of magnitude in the core of the eddy and in the eddy-oceanic waters front. ANF and HNF showed the highest abundances in the filament and the eddy. in summary, although seasonality affects the background variability in microplankton communities, the mesoscale variability found in the Canary Islands transition zone strongly modulates the patterns of distribution, abundances and changes in community structure, altering the A to H ratio and concomitantly playing a key role modifying the carbon pathways within the food web in the region.
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| 9. |
- Baltar, Federico, et al.
(författare)
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Microbial functioning and community structure variability in the mesopelagic and epipelagic waters of the subtropical Northeast Atlantic Ocean.
- 2012
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 78:9, s. 3309-3316
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Tidskriftsartikel (refereegranskat)abstract
- We analyzed the regional distribution of bulk heterotrophic prokaryotic activity (leucine incorporation) and selected single-cell parameters (cell viability and nucleic acid content) as parameters for microbial functioning, as well as bacterial and archaeal community structure in the epipelagic (0-200 m) and mesopelagic (200-1000 m) subtropical Northeast Atlantic Ocean. We selectively sampled three contrasting regions covering a wide range of surface productivity and oceanographic properties within the same basin: (i) the eddy field south of the Canary Islands, (ii) the open-ocean Subtropical Gyre and (iii) the upwelling filament off Cape Blanc. In the epipelagic waters, a high regional variation in hydrographic parameters and bacterial community structure was detected accompanied, however, by a low variability in microbial functioning. In contrast, mesopelagic microbial functioning was highly variable between the studied regions despite the homogeneous abiotic conditions found therein. More microbial functioning parameters indicated differences among the three regions within the mesopelagic (i.e., viability of cells, nucleic acid content, cell-specific heterotrophic activity, nanoflagellate abundance, prokaryotic to nanoflagellate abundance ratio) than in the epipelagic (i.e., bulk activity, nucleic acid content and nanoflagellate abundance) waters. Our results show that the mesopelagic realm in the NE Atlantic is, in terms of microbial activity, more heterogeneous than its epipelagic counterpart, probably linked to mesoscale hydrographical variations.
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| 10. |
- Baltar, Federico, et al.
(författare)
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Prokaryotic carbon utilization in the dark ocean: : growth efficiency, leucine-to-carbon conversion factors, and their relation
- 2010
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 60:3, s. 227-232
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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