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  • 1.
    Algesten, Grete
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Sobek, Sebastian
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Tranvik, Lars J
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Contribution of sediment respiration to summer CO2 emission from boreal and subarctic lakes2005Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 50, nr 4, s. 529-535Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We measured sediment production of carbon dioxide (CO(2)) and methane (CH(4)) and the net flux of CO(2) across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were made in situ under ambient light conditions. The flux of CO(2) between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m(-2) day(-1) from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated to dissolved organic carbon (DOC) concentration in the water (r(2) = 0.61). The net flux of CO(2) across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed layer (r(2) = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration. Lakes with DOC concentrations <5.6 mg L(-1) had net consumption of CO(2) in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic (<2.6 mg L(-1)) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources.

  • 2. ANDERSSON, A
    et al.
    FALK, S
    Samuelsson, Göran
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysiologisk botanik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    HAGSTROM, A
    NUTRITIONAL CHARACTERISTICS OF A MIXOTROPHIC NANOFLAGELLATE, OCHROMONAS SP1989Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 17, nr 3, s. 251-262Artikkel i tidsskrift (Fagfellevurdert)
  • 3.
    Berggren, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Hydrological control of organic carbon support for bacterial growth in boreal headwater streams2009Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 57, nr 1, s. 170-178Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Terrestrial organic carbon is exported to freshwater systems where it serves as substrate for bacterial growth. Temporal variations in the terrigenous organic carbon support for aquatic bacteria are not well understood. In this paper, we demonstrate how the combined influence of landscape characteristics and hydrology can shape such variations. Using a 13-day bioassay approach, the production and respiration of bacteria were measured in water samples from six small Swedish streams (64° N, 19° E), draining coniferous forests, peat mires, and mixed catchments with typical boreal proportions between forest and mire coverage. Forest drainage supported higher bacterial production and higher bacterial growth efficiency than drainage from mires. The areal export of organic carbon was several times higher from mire than from forest at low runoff, while there was no difference at high flow. As a consequence, mixed streams (catchments including both mire and forest) were dominated by mire organic carbon with low support of bacterial production at low discharge situations but dominated by forest carbon supporting higher bacterial production at high flow. The stimulation of bacterial growth during high-flow episodes was a result of higher relative export of organic carbon via forest drainage rather than increased drainage of specific “high-quality” carbon pools in mire or forest soils.

  • 4.
    Berggren, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, SLU, Umeå.
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nutrient constraints on metabolism affect the temperature regulation of aquatic bacterial growth efficiency2010Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 60, nr 4, s. 894-902Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Inorganic nutrient availability and temperature are recognized as major regulators of organic carbon processing by aquatic bacteria, but little is known about how these two factors interact to control bacterial metabolic processes. We manipulated the temperature of boreal humic stream water samples within 0–25°C and measured bacterial production (BP) and respiration (BR) with and without inorganic nitrogen + phosphorus addition. Both BP and BR increased exponentially with temperature in all experiments, with Q 10 values varying between 1.2 and 2.4. The bacterial growth efficiency (BGE) showed strong negative relationships with temperature in nutrient-enriched samples and in natural stream water where community-level BP and BR were not limited by nutrients. However, there were no relationships between BGE and temperature in samples where BP and BR were significantly constrained by the inorganic nutrient availability. The results suggest that metabolic responses of aquatic bacterial communities to temperature variations can be strongly dependent on whether the bacterial metabolism is limited by inorganic nutrients or not. Such responses can have consequences for both the carbon flux through aquatic food webs and for the flux of CO2 from aquatic systems to the atmosphere.

  • 5.
    Bergström, Ann-Kristin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bacterioplankton production in humic Lake Örträsket in relation to input of bacterial cells and input of allochthonous organic carbon2000Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 39, nr 2, s. 101-115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to compare riverine bacteria input with lake water bacterial production and grazing loss with output loss, a bacterial cell budget was constructed for humic Lake Ortrasket in northern Sweden. The riverine input of bacterial cells in 1997 represented 29% of the number of bacterial cells produced within the layer of the lake affected by inlet water. A large share of the in situ lake bacterial production was consumed by grazers, mainly flagellates, which stresses the importance of bacteria as energy mobilizers for the pelagic food web in the lake. The bacterial production in Lake Ortrasket, which is almost entirely dependent on humic material as an energy source, was clearly stimulated by high flow episodes which brought high amounts of little degraded material into the lake. During base flow condition the bacterial production in the inlet rivers was high, which led to an input of more degraded material to the lake. This material did not stimulate the lake bacterial production. Internal factors that determined the utilization of the allochthonous DOC in the lake were the retention time and the exposure to light and high temperatures. Thus, the potential for in situ production of bacteria in Lake Ortrasket was to a large extent a function of how precipitation and runoff conditions affected terrestrial losses and river transport of humic material.

  • 6. Blomqvist, Peter
    et al.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Drakare, Stina
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Brydsten, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Effects of additions of DOC on pelagic biota in a clearwater system: results from a whole lake experiment in northern Sweden2001Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 42, nr 3, s. 383-394Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An oligotrophic clearwater lake, initially characterized by a pronounced dominance of autotrophic phytoplankton and mostly by one species, the green alga Botryococcus, was subject to additions of dissolved organic carbon in the form of white sugar (sucrose) during two consecutive years. The hypothesis tested was that it is organic carbon per se, and not other possible effects of humic substances, that determines the differences in structure of the planktonic ecosystem between humic and clearwater lakes. The additions of DOC resulted in a significant increase in bacterial biomass and a decrease in the biomass of autotrophic phytoplankton. The biomass of mixotrophic and heterotrophic flagellates instead increased significantly, whereas no effects were found to propagate to higher trophic levels. As a result of the changes among biota, total planktonic biomass also decreased to a level typical of nearby humic lakes. We suggest that it is the carbon component of humic material and its utilization by bacterioplankton that determines the structure and function of the pelagic food web in humic lakes.

  • 7.
    Dar, Shabir A
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet).
    Bijmans, Martijn F M
    Dinkla, Inez J T
    Geurkink, Bert
    Lens, Piet N L
    Dopson, Mark
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet).
    Population dynamics of a single-stage sulfidogenic bioreactor treating synthetic zinc-containing waste streams2009Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 58, nr 3, s. 529-537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Waste streams from industrial processes such as metal smelting or mining contain high concentrations of sulfate and metals with low pH. Dissimilatory sulfate reduction carried out by sulfate-reducing bacteria (SRB) at low pH can combine sulfate reduction with metal-sulfide precipitation and thus open possibilities for selective metal recovery. This study investigates the microbial diversity and population changes of a single-stage sulfidogenic gas-lift bioreactor treating synthetic zinc-rich waste water at pH 5.5 by denaturing gradient gel electrophoresis of 16S rRNA gene fragments and quantitative polymerase chain reaction. The results indicate the presence of a diverse range of phylogenetic groups with the predominant microbial populations belonging to the Desulfovibrionaceae from delta-Proteobacteria. Desulfovibrio desulfuricans-like populations were the most abundant among the SRB during the three stable phases of varying sulfide and zinc concentrations and increased from 13% to 54% of the total bacterial populations over time. The second largest group was Desulfovibrio marrakechensis-like SRB that increased from 1% to about 10% with decreasing sulfide concentrations. Desulfovibrio aminophilus-like populations were the only SRB to decrease in numbers with decreasing sulfide concentrations. However, their population was <1% of the total bacterial population in the reactor at all analyzed time points. The number of dissimilatory sulfate reductase (DsrA) gene copies per number of SRB cells decreased from 3.5 to 2 DsrA copies when the sulfide concentration was reduced, suggesting that the cells' sulfate-reducing capacity was also lowered. This study has identified the species present in a single-stage sulfidogenic bioreactor treating zinc-rich wastewater at low pH and provides insights into the microbial ecology of this biotechnological process.

  • 8.
    Figueroa, Daniela
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Rowe, Owen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Food and Environmental Sciences, Division of Microbiology and Biotechnology, University of Helsinki, Helsinki, Finland.
    Paczkowska, Joanna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Legrand, Catherine
    Andersson, Agneta
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Allochthonous Carbon - a major driver of bacterioplankton production in the subarctic Northern Baltic Sea2016Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 71, nr 4, s. 789-801Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Heterotrophic bacteria are, in many aquatic systems, reliant on autochthonous organic carbon as their energy source. One exception is low-productive humic lakes, where allochthonous dissolved organic matter (ADOM) is the major driver. We hypothesized that bacterial production (BP) is similarly regulated in subarctic estuaries that receive large amounts of riverine material. BP and potential explanatory factors were measured during May–August 2011 in the subarctic Råne Estuary, northern Sweden. The highest BP was observed in spring, concomitant with the spring river-flush and the lowest rates occurred during summer when primary production (PP) peaked. PLS correlations showed that ∼60 % of the BP variation was explained by different ADOM components, measured as humic substances, dissolved organic carbon (DOC) and coloured dissolved organic matter (CDOM). On average, BP was threefold higher than PP. The bioavailability of allochthonous dissolved organic carbon (ADOC) exhibited large spatial and temporal variation; however, the average value was low, ∼2 %. Bioassay analysis showed that BP in the near-shore area was potentially carbon limited early in the season, while BP at seaward stations was more commonly limited by nitrogen-phosphorus. Nevertheless, the bioassay indicated that ADOC could contribute significantly to the in situ BP, ∼60 %. We conclude that ADOM is a regulator of BP in the studied estuary. Thus, projected climate-induced increases in river discharge suggest that BP will increase in subarctic coastal areas during the coming century.

  • 9. Holmfeldt, Karin
    et al.
    Titelman, Josefin
    Riemann, Lasse
    Virus Production and Lysate Recycling in Different Sub-basins of the Northern Baltic Sea2010Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 60, nr 3, s. 572-580Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the Gulf of Bothnia, northern Baltic Sea, a large freshwater inflow creates north-southerly gradients in physico-chemical and biological factors across the two sub-basins, the Bothnian Bay (BB) and the Bothnian Sea. In particular, the sub-basins differ in nutrient limitation (nitrogen vs. phosphorus; P). Since viruses are rich in P, and virus production is commonly connected with bacterial abundance and growth, we hypothesized that the role of viral lysis differs between the sub-basins. Thus, we examined virus production and the potential importance of lysate recycling in surface waters along a transect in the Gulf of Bothnia. Surprisingly, virus production and total P were negatively correlated. In the BB, virus production rates were double those elsewhere in the system, although bacterial abundance and production were the lowest. In the BB, virus-mediated cell lysates could account for 70-180% and 100-250% of the bacterial carbon and P demand, respectively, while only 4-15% and 8-21% at the other stations. Low concentrations of dissolved DNA (D-DNA) with a high proportion of encapsulated DNA (viruses) in the BB suggested rapid turnover and high uptake of free DNA. The correlation of D-DNA and total P indicates that D-DNA is a particularly important nutrient source in the P-limited BB. Our study demonstrates large and counterintuitive differences in virus-mediated recycling of carbon and nutrients in two basins of the Gulf of Bothnia, which differ in microbial community composition and nutrient limitation.

  • 10.
    Jansson, Mats
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lymer, David
    Vrede, Katarina
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bacterioplankton growth and nutrient use efficiencies under variable organic carbon and inorganic phosphorus ratios2006Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 52, nr 2, s. 258-264Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We carried out enclosure experiments in an unproductive lake in northern Sweden and studied the effects of enrichment with different dissolved organic carbon (glucose)/inorganic phosphorous (DOC/Pi) ratios on bacterioplankton production (BP), growth efficiency (BGE), nutrient use efficiency (BNUE), growth rate, and specific respiration. We found considerable variation in BP, BGE, and BNUE along the tested DOC/Pi gradient. BGE varied between 0.87 and 0.24, with the highest values at low DOC/Pi ratios. BNUE varied between 40 and 9 g C g P−1, with high values at high DOC/Pi ratios. More DOC was thus allocated to growth when bacteria tended to be C-limited, and to respiration when bacteria were P-limited. Specific respiration was positively correlated with bacterial growth rate throughout the gradient. It is therefore possible that respiration was used to support growth in P-limited bacteria. The results indicated that BP can be limited by Pi when BNUE is at its maximum, by organic C when BGE is at its maximum, and by dual organic C and Pi limitation when BNUE and BGE have suboptimal values.

  • 11.
    Karlsson, Jan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bacterioplankton production in lakes along an altitude gradient in the subarctic north of Sweden2001Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 42, nr 3, s. 372-382Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examined changes in bacterioplankton standing stock and production in subarctic lakes in the north of Sweden to elucidate their coupling to lake physical, chemical, and biological characteristics. Sixteen lakes situated along an altitude gradient extending from the coniferous forest to the high-alpine belt were studied during 1998 and 1999. The summer mean bacterial numbers and production varied substantially between the lakes, with a general trend toward decreasing values with increasing altitude. The results demonstrate that P probably restricted bacterial utilization of DOC in the coniferous forest lakes, while low DOC concentrations limited bacterial growth during the summer in the alpine lakes. The primary production of plankton was insufficient to support bacterial production in the lakes. High input of allochthonous DOC to the alpine lakes in spring was sufficient both to increase the bacterial production and to induce P-limitation. As a consequence, there was a tendency toward higher bacterial activity in the spring compared to the summer in the alpine lakes. The results indicate that most of the bacterial standing stock and production are supported by allochthonous DOC plus DOC from benthic production, and more or less limited by the phosphorus supply. We therefore suggest that bacteria populations in subarctic lakes may be indirectly affected by climate variations through its impact on the input of DOC and nutrients from the lake catchments.

  • 12. Riemann, Lasse
    et al.
    Holmfeldt, Karin
    Titelman, Josefin
    Importance of Viral Lysis and Dissolved DNA for Bacterioplankton Activity in a P-Limited Estuary, Northern Baltic Sea2009Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 57, nr 2, s. 286-294Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Through lysis of bacterioplankton cells, viruses mediate an important, but poorly understood, pathway of carbon and nutrients from the particulate to the dissolved form. Via this activity, nutrient-rich cell lysates may become available to noninfected cells and support significant growth. However, the nutritional value of lysates for noninfected bacteria presumably depends on the prevailing nutrient limitation. In the present study, we examined dynamics of dissolved DNA (D-DNA) and viruses along a transect in the phosphorus (P)-limited A-re Estuary, northern Baltic Sea. We found that viruses were an important mortality factor for bacterioplankton and that their activity mediated a significant recycling of carbon and especially of P. Uptake of dissolved DNA accounted for up to 70% of the bacterioplankton P demand, and about a quarter of the D-DNA pool was supplied through viral lysis of bacterial cells. Generally, the importance of viral lysates and uptake of D-DNA was highest at the estuarine and offshore stations and was positively correlated with P limitation measured as alkaline phosphatase activity. Our results highlight the importance of viral activity for the internal recycling of principal nutrients and pinpoints D-DNA as a particularly relevant compound in microbial P dynamics.

  • 13. Rousk, Kathrin
    et al.
    Sorensen, Pernille L.
    Lett, Signe
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Michelsen, Anders
    Across-Habitat Comparison of Diazotroph Activity in the Subarctic2015Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 69, nr 4, s. 778-787Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nitrogen (N) fixation by N-2-fixing bacteria (diazotrophs) is the primary N input to pristine ecosystems like boreal forests and subarctic and arctic tundra. However, the contribution by the various diazotrophs to habitat N-2 fixation remains unclear. We present results from in situ assessments of N-2 fixation of five diazotroph associations (with a legume, lichen, feather moss, Sphagnum moss and free-living) incorporating the ground cover of the associations in five typical habitats in the subarctic (wet and dry heath, polygon-heath, birch forest, mire). Further, we assessed the importance of soil and air temperature, as well as moisture conditions for N-2 fixation. Across the growing season, the legume had the highest total as well as the highest fraction of N-2 fixation rates at habitat level in the heaths (> 85 % of habitat N-2 fixation), whereas the free-living diazotrophs had the highest N-2 fixation rates in the polygon heath (56 %), the lichen in the birch forest (87 %) and Sphagnum in the mire (100 %). The feather moss did not contribute more than 15 % to habitat N-2 fixation in any of the habitats despite its high ground cover. Moisture content seemed to be a major driver of N-2 fixation in the lichen, feather moss and free-living diazotrophs. Our results show that the range of N-2 fixers found in pristine habitats contribute differently to habitat N-2 fixation and that ground cover of the associates does not necessarily mirror contribution.

  • 14. Sjoqvist, C.
    et al.
    Kremp, A.
    Lindehoff, Elin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF). Department of Biology and Environmental Science, Centre for Ecology and Evolution in Microbial model Systems (EEMiS), Linnaeus University, Kalmar, Sweden.
    Båmstedt, Ulf
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Egardt, J.
    Gross, S.
    Jönsson, M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Larsson, Henrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Pohnert, G.
    Richter, H.
    Selander, E.
    Godhe, A.
    Effects of Grazer Presence on Genetic Structure of a Phenotypically Diverse Diatom Population2014Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 67, nr 1, s. 83-95Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Studies of predator-prey systems in both aquatic and terrestrial environments have shown that grazers structure the intraspecific diversity of prey species, given that the prey populations are phenotypically variable. Populations of phytoplankton have traditionally considered comprising only low intraspecific variation, hence selective grazing as a potentially structuring factor of both genetic and phenotypic diversity has not been comprehensively studied. In this study, we compared strain specific growth rates, production of polyunsaturated aldehydes, and chain length of the marine diatom Skeletonema marinoi in both grazer and non-grazer conditions by conducting monoclonal experiments. Additionally, a mesocosm experiment was performed with multiclonal experimental S. marinoi populations exposed to grazers at different levels of copepod concentration to test effects of grazer presence on diatom diversity in close to natural conditions. Our results show that distinct genotypes of a geographically restricted population exhibit variable phenotypic traits relevant to grazing interactions such as chain length and growth rates. Grazer presence affected clonal richness and evenness of multiclonal Skeletonema populations in the mesocosms, likely in conjunction with intrinsic interactions among the diatom strains. Only the production of polyunsaturated aldehydes was not affected by grazer presence. Our findings suggest that grazing can be an important factor structuring diatom population diversity in the sea and emphasize the importance of considering clonal differences when characterizing species and their role in nature.

  • 15. Soares, Ana R. A.
    et al.
    Kritzberg, Emma S.
    Custelcean, Ioana
    Berggren, Martin
    Bacterioplankton Responses to Increased Organic Carbon and Nutrient Loading in a Boreal Estuary-Separate and Interactive Effects on Growth and Respiration2018Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 76, nr 1, s. 144-155Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Increases in the terrestrial export of dissolved organic carbon (C) to rivers may be associated with additional loading of organic nitrogen (N) and phosphorus (P) to the coastal zone. However, little is known about how these resources interact in the regulation of heterotrophic bacterioplankton metabolism in boreal coastal ecosystems. Here, we measured changes in bacterioplankton production (BP) and respiration (BR) in response to full-factorial (C, N, and P) enrichment experiments at two sites within the A-re estuary, northern Sweden. The BR was stimulated by single C additions and further enhanced by combined additions of C and other nutrients. Single addition of N or P had no effect on BR rates. In contrast, BP was primarily limited by P at the site close to the river mouth and did not respond to C or N additions. However, at the site further away from the near the river mouth, BP was slightly stimulated by single additions of C. Possibly, the natural inflow of riverine bioavailable dissolved organic carbon induced local P limitation of BP near the river mouth, which was then exhausted and resulted in C-limited BP further away from the river mouth. We observed positive interactions between all elements on all responses except for BP at the site close to the river mouth, where P showed an independent effect. In light of predicted increases in terrestrial P and C deliveries, we expect future increases in BP and increases of BR of terrestrially delivered C substrates at the A-re estuary and similar areas.

  • 16.
    Säwström, Christin
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Anesio, M Alexandre
    Granéli, Wilhelm
    Laybourn-Parry, Johanna
    Seasonal viral loop dynamics in two large ultraoligotrophic Antarctic freshwater lakes.2007Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 53, nr 1, s. 1-11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of viruses on the microbial loop, with particular emphasis on bacteria, was investigated over an annual cycle in 2003-2004 in Lake Druzhby and Crooked Lake, two large ultraoligotrophic freshwater lakes in the Vestfold Hills, Eastern Antarctica. Viral abundance ranged from 0.16 to 1.56 x 10(9) particles L-1 and bacterial abundances ranged from 0.10 to 0.24 x 10(9) cells L-1, with the lowest bacterial abundances noted in the winter months. Virus-to-bacteria ratios (VBR) were consistently low in both lakes throughout the season, ranging from 1.2 to 8.4. lysogenic bacteria, determined by induction with mitomycin C, were detected on three sampling occasions out of 10 in both lakes. In Lake Druzhby and Crooked Lake, lysogenic bacteria made up between 18% and 73% of the total bacteria population during the lysogenic events. Bacterial production ranged from 8.2 to 304.9 x 10(6) cells L-1 day-1 and lytic viral production ranged from 47.5 to 718.4 x 10(6) viruslike particles L-1 day-1. When only considering primary production, heterotrophic nanoflagellate (HNF) grazing and viral lysis as the major contributors to the DOC pool (i.e., autochthonous sources), we estimated a high contribution from viruses during the winter months when >60% of the carbon supplied to the DOC pool originated from viral lysis. In contrast, during the summer <20% originated from viral lysis. Our study shows that viral process in ultraoligotrophic Antarctic lakes may be of quantitative significance with respect to carbon flow especially during the dark winter period.

  • 17. Thelaus, J
    et al.
    Andersson, A
    Broman, T
    Bäckman, S
    Granberg, M
    Karlsson, L
    Kuoppa, K
    Larsson, E
    Lundmark, E
    Lundström, JO
    Mathisen, Peter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Näslund, J
    Schafer, M
    Wahab, T
    Forsman, M
    Francisella tularensis subspecies holarctica occurs in swedish mosquitoes, persists through the developmental stages of laboratory-infected mosquitoes and is transmissible during blood feeding2014Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 67, nr 1, s. 96-107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In Sweden, mosquitoes are considered the major vectors of the bacterium Francisella tularensis subsp. holarctica, which causes tularaemia. The aim of this study was to investigate whether mosquitoes acquire the bacterium as aquatic larvae and transmit the disease as adults. Mosquitoes sampled in a Swedish area where tularaemia is endemic (A-rebro) were positive for the presence of F. tularensis deoxyribonucleic acid throughout the summer. Presence of the clinically relevant F. tularensis subsp. holarctica was confirmed in 11 out of the 14 mosquito species sampled. Experiments performed using laboratory-reared Aedes aegypti confirmed that F. tularensis subsp. holarctica was transstadially maintained from orally infected larvae to adult mosquitoes and that 25 % of the adults exposed as larvae were positive for the presence of F. tularensis-specific sequences for at least 2 weeks. In addition, we found that F. tularensis subsp. holarctica was transmitted to 58 % of the adult mosquitoes feeding on diseased mice. In a small-scale in vivo transmission experiment with F. tularensis subsp. holarctica-positive adult mosquitoes and susceptible mice, none of the animals developed tularaemia. However, we confirmed that there was transmission of the bacterium to blood vials by mosquitoes that had been exposed to the bacterium in the larval stage. Taken together, these results provide evidence that mosquitoes play a role in disease transmission in part of Sweden where tularaemia recurs.

  • 18.
    Vikström, Kevin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wikner, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Importance of Bacterial Maintenance Respiration in a Subarctic Estuary: a Proof of Concept from the Field2018Inngår i: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184XArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bacterial respiration contributes to atmospheric carbon dioxide accumulation and development of hypoxia and is a critical, often overlooked, component of ecosystem function. This study investigates the concept that maintenance respiration is a significant proportion of bacterial respiration at natural nutrient levels in the field, advancing our understanding of bacterial living conditions and energy strategies. Two river-sea transects of respiration and specific growth rates were analyzed representing low- and highproductivity conditions (by in situ bacterial biomass production) in a subarctic estuary, using an established ecophysiological linear model (the Pirt model) estimating maintenance respiration. The Pirt model was applicable to field conditions during high, but not low, bacterial biomass production. However, a quadratic model provided a better fit to observed data, accounting for the maintained respiration at low μ. A first estimate of maintenance respiration was 0.58 fmol O2 day−1 cell−1 by the quadratic model. Twenty percent to nearly all of the bacterial respiration was due to maintenance respiration over the observed range of μ (0.21– 0.002 day−1 ). In the less productive condition, bacterial specific respiration was high and without dependence on μ, suggesting enhanced bacterial energy expenditure during starvation. Annual maintenance respiration accounted for 58% of the total bacterioplankton respiration based on μ from monitoring data. Phosphorus availability occasionally, but inconsistently, explained some of the remaining variation in bacterial specific respiration. Bacterial maintenance respiration can constitute a large share of pelagic respiration and merit further study to understand bacterial energetics and oxygen dynamics in the aquatic environment.

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