Posts Tagged 'bacteria'

Response of Nodularia spumigena to pCO2 – Part 2: Exudation and extracellular enzyme activities

The filamentous and diazotrophic cyanobacterium Nodularia spumigena plays a major role in the productivity of the Baltic Sea as it forms extensive blooms regularly. Under phosphorus limiting conditions Nodularia spumigena has a high enzyme affinity for dissolved organic phosphorus (DOP) by production and release of alkaline phosphatase. Additionally, it is able to degrade proteinaceous compounds by expressing the extracellular enzyme leucine aminopeptidase. As atmospheric CO2 concentrations are increasing, we expect marine phytoplankton to experience changes in several environmental parameters including pH, temperature, and nutrient availability. The aim of this study was to investigate the combined effect of CO2-induced changes in seawater carbonate chemistry and of phosphate deficiency on the exudation of organic matter, and its subsequent recycling by extracellular enzymes in a Nodularia spumigena culture. Batch cultures of Nodularia spumigena were grown for 15 days aerated with three different pCO2 levels corresponding to values from glacial periods to future values projected for the year 2100. Extracellular enzyme activities as well as changes in organic and inorganic compound concentrations were monitored. CO2 treatment–related effects were identified for cyanobacterial growth, which in turn was influencing exudation and recycling of organic matter by extracellular enzymes. Biomass production was increased by 56.5% and 90.7% in the medium and high pCO2 treatment, respectively, compared to the low pCO2 treatment and simultaneously increasing exudation. During the growth phase significantly more mucinous substances accumulated in the high pCO2 treatment reaching 363 μg Gum Xanthan eq l−1 compared to 269 μg Gum Xanthan eq l−1 in the low pCO2 treatment. However, cell-specific rates did not change. After phosphate depletion, the acquisition of P from DOP by alkaline phosphatase was significantly enhanced. Alkaline phosphatase activities were increased by factor 1.64 and 2.25, respectively, in the medium and high compared to the low pCO2 treatment. In conclusion, our results suggest that Nodularia spumigena can grow faster under elevated pCO2 by enhancing the recycling of organic matter to acquire nutrients.

Continue reading ‘Response of Nodularia spumigena to pCO2 – Part 2: Exudation and extracellular enzyme activities’

Community-level response of coastal microbial biofilms to ocean acidification in a natural carbon dioxide vent ecosystem

The impacts of ocean acidification on coastal biofilms are poorly understood. Carbon dioxide vent areas provide an opportunity to make predictions about the impacts of ocean acidification. We compared biofilms that colonised glass slides in areas exposed to ambient and elevated levels of pCO2 along a coastal pH gradient, with biofilms grown at ambient and reduced light levels. Biofilm production was highest under ambient light levels, but under both light regimes biofilm production was enhanced in seawater with high pCO2. Uronic acids are a component of biofilms and increased significantly with high pCO2. Bacteria and Eukarya denaturing gradient gel electrophoresis profile analysis showed clear differences in the structures of ambient and reduced light biofilm communities, and biofilms grown at high pCO2 compared with ambient conditions. This study characterises biofilm response to natural seabed CO2 seeps and provides a baseline understanding of how coastal ecosystems may respond to increased pCO2 levels.

Continue reading ‘Community-level response of coastal microbial biofilms to ocean acidification in a natural carbon dioxide vent ecosystem’

Response of Nodularia spumigena to pCO2 – Part I: Growth, production and nitrogen cycling

Heterocystous cyanobacteria of the genus Nodularia form extensive blooms in the Baltic Sea contributing substantially to the total annual primary production. Moreover, they dispense a large fraction of new nitrogen to the ecosystem, when inorganic nitrogen concentration in summer is low. Thus, it is of great ecological importance to know how Nodularia will react to future environmental changes, in particular to increasing carbon dioxide (CO2) concentrations and what consequences there might arise for cycling of organic matter in the ocean. Here, we determined carbon (C) and dinitrogen (N2) fixation rates, growth, elemental stoichiometry of particulate organic matter and nitrogen turnover during batch growth of the heterocystous cyanobacterium Nodularia spumigena under glacial (180 ppm), present (380 ppm), and future (780 ppm) CO2 concentrations. Our results demonstrate an overall stimulating effect of rising pCO2 on C and N2 fixation, as well as on cell growth. An increase in pCO2 resulted in an elevation in growth rate, C and N2 fixation by 23%, 36% and 25%, respectively (180 ppm vs. 380 ppm) and by 27%, 2% and 4%, respectively (380 ppm vs. 780 ppm). Additionally, elevation in the carbon and nitrogen to phosphorus quota of the particulate biomass formed (POC:POP and PON:POP) was observed at high pCO2. Our findings suggest that rising pCO2 stimulates the growth of heterocystous diazotrophic cyanobacteria, in a similar way as reported for non-heterocystous diazotrophs. Implications for biogeochemical cycling and food web dynamics, as well as ecological and socio-economical aspects in the Baltic Sea are discussed.

Continue reading ‘Response of Nodularia spumigena to pCO2 – Part I: Growth, production and nitrogen cycling’

Virioplankton and bacterioplankton in a shallow CO2-dominated hydrothermal vent (Panarea Island, Tyrrhenian Sea)

Gas hydrothermal vents are used as a natural analogue for studying the effects of CO2 leakage from hypothetical shallow marine storage sites on benthic and pelagic systems. This study investigated the interrelationships between planktonic prokaryotes and viruses in the Panarea Islands hydrothermal system (southern Tyrrhenian Sea, Italy), especially their abundance, distribution and diversity. No difference in prokaryotic abundance was shown between high-CO2 and control sites. The community structure displayed differences between fumarolic field and the control, and between surface and bottom waters, the latter likely due to the presence of different water masses. Bacterial assemblages were qualitatively dominated by chemo- and photoautotrophic organisms, able to utilise both CO2 and H2S for their metabolic requirements. From significantly lower virioplankton abundance in the proximity of the exhalative area together with particularly low Virus-to-Prokaryotes Ratio, we inferred a reduced impact on prokaryotic abundance and proliferation. Even if the fate of viruses in this particular condition remains still unknown, we consider that lower viral abundance could reflect in enhancing the energy flow to higher trophic levels, thus largely influencing the overall functioning of the system. Continue reading ‘Virioplankton and bacterioplankton in a shallow CO2-dominated hydrothermal vent (Panarea Island, Tyrrhenian Sea)’

The rise of harmful cyanobacteria blooms: The potential roles of eutrophication and climate change

Cyanobacteria are the most ancient phytoplankton on the planet and form harmful algal blooms in freshwater, estuarine, and marine ecosystems. Recent research suggests that eutrophication and climate change are two processes that may promote the proliferation and expansion of cyanobacterial harmful algal blooms. In this review, we specifically examine the relationships between eutrophication, climate change and representative cyanobacteriagenera from freshwater (Microcystis, Anabaena, Cylindrospermopsis), estuarine (Nodularia, Aphanizomenon), and marine ecosystems (Lyngbya, Synechococcus, Trichodesmium). Commonalities among cyanobacteria genera include being highly competitive for low concentrations of inorganic P (DIP) and the ability to acquire organic P compounds. Both diazotrophic (= nitrogen (N2) fixers) and non-diazotrophic cyanobacteria display great flexibility in the N sources they exploit to form blooms. Hence, while some cyanobacterial blooms are associated with eutrophication, several form blooms when concentrations of inorganic N and P are low. Cyanobacteria dominate phytoplankton assemblages under higher temperatures due to both physiological (e.g. more rapid growth) and physical factors (e.g. enhanced stratification), with individual species showing different temperature optima. Significantly less is known regarding how increasing carbon dioxide (CO2) concentrations will affect cyanobacteria, although some evidence suggests several genera of cyanobacteria are well-suited to bloom under low concentrations of CO2. While the interactive effects of future eutrophication and climate change on harmful cyanobacterial blooms are complex, much of the current knowledge suggests these processes are likely to enhance the magnitude and frequency of these events.
Continue reading ‘The rise of harmful cyanobacteria blooms: The potential roles of eutrophication and climate change’

“Bottom up” ocean acidification: A study on the effects of CO2 on the bacterial community in sediments

As atmospheric concentration of CO2 continues to increase, alternatives on how to mitigate and reduce the rate of this development has received much attention. Carbon Capture and Storage (CCS) is doing just this by storing CO2 that ordinarily would have been emitted into the atmosphere. By storing the CO2 in geological storages it is isolated for a long period of time, thousands of years. Even though this type of storage is considered safe and the risk of leakage small, one can never be absolutely sure of it holding. The risk of large leakages is considered negligible, but the risk of relative small leakages is uncertain. If such a small leakage were to occur, what are the consequences and how such a leakage could be detected? These are difficult questions to answer, but the need to be able eventually answer them is important, especially considering that international guidelines (London protocol and OSPAR) has been developed so that these questions can be answered, and they eventually need to be followed. The long term aims of this project are to developing monitoring and detection methods for small leakages and assess the environmental impacts of this type of leakage.
Continue reading ‘“Bottom up” ocean acidification: A study on the effects of CO2 on the bacterial community in sediments’

Interactions between CCM and N2 fixation in Trichodesmium

In view of the current increase in atmospheric pCO2 and concomitant changes in the marine environment, it is crucial to assess, understand, and predict future responses of ecologically relevant phytoplankton species. The diazotrophic cyanobacterium Trichodesmium erythraeum was found to respond strongly to elevated pCO2 by increasing growth, production rates, and N2 fixation. The magnitude of these CO2 effects exceeds those previously seen in other phytoplankton, raising the question about the underlying mechanisms. Here, we review recent publications on metabolic pathways of Trichodesmium from a gene transcription level to the protein activities and energy fluxes. Diurnal patterns of nitrogenase activity change markedly with CO2 availability, causing higher diel N2 fixation rates under elevated pCO2. The observed responses to elevated pCO2 could not be attributed to enhanced energy generation via gross photosynthesis, although there are indications for CO2-dependent changes in ATP/NADPH + H+ production. The CO2 concentrating mechanism (CCM) in Trichodesmium is primarily based on HCO3 uptake. Although only little CO2 uptake was detected, the NDH complex seems to play a crucial role in internal cycling of inorganic carbon, especially under elevated pCO2. Affinities for inorganic carbon change over the day, closely following the pattern in N2 fixation, and generally decrease with increasing pCO2. This down-regulation of CCM activity and the simultaneously enhanced N2 fixation point to a shift in energy allocation from carbon acquisition to N2 fixation under elevated pCO2 levels. A strong light modulation of CO2 effects further corroborates the role of energy fluxes as a key to understand the responses of Trichodesmium.
Continue reading ‘Interactions between CCM and N2 fixation in Trichodesmium’

Global declines in oceanic nitrification rates as a consequence of ocean acidification

Ocean acidification produced by dissolution of anthropogenic carbon dioxide (CO(2)) emissions in seawater has profound consequences for marine ecology and biogeochemistry. The oceans have absorbed one-third of CO(2) emissions over the past two centuries, altering ocean chemistry, reducing seawater pH, and affecting marine animals and phytoplankton in multiple ways. Microbially mediated ocean biogeochemical processes will be pivotal in determining how the earth system responds to global environmental change; however, how they may be altered by ocean acidification is largely unknown. We show here that microbial nitrification rates decreased in every instance when pH was experimentally reduced (by 0.05-0.14) at multiple locations in the Atlantic and Pacific Oceans. Nitrification is a central process in the nitrogen cycle that produces both the greenhouse gas nitrous oxide and oxidized forms of nitrogen used by phytoplankton and other microorganisms in the sea; at the Bermuda Atlantic Time Series and Hawaii Ocean Time-series sites, experimental acidification decreased ammonia oxidation rates by 38% and 36%. Ammonia oxidation rates were also strongly and inversely correlated with pH along a gradient produced in the oligotrophic Sargasso Sea (r(2) = 0.87, P < 0.05). Across all experiments, rates declined by 8-38% in low pH treatments, and the greatest absolute decrease occurred where rates were highest off the California coast. Collectively our results suggest that ocean acidification could reduce nitrification rates by 3-44% within the next few decades, affecting oceanic nitrous oxide production, reducing supplies of oxidized nitrogen in the upper layers of the ocean, and fundamentally altering nitrogen cycling in the sea.

Continue reading ‘Global declines in oceanic nitrification rates as a consequence of ocean acidification’

Phytoplankton-bacteria coupling under elevated CO2 levels: a stable isotope labelling study

The potential impact of rising carbon dioxide (CO2) on carbon transfer from phytoplankton to bacteria was investigated during the 2005 PeECE III mesocosm study in Bergen, Norway. Sets of mesocosms, in which a phytoplankton bloom was induced by nutrient addition, were incubated under 1× (~350 μatm), 2× (~700 μatm), and 3× present day CO2 (~1050 μatm) initial seawater and sustained atmospheric CO2 levels for 3 weeks. 13C labelled bicarbonate was added to all mesocosms to follow the transfer of carbon from dissolved inorganic carbon (DIC) into phytoplankton and subsequently heterotrophic bacteria, and settling particles. Isotope ratios of polar-lipid-derived fatty acids (PLFA) were used to infer the biomass and production of phytoplankton and bacteria. Phytoplankton PLFA were enriched within one day after label addition, whilst it took another 3 days before bacteria showed substantial enrichment. Group-specific primary production measurements revealed that coccolithophores showed higher primary production than green algae and diatoms. Elevated CO2 had a significant positive effect on post-bloom biomass of green algae, diatoms, and bacteria. A simple model based on measured isotope ratios of phytoplankton and bacteria revealed that CO2 had no significant effect on the carbon transfer efficiency from phytoplankton to bacteria during the bloom. There was no indication of CO2 effects on enhanced settling based on isotope mixing models during the phytoplankton bloom, but this could not be determined in the post-bloom phase. Our results suggest that CO2 effects are most pronounced in the post-bloom phase, under nutrient limitation.
Continue reading ‘Phytoplankton-bacteria coupling under elevated CO2 levels: a stable isotope labelling study’

Calcium carbonate precipitation induced by the growth of the marine cyanobacteria Trichodesmium

In this laboratory study, we monitored the buildup of biomass and concomitant shift in seawater carbonate chemistry over the course of a Trichodesmium bloom under different phosphorus (P) availability. During exponential growth, dissolved inorganic carbon (DIC) decreased, while pH increased until maximum cell densities were reached. Once P became depleted, DIC decreased even further and total alkalinity (TA) dropped, accompanied by precipitation of aragonite. Under P-replete conditions, DIC increased and TA remained constant in the postbloom phase. A diffusion-reaction model was employed to estimate changes in carbonate chemistry of the diffusive boundary layer. This study demonstrates that Trichodesmium can induce precipitation of aragonite from seawater and further provides possible explanations about underlying mechanisms.
Continue reading ‘Calcium carbonate precipitation induced by the growth of the marine cyanobacteria Trichodesmium’

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Ocean acidification in the IPCC AR5 WG II

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