Monitoring of Arctic sea ice algae and open water phytoplankton : impact of photooxidative, chemical and salinity stress on associated bacteria and its implication on its preservation and its contribution to the sediments

Les milieux arctiques sont menacés par le réchauffement global. La perspective d’une disparition totale de la banquise d’ici 2050 pose d’importantes questions quant au devenir de ces écosystèmes. Premiers maillons de la chaîne alimentaire, les algues de glace jouent un rôle capital dans le fonctionnement de ces milieux. De par leur chute rapide et la faible activité des bactéries dans ces eaux, les algues de glace contribuent à l’export du carbone vers les sédiments. Dans cette étude, nous nous sommes intéressés à l’impact de l’état physiologique des bactéries associées aux algues de glace et des différents stress subits par ces dernières sur le devenir du matériel algal. Si nos résultats ont démontré l’importance des stress halin, chimique et photochimique sur le mauvais état physiologique des bactéries associées aux algues de glace, les interactions trophiques au sein de la glace restent complexes et l’impact du réchauffement global sur ces dernières reste à investiguer.Arctic environments are highly endangered by global warming. The view of ice-free waters by 2050 raises important questions about the future of these ecosystems. Ice algae are the roots of the Arctic food chain and play a crucial role in the functioning of these environments. Because of their rapid fall and the low biodegradation activity of bacteria in these waters, ice algae contribute to the export of CO2 to the sediments. This study focuses on the effects of the physiological state of the bacteria associated with ice algae and the different stresses they undergo on the fate of the algal material. If our results showed the importance of haline, chemical and photochemical stresses on the poor physiological state of bacteria associated with ice algae, trophic interactions within the ice remain complex and the impact of global warming on them still needs to be investigated

Use of Stress Signals of Their Attached Bacteria to Monitor Sympagic Algae Preservation in Canadian Arctic Sediments

Based on the strong aggregation of sympagic (ice-associated) algae and the high mortality or inactivity of bacteria attached to them, it was previously hypothesized that sympagic algae should be significant contributors to the export of carbon to Arctic sediments. In the present work, the lipid content of 30 sediment samples collected in the Canadian Arctic was investigated to test this hypothesis. The detection of high proportions of trans vaccenic fatty acid (resulting from cis-trans isomerase (CTI) activity of bacteria under hypersaline conditions) and 10S-hydroxyhexadec-8(trans)-enoic acid (resulting from 10S-DOX bacterial detoxification activity in the presence of deleterious free palmitoleic acid) confirmed: (i) the strong contribution of sympagic material to some Arctic sediments, and (ii) the impaired physiological status of its associated bacterial communities. Unlike terrestrial material, sympagic algae that had escaped zooplanktonic grazing appeared relatively preserved from biotic degradation in Arctic sediments. The expected reduction in sea ice cover resulting from global warming should cause a shift in the relative contributions of ice-associated vs. pelagic algae to the seafloor, and thus to a strong modification of the carbon cycl

Use of Stress Signals of Their Attached Bacteria to Monitor Sympagic Algae Preservation in Canadian Arctic Sediments

Based on the strong aggregation of sympagic (ice-associated) algae and the high mortality or inactivity of bacteria attached to them, it was previously hypothesized that sympagic algae should be significant contributors to the export of carbon to Arctic sediments. In the present work, the lipid content of 30 sediment samples collected in the Canadian Arctic was investigated to test this hypothesis. The detection of high proportions of trans vaccenic fatty acid (resulting from cis-trans isomerase (CTI) activity of bacteria under hypersaline conditions) and 10S-hydroxyhexadec-8(trans)-enoic acid (resulting from 10S-DOX bacterial detoxification activity in the presence of deleterious free palmitoleic acid) confirmed: (i) the strong contribution of sympagic material to some Arctic sediments, and (ii) the impaired physiological status of its associated bacterial communities. Unlike terrestrial material, sympagic algae that had escaped zooplanktonic grazing appeared relatively preserved from biotic degradation in Arctic sediments. The expected reduction in sea ice cover resulting from global warming should cause a shift in the relative contributions of ice-associated vs. pelagic algae to the seafloor, and thus to a strong modification of the carbon cycle

Singlet oxygen‐induced alteration of bacteria associated with phytodetritus: Effect of irradiance

International audienceContrasting irradiation of senescent cells of the diatom Thalassiosira sp. in association with the bacterium Pseudomonas stutzeri showed the effect of intensity of irradiance on the transfer of singlet oxygen ( 1 O 2 ) to bacteria attached to phytoplanktonic cells. Under low irradiances, 1 O 2 is produced slowly, favors the oxidation of algal unsaturated lipids (photodynamic effect), and limits 1 O 2 transfer to attached bacteria. However, high irradiances induce a rapid and intense production of 1 O 2 , which diffuses out of the chloroplasts and easily reaches the attached bacteria, where it efficiently oxidizes their unsaturated membrane components. Analysis of numerous sinking particle samples collected in different regions of the Canadian Arctic showed that the photooxidation state of attached bacteria increased from ice‐covered areas to open water, in agreement with in vitro results. Photooxidation of bacteria appeared to be particularly intense in sea ice, where the sympagic algae–bacteria association is maintained at relatively high irradiances for long periods of time

Singlet oxygen-induced alteration of bacteria associated with phytodetritus: effect of bacterial pigments

We sought to determine whether the presence of carotenoids actively protects bacteria associated with senescent phytoplankton cells from damage caused by singlet oxygen (1O2) resulting from the cessation of photosynthetic reactions. We irradiated senescent cells of the diatom Thalassiosira sp. associated with the bacterial strains Pseudomonas stutzeri (a ubiquitous planktonic unpigmented heterotrophic bacterium) or Dinoroseobacter shibae (an aerobic anoxygenic bacterium often associated with phytoplankton rich in the spheroidenone, carotenoid). The analysis focused on the photooxidation of bacterial membrane lipids (vaccenic acid) and the expression of genes involved in DNA repair systems. In P. stutzeri cells, 1O2 transferred from senescent algae was not completely scavenged by bacterial membrane MUFAs and reached the cytoplasm, allowing both 1O2 and UV radiation to cause DNA damage. In D. shibae, scavenging by bacterial membrane MUFAs quenching by spheroidenone allowed only a small fraction of 1O2 to reach the cytoplasm, where the efficient detoxifying activity of mutY limited their impact on the DNA of this strain, thus preventing oxidative stress. The fact that Rhodobacteriales is the dominant order in bacterioplankton communities associated with algal blooms could thus be due to the protective effect of its constituent carotenoids against 1O2- and UV-induced damage

Stress factors resulting from the Arctic vernal sea-ice melt

International audienceDuring sea-ice melt in the Arctic, primary production by sympagic (sea-ice) algae can be exported efficiently to the seabed if sinking rates are rapid and activities of associated heterotrophic bacteria are limited. Salinity stress due to melting ice has been suggested to account for such low bacterial activity. We further tested this hypothesis by analyzing samples of sea ice and sinking particles collected from May 18 to June 29, 2016, in western Baffin Bay as part of the Green Edge project. We applied a method not previously used in polar regions—quantitative PCR coupled to the propidium monoazide DNA-binding method—to evaluate the viability of bacteria associated with sympagic and sinking algae. We also measured cis-trans isomerase activity, known to indicate rapid bacterial response to salinity stress in culture studies, as well as free fatty acids known to be produced by algae as bactericidal compounds. The viability of sympagic-associated bacteria was strong in May (only approximately 10% mortality of total bacteria) and weaker in June (average mortality of 43%; maximum of 75%), with instances of elevated mortality in sinking particle samples across the time series (up to 72%). Short-term stress reflected by cis-trans isomerase activity was observed only in samples of sinking particles collected early in the time series. Following snow melt, however, and saturating levels of photosynthetically active radiation in June, we observed enhanced ice-algal production of bactericidal compounds (free palmitoleic acid; up to 4.8 mg L–1). We thus suggest that protection of sinking sympagic material from bacterial degradation early in a melt season results from low bacterial activity due to salinity stress, while later in the season, algal production of bactericidal compounds induces bacterial mortality. A succession of bacterial stressors during Arctic ice melt helps to explain the efficient export of sea-ice algal material to the seabed

Viability and stress state of bacteria associated with primary production or zooplankton-derived suspended particulate matter in summer along a transect in Baffin Bay (Arctic Ocean)

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Soil, plant and red mud: Case study of two deposits in Provence

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Soil, plant and red mud: Case study of two deposits in Provence

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Soil, plant and red mud: Case study of two deposits in Provence

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