scholarly journals How Microbial Food Web Interactions Shape the Arctic Ocean Bacterial Community Revealed by Size Fractionation Experiments

2021 ◽  
Vol 9 (11) ◽  
pp. 2378
Author(s):  
Oliver Müller ◽  
Lena Seuthe ◽  
Bernadette Pree ◽  
Gunnar Bratbak ◽  
Aud Larsen ◽  
...  
Keyword(s):  
Bacterial Community ◽  
Food Web ◽  
Community Composition ◽  
Seasonal Changes ◽  
Bacterial Community Composition ◽  
Trophic Levels ◽  
The Arctic ◽  
Microbial Food Web ◽  
Small Scale ◽  
Size Fractionation

In the Arctic, seasonal changes are substantial, and as a result, the marine bacterial community composition and functions differ greatly between the dark winter and light-intensive summer. While light availability is, overall, the external driver of the seasonal changes, several internal biological interactions structure the bacterial community during shorter timescales. These include specific phytoplankton–bacteria associations, viral infections and other top-down controls. Here, we uncover these microbial interactions and their effects on the bacterial community composition during a full annual cycle by manipulating the microbial food web using size fractionation. The most profound community changes were detected during the spring, with ‘mutualistic phytoplankton’—Gammaproteobacteria interactions dominating in the pre-bloom phase and ‘substrate-dependent phytoplankton’—Flavobacteria interactions during blooming conditions. Bacterivores had an overall limited effect on the bacterial community composition most of the year. However, in the late summer, grazing was the main factor shaping the community composition and transferring carbon to higher trophic levels. Identifying these small-scale interactions improves our understanding of the Arctic marine microbial food web and its dynamics.

scholarly journals Increasing addition of autochthonous to allochthonous carbon in nutrient-rich aquatic systems stimulates carbon consumption but does not alter bacterial community composition

2013 ◽  
Vol 10 (8) ◽  
pp. 14261-14300 ◽  
Author(s):  
K. Attermeyer ◽  
T. Hornick ◽  
Z. E. Kayler ◽  
A. Bahr ◽  
E. Zwirnmann ◽  
...  
Keyword(s):  
Bacterial Community ◽  
Community Composition ◽  
Temporal Dynamics ◽  
Heterotrophic Bacteria ◽  
Dissolved Inorganic Carbon ◽  
Bacterial Community Composition ◽  
Trophic Levels ◽  
Aquatic Systems ◽  
Chemical Quality ◽  
Carbon Consumption

Abstract. Dissolved organic carbon (DOC) concentrations – mainly of terrestrial origin – are increasing worldwide in inland waters. The biodegradability of the DOC varies depending on quantity and chemical quality. Heterotrophic bacteria are the main consumers of DOC and thus determine DOC temporal dynamics and availability for higher trophic levels. It is therefore crucial to understand the processes controlling the bacterial turnover of additional allochthonous and autochthonous DOC in aquatic systems. Our aim was to study bacterial carbon (C) turnover with respect to DOC quantity and chemical quality using both allochthonous and autochthonous DOC sources. We incubated a natural bacterial community with allochthonous C (13C-labeled beech leachate) and increased concentrations and pulses (intermittent occurrence of organic matter input) of autochthonous C (algae lysate). We then determined bacterial carbon consumption, activities, and community composition together with the carbon flow through bacteria using stable C isotopes. The chemical analysis of single sources revealed differences in aromaticity and fractions of low and high molecular weight substances (LMWS and HMWS, respectively) between allochthonous and autochthonous C sources. In parallel to these differences in chemical composition, we observed a higher availability of allochthonous C as evidenced by increased DOC consumption and bacterial growth efficiencies (BGE) when solely allochthonous C was provided. In treatments with mixed sources, rising concentrations of added autochthonous DOC resulted in a further, significant increase in bacterial DOC consumption from 52 to 68% when nutrients were not limiting. This rise was accompanied by a decrease in the humic substances (HS) fraction and an increase in bacterial biomass. Stable C isotope analyses of phospholipid fatty acids (PLFA) and respired dissolved inorganic carbon (DIC) supported a preferential assimilation of autochthonous C and respiration of the allochthonous C. Changes in DOC concentration and consumption in mixed treatments did not affect bacterial community composition (BCC), but BCC differed in single vs. mixed incubations. Our study highlights that DOC quantity affects bacterial C consumption but not BCC in nutrient-rich aquatic systems. BCC shifted when a mixture of allochthonous and autochthonous C was provided simultaneously to the bacterial community. Our results indicate that chemical quality rather than source of DOC per se (allochthonous vs. autochthonous) determines bacterial DOC turnover.

scholarly journals Enhanced bacterial decomposition with increasing addition of autochthonous to allochthonous carbon without any effect on bacterial community composition

2014 ◽  
Vol 11 (6) ◽  
pp. 1479-1489 ◽  
Author(s):  
K. Attermeyer ◽  
T. Hornick ◽  
Z. E. Kayler ◽  
A. Bahr ◽  
E. Zwirnmann ◽  
...  
Keyword(s):  
Bacterial Community ◽  
Community Composition ◽  
Temporal Dynamics ◽  
Heterotrophic Bacteria ◽  
Bacterial Community Composition ◽  
Bacterial Biomass ◽  
Trophic Levels ◽  
Bacterial Growth Efficiency ◽  
Chemical Quality ◽  
Bacterial C

Abstract. Dissolved organic carbon (DOC) concentrations – mainly of terrestrial origin – are increasing worldwide in inland waters. Heterotrophic bacteria are the main consumers of DOC and thus determine DOC temporal dynamics and availability for higher trophic levels. Our aim was to study bacterial carbon (C) turnover with respect to DOC quantity and chemical quality using both allochthonous and autochthonous DOC sources. We incubated a natural bacterial community with allochthonous C (13C-labeled beech leachate) and increased concentrations and pulses (intermittent occurrence of organic matter input) of autochthonous C (phytoplankton lysate). We then determined bacterial C consumption, activities, and community composition together with the C flow through bacteria using stable C isotopes. The chemical analysis of single sources revealed differences in aromaticity and low- and high-molecular-weight substance fractions (LMWS and HMWS, respectively) between allochthonous and autochthonous C sources. Both DOC sources (allochthonous and autochthonous DOC) were metabolized at a high bacterial growth efficiency (BGE) around 50%. In treatments with mixed sources, rising concentrations of added autochthonous DOC resulted in a further, significant increase in bacterial DOC consumption of up to 68% when nutrients were not limiting. This rise was accompanied by a decrease in the humic substance (HS) fraction and an increase in bacterial biomass. Changes in DOC concentration and consumption in mixed treatments did not affect bacterial community composition (BCC), but BCC differed in single vs. mixed incubations. Our study highlights that DOC quantity affects bacterial C consumption but not BCC in nutrient-rich aquatic systems. BCC shifted when a mixture of allochthonous and autochthonous C was provided simultaneously to the bacterial community. Our results indicate that chemical quality rather than source of DOC per se (allochthonous vs. autochthonous) determines bacterial DOC turnover.

scholarly journals Use of organic exudates from two polar diatoms by bacterial isolates from the Arctic Ocean

2020 ◽  
Vol 378 (2181) ◽  
pp. 20190356 ◽  
Author(s):  
Lucas Tisserand ◽  
Laëtitia Dadaglio ◽  
Laurent Intertaglia ◽  
Philippe Catala ◽  
Christos Panagiotopoulos ◽  
...  
Keyword(s):  
Bacterial Community ◽  
Sea Ice ◽  
Arctic Ocean ◽  
Community Composition ◽  
Bacterial Community Composition ◽  
Model Systems ◽  
The Arctic ◽  
Bacterial Strains ◽  
Biological Communities ◽  
Polar Diatoms

Global warming affects primary producers in the Arctic, with potential consequences for the bacterial community composition through the consumption of microalgae-derived dissolved organic matter (DOM). To determine the degree of specificity in the use of an exudate by bacterial taxa, we used simple microalgae–bacteria model systems. We isolated 92 bacterial strains from the sea ice bottom and the water column in spring–summer in the Baffin Bay (Arctic Ocean). The isolates were grouped into 42 species belonging to Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes. Forty strains were tested for their capacity to grow on the exudate from two Arctic diatoms . Most of the strains tested (78%) were able to grow on the exudate from the pelagic diatom Chaetoceros neogracilis , and 33% were able to use the exudate from the sea ice diatom Fragilariopsis cylindrus . 17.5% of the strains were not able to grow with any exudate, while 27.5% of the strains were able to use both types of exudates. All strains belonging to Flavobacteriia ( n  = 10) were able to use the DOM provided by C. neogracilis , and this exudate sustained a growth capacity of up to 100 times higher than diluted Marine Broth medium, of two Pseudomonas sp. strains and one Sulfitobacter strain. The variable bioavailability of exudates to bacterial strains highlights the potential role of microalgae in shaping the bacterial community composition. This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

scholarly journals How trophic cascades and photic zone nutrient content interact to generate basin-scale differences in the microbial food web

2020 ◽  
Vol 77 (5) ◽  
pp. 1639-1647 ◽  
Author(s):  
T Frede Thingstad
Keyword(s):  
Food Web ◽  
Food Webs ◽  
Trophic Cascades ◽  
Trophic Levels ◽  
Seasonal Migration ◽  
The Arctic ◽  
Microbial Food Web ◽  
Food Chains ◽  
Basin Scale ◽  
The Mediterranean

Abstract In linear food chains, resource and predator control produce positive and negative correlations, respectively, between biomass at adjacent trophic levels. These simple relationships become more complex in food webs that contain alternative food chains of unequal lengths. We have used a “minimum” model for the microbial part of the pelagic food web that has three such food chains connecting free mineral nutrients to copepods: via diatoms, autotrophic flagellates, and heterotrophic bacteria. Trophic cascades from copepods strongly modulates the balance between the three pathways and, therefore, the functionality of the microbial food web in services such as food production for higher trophic levels, DOM degradation, and ocean carbon sequestration. The result is a theoretical framework able to explain, not only apparent conflicts in Arctic mesocosm experiments, but also biogeochemical features of the Mediterranean. Here, the fundamental difference between Arctic and Mediterranean microbial food webs is the way they are predator driven by seasonal migration of large copepods in the Arctic, but resource driven due to the anti-estuarine circulation in the Mediterranean. In this framework, global change effects on microbial ecosystem functions are more like to come indirectly through changes in these drivers than through direct temperature effects on the microbes.

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