Ecological Interaction between Bacteriophages and Bacteria in Sub-Arctic Kongsfjorden Bay, Svalbard, Norway.

Marine virus diversity and their relationships with their hosts in the marine environment remain unclear. This study investigated the co-occurrence of marine DNA bacteriophages (phages) and bacteria in the sub-Arctic area of Kongsfjorden Bay in Svalbard (Norway) in April and June 2018 using metagenomics tools. Of the marine viruses identified, 48-81% were bacteriophages of the families Myoviridae, Siphoviridae, and Podoviridae. Puniceispirillum phage HMO-2011 was dominant (7.61%) in April, and Puniceispirillum phage HMO-2011 (3.32%) and Pelagibacter phage HTVC008M (3.28%) were dominant in June. Gammaproteobacteria (58%), including Eionea flava (14.3%) and Pseudomonas sabulinigri (12.2%), were dominant in April, whereas Alphaproteobacteria (87%), including Sulfitobacter profundi (51.5%) and Loktanella acticola (32.4%), were dominant in June. The alpha diversity of the bacteriophages and bacterial communities exhibited opposite patterns. The diversity of the bacterial community was higher in April and lower in June. Changes in water temperature and light can influence the relationship between bacteria and bacteriophages.

Covariance of Marine Nucleocytoplasmic Large DNA Viruses with Eukaryotic Plankton Communities in the Sub-Arctic Kongsfjorden Ecosystem: A Metagenomic Analysis of Marine Microbial Ecosystems.

Nucleocytoplasmic large DNA viruses (NCLDVs) infect various marine eukaryotes. However, little is known about NCLDV diversity and their relationships with eukaryotic hosts in marine environments, the elucidation of which will advance the current understanding of marine ecosystems. This study characterizes the interplay between NCLDVs and the eukaryotic plankton community (EPC) in the sub-Arctic area using metagenomics and metabarcoding to investigate NCLDVs and EPC, respectively, in the Kongsfjorden ecosystem of Svalbard (Norway) in April and June 2018. Gyrodinium helveticum (Dinophyceae) is the most prevalent eukaryotic taxon in the EPC in April, during which time Mimiviridae (31.8%), Poxviridae (25.1%), Phycodnaviridae (14.7%) and Pandoraviridae (13.1%) predominate. However, in June, the predominant taxon is Aureococcus anophagefferens (Pelagophyceae), and the NCLDVs, Poxviridae (32.9%), Mimiviridae (29.1%), and Phycodnaviridae (18.5%) appear in higher proportions with an increase in Pelagophyceae, Bacillariophyceae, and Chlorophyta groups. Thus, differences in NCLDVs may be caused by changes in EPC composition in response to environmental changes, such as increases in water temperature and light intensity. Taken together, these findings are particularly relevant considering the anticipated impact of NCLDV-induced EPC control mechanisms on polar regions and, therefore, improve the understanding of the Sub-Arctic Kongsfjorden ecosystem.

Spatial distribution and origin of organic matters in an Arctic fjord system based on lipid biomarkers (n-alkanes and sterols).

The concentration of n-alkanes (C17-C35) and sterols in marine particulate matter were investigated to trace the origin of organic carbon in Kongsfjorden in early spring (April). The spatial distributions of environmental factors (seawater temperature, salinity, density, turbidity, chlorophyll a (chl. a) and particulate organic carbon (POC) concentrations) and the cell density of phytoplankton differed between the inner and outer fjord regions. In addition, brassicasterol, diatom biomarker, showed a high concentration in the outer fjord and positive correlations with the chl. a and POC concentrations in the water column. In contrast, some sterols originating from terrestrial organic matter (OM), such as stigmasterol and campesterol, showed relatively higher concentrations in the inner fjord than in the outer fjord. Based on the distance-based redundancy analysis (db-RDA) result, the distributions of organic compounds are predominantly controlled by the water density and the POC and chl. a concentrations, and these distributions allowed us to divide the inner and outer fjord regions. However, the hierarchical clustering of principal components (HCPC) results obtained based on principal component analysis (PCA) using lipid biomarkers (C17-C35 alkanes and sterols) and environmental factors indicated that the clusters were distinguished by surface (0 m) and subsurface (>4 m) seawater samples rather than by any regional division. Notably, the concentration of relatively short-chain alkanes (average chain length (ACL): 24.6 ± 3.7) without a carbon preference for odd numbers (carbon preference index (CPI): 0.97 ± 0.11) in the sea surface layer was significantly higher than that of subsurface seawater (ACL: 31.1 ± 0.5 and CPI: 1.06 ± 0.03) in the early spring. This suggests the potential of these compounds as indicators for tidewater glacier-derived OM and freshwater input by snow melt into the fjord system. Hence, these results demonstrate that the distributions of lipid biomarkers in the water column possibly provide important information for a comprehensive understanding of the origin and transport of OM in an Arctic fjord.

Dynamic bacterial community response to Akashiwo sanguinea (Dinophyceae) bloom in indoor marine microcosms.

We investigated the dynamics of the bacterial composition and metabolic function within Akashiwo sanguinea bloom using a 100-L indoor microcosm and metagenomic next-generation sequencing. We found that the bacterial community was classified into three groups at 54% similarity. Group I was associated with "during the A. sanguinea bloom stage" and mainly consisted of Alphaproteobacteria, Flavobacteriia and Gammaproteobacteria. Meanwhile, groups II and III were associated with the "late bloom/decline stage to post-bloom stage" with decreased Flavobacteriia and Gammaproteobacteria in these stages. Upon the termination of the A. sanguinea bloom, the concentrations of inorganic nutrients (particularly PO43-, NH4+ and dissolved organic carbon) increased rapidly and then decreased. From the network analysis, we found that the A. sanguinea node is associated with certain bacteria. After the bloom, the specific increases in NH4+ and PO43- nodes are associated with other bacterial taxa. The changes in the functional groups of the bacterial community from chemoheterotrophy to nitrogen association metabolisms were consistent with the environmental impacts during and after A. sanguinea bloom. Consequently, certain bacterial communities and the environments dynamically changed during and after harmful algal blooms and a rapid turnover within the bacterial community and their function can respond to ecological interactions.

Zooming on dynamics of marine microbial communities in the phycosphere of Akashiwo sanguinea (Dinophyta) blooms.

Characterizing ecological relationships between viruses, bacteria and phytoplankton in the ocean is critical to understanding the ecosystem; however, these relationships are infrequently investigated together. To understand the dynamics of microbial communities and environmental factors in harmful algal blooms (HABs), we examined the environmental factors and microbial communities during Akashiwo sanguinea HABs in the Jangmok coastal waters of South Korea by metagenomics. Specific bacterial species showed complex synergistic and antagonistic relationships with the A. sanguinea bloom. The endoparasitic dinoflagellate Amoebophrya sp. 1 controlled the bloom dynamics and correlated with HAB decline. Among nucleocytoplasmic large DNA viruses (NCLDVs), two Pandoraviruses and six Phycodnaviruses were strongly and positively correlated with the HABs. Operational taxonomic units of microbial communities and environmental factors associated with A. sanguinea were visualized by network analysis: A. sanguinea-Amoebophrya sp. 1 (r = .59, time lag: 2 days) and A. sanguinea-Ectocarpus siliculosus virus 1 in Phycodnaviridae (0.50, 4 days) relationships showed close associations. The relationship between A. sanguinea and dissolved inorganic phosphorus relationship also showed a very close correlation (0.74, 0 day). Microbial communities and the environment changed dynamically during the A. sanguinea bloom, and the rapid turnover of microorganisms responded to ecological interactions. A. sanguinea bloom dramatically changes the environments by exuding dissolved carbohydrates via autotrophic processes, followed by changes in microbial communities involving host-specific viruses, bacteria and parasitoids. Thus, the microbial communities in HAB are composed of various organisms that interact in a complex manner.

Latitudinal Distributions and Controls of Bacterial Community Composition during the Summer of 2017 in Western Arctic Surface Waters (from the Bering Strait to the Chukchi Borderland).

The western Arctic Ocean is experiencing some of the most rapid environmental changes in the Arctic. However, little is known about the microbial community response to these changes. Employing observations from the summer of 2017, this study investigated latitudinal variations in bacterial community composition in surface waters between the Bering Strait and Chukchi Borderland and the factors driving the changes. Results indicate three distinctive communities. Southern Chukchi bacterial communities are associated with nutrient rich conditions, including genera such as Sulfitobacter, whereas the northern Chukchi bacterial community is dominated by SAR clades, Flavobacterium, Paraglaciecola, and Polaribacter genera associated with low nutrients and sea ice conditions. The frontal region, located on the boundary between the southern and northern Chukchi, is a transition zone with intermediate physical and biogeochemical properties; however, bacterial communities differed markedly from those found to the north and south. In the transition zone, Sphingomonas, with as yet undetermined ecological characteristics, are relatively abundant. Latitudinal distributions in bacterial community composition are mainly attributed to physical and biogeochemical characteristics, suggesting that these communities are susceptible to Arctic environmental changes. These findings provide a foundation to improve understanding of bacterial community variations in response to a rapidly changing Arctic Ocean.

Potential Implications of Changing Photosynthetic End-Products of Phytoplankton Caused by Sea Ice Conditions in the Northern Chukchi Sea.

The recent dramatic decline in sea ice conditions in the Arctic Ocean has led to the ecophysiological changes in the phytoplankton community. Little is currently known about how the physiological status of phytoplankton has changed under rapidly changing environmental conditions in the Arctic Ocean. Using the 13C isotope tracer technique, the carbon allocation of phytoplankton into different photosynthetic end-products was determined in the northern Chukchi Sea on the basis of two Arctic expeditions conducted in 2011 and 2012 to identify the physiological status of phytoplankton. Lipids were the predominant photosynthetic biochemical fraction (42.5%) in 2011, whereas carbon allocation to proteins was most dominant under ice-free conditions in 2012 (47.7%). Based on a comparison of the photosynthetic carbon allocation of phytoplankton according to sea ice conditions, we found that photosynthetic carbon allocation to different macromolecular pools was significantly different depending on the sea ice conditions and that the light conditions caused by different sea ice conditions could be an important reason for the differences in carbon allocation to photosynthetic end-products. Different dominant phytoplankton groups related to size classes also could cause changes in the photosynthetic carbon allocation of phytoplankton related mainly to the lipid synthesis. Our results showed that the physiological status of Arctic phytoplankton could be changed by producing different photosynthetic end-products under current environmental changes. This change in photosynthetic end-products of phytoplankton as a basic food source could be further linked to higher trophic levels in regards to their nutritional and energetic aspects, which could have potential consequences for Arctic marine ecosystems.