Bacterioplankton communities of Crater Lake,OR: dynamic changes with euphotic zone food web structure and stable deep water populations

The distribution of bacterial and archaeal species in Crater Lake plankton varies dramatically over depth and with time, as assessed by hybridization of group-specific oligonucleotides to RNA extracted from lakewater. Nonmetric, multidimensional scaling (MDS) analysis of relative bacterial phylotype densities revealed complex relationships among assemblages sampled from depth profiles in July, August and September of 1997 through 1999. CL500-11 green nonsulfur bacteria (Phylum Chloroflexi) and marine Group I crenarchaeota are consistently dominant groups in the oxygenated deep waters at 300 and 500 m. Other phylotypes found in the deep waters are similar to surface and mid-depth populations and vary with time. Euphotic zone assemblages are dominated either by β-proteobacteria or CL120-10 verrucomicrobia, and ACK4 actinomycetes. MDS analyses of euphotic zone populations in relation to environmental variables and phytoplankton and zooplankton population structures reveal apparent links between Daphnia pulicaria zooplankton population densities and microbial community structure. These patterns may reflect food web interactions that link kokanee salmon population densities to community structure of the bacterioplankton, via fish predation on Daphnia with cascading consequences to Daphnia bacterivory and predation on bacterivorous protists. These results demonstrate a stable bottom-water microbial community. They also extend previous observations of food web-driven changes in euphotic zone bacterioplankton community structure to an oligotrophic setting.     

Biogeography and Host Fidelity of Bacterial Communities in Ircinia spp. from the Bahamas

Research on sponge microbial assemblages has revealed different trends in the geographic variability and specificity of bacterial symbionts. Here, we combined replicated terminal-restriction fragment length polymorphism (T-RFLP) and clone library analyses of 16S rRNA gene sequences to investigate the biogeographic and host-specific structure of bacterial communities in two congeneric and sympatric sponges: Ircinia strobilina, two color morphs of Ircinia felix and ambient seawater. Samples were collected from five islands of the Bahamas separated by 80 to 400 km. T-RFLP profiles revealed significant differences in bacterial community structure among sponge hosts and ambient bacterioplankton. Pairwise statistical comparisons of clone libraries confirmed the specificity of the bacterial assemblages to each host species and differentiated symbiont communities between color morphs of I. felix. Overall, differences in bacterial communities within each host species and morph were unrelated to location. Our results show a high degree of symbiont fidelity to host sponge across a spatial scale of up to 400 km, suggesting that host-specific rather than biogeographic factors play a primary role in structuring and maintaining sponge–bacteria relationships in Ircinia species from the Bahamas.     

Estimation of carbon biomass and community structure of planktonic bacteria in Lake Biwa using respiratory quinone analysis

The relationship between bacterial respiratory quinone (RQ) concentration and biomass was assessed for Lake Biwa bacterial assemblages to evaluate the utility of bacterial RQ concentration as an indicator of bacterial carbon. The biomass estimated from the RQ concentration correlated well with that from cell volume, indicating that RQ concentration is an appropriate indicator of bacterial biomass. The estimated carbon content per unit of RQ (carbon conversion factor) of bacteria was 0.67 mg C nmol RQ^?1. Bacterial carbon biomass, which was estimated from the RQ concentration using the conversion factor, ranged between 0.008 and 0.054 mg C L^?1 (average 0.025 mg C L^?1) at 5 m depth and between 0.010 and 0.024 mg C L^?1 (average 0.015 mg C L^?1) at 70 m depth. Ubiquinone-8-containing bacteria dominated the epilimnion and hypolimnion. Compared to conventional image analysis, bacterial RQ analysis is a less laborious method of simultaneously determining bacterial biomass and community.     

Spatiotemporal Variation of Bacterial Assemblages in a Shallow Subtropical Coastal Lagoon in Southern Brazil

A study on the bacterioplankton of Conceição Lagoon (27°34′ S–48°27′ W), Southern Brazil, was carried out in July 2005 (austral winter) and January 2006 (austral summer) to characterize the bacterial spatiotemporal distribution and to determine the heterotrophic and photoautotrophic bacterial dominance in hypoxic/oxic stratified waters. Bacterial abundance increased significantly (p?5 (winter) to 3.21?×?10⁶ cells mL^?1 (summer), heterotrophic coccus/rod-shaped (HCR) cells from 7.00?×?10⁴ to 3.60?×?10⁶ cells mL^?1, and heterotrophic filamentous (HF) bacteria from 2.90?×?10³ to 2.74?×?10⁵ cells mL^?1. Bacterial biovolumes also increased in summer with mean biovolumes of CCY ranging from 0.38 to 1.37 μm³, HCR cells from 0.31 to 1.12 μm³, and HF from 3.32 to 11.34 μm³. Principal component analysis showed that salinity, temperature, and light were the abiotic factors that better explained the temporal variability of bacterial assemblages. Bacterial heterotrophy dominated in the lagoon, excepted by the southern and part of central sector in January 2006, when autotrophic-dominated microbial community occurred. Spatially, bacterial assemblages were influenced by nutrient gradient, oxygen, and salinity with a positive relationship between biovolumes and nutrients and a negative relationship between abundance of coccus cyanobacteria and nutrients. area revealed a singular temporal pattern with hypoxic bottom waters in winter and oxygen-rich waters appearing in summer related with the availability of light and predominant microbes. Thus, oxygen consumption/production is likely to be regulated by the amount of light reaching the bottom, stimulating the production of oxygen by oxygenic phototrophs.     

Drastic changes in aquatic bacterial populations from the Cuatro Cienegas Basin (Mexico) in response to long-term environmental stress

Understanding the changes of aquatic microbial community composition in response to changes in temperature and ultraviolet irradiation is relevant for predicting biogeochemical modifications in the functioning of natural microbial communities under global climate change scenarios. Herein we investigate shifts in the bacterioplankton composition in response to long-term changes in temperature and UV radiation. For this purpose, 15 mesocosms were seeded with composite aquatic microbial communities from natural pools within the Cuatro Cienegas Basin (Mexican Chihuahuan desert) and were subject to different temperatures and UV conditions. 16S rRNA gene clone libraries were obtained from water samples at the mid-point (4 months) and the end of the experiment (8 months). An increase in bacterial diversity over time was found in the treatment of constant temperature and UV protection, which suggests that stable environments promote the establishment of complex and diverse bacterial community. Drastic changes in the phylogenetic bacterioplankton composition and structure were observed in response to fluctuating temperature and increasing UV radiation and temperature. Fluctuating temperature induced the largest decrease of bacterial richness during the experiment, indicating that frequent temperature changes drive the reduction in abundance of several species, most notably autotrophs. The long-term impact of these environmental stresses reduced diversity and selected for generalist aquatic bacterial populations, such as Porphyrobacter. These changes at the community level occur at an ecological time scale, suggesting that under global warming scenarios cascade effects on the food web are possible if the microbial diversity is modified.     

Bacterial Growth Efficiency in the Tropical Estuarine and Coastal Waters of Goa,Southwest Coast of India

Bacterial growth efficiency (BGE) is an index of organic carbon passing through bacteria in an aquatic system. BGE values of natural bacterioplankton assemblages were measured in tropical estuarine and adjacent coastal waters in Goa along the southwest coast of India. The BGE values for estuarine and coastal waters were 18 (±7.84%) and 11 (±4.19%), respectively. BGE in these waters were at the lower end of what is usually found in productive systems. This may be due to the high respiration rates. Further, it was observed that grazers also influenced BGE. As BGE was positively correlated with bacterial productivity, the observed variation in BGE was attributed to bacterial productivity. BGE was inversely related to C:N ratio, indicating a close coupling between the nature of the substrates and BGE. Being system-dependent, the variations in BGE at the two locations were dynamic and were regulated by the quality of the substrates. Therefore, a constant value for BGE would lead to error in carbon budgets in these waters.     

Complexity of Bacterial Communities in a River-Floodplain System (Danube, Austria)

Natural floodplains play an essential role in the processing and decomposition of organic matter and in the self-purification ability of rivers, largely due to the activity of bacteria. Knowledge about the composition of bacterial communities and its impact on organic-matter cycling is crucial for the understanding of ecological processes in river-floodplain systems. Particle-associated and free-living bacterial assemblages from the Danube River and various floodplain pools with different hydrological characteristics were investigated using terminal restriction fragment length polymorphism analysis. The particle-associated bacterial community exhibited a higher number of operational taxonomic units (OTUs) and was more heterogeneous in time and space than the free-living community. The temporal dynamics of the community structure were generally higher in isolated floodplain pools. The community structures of the river and the various floodplain pools, as well as those of the particle-associated and free-living bacteria, differed significantly. The compositional dynamics of the planktonic bacterial communities were related to changes in the algal biomass, temperature, and concentrations of organic and inorganic nutrients. The OTU richness of the free-living community was correlated with the concentration and origin of organic matter and the concentration of inorganic nutrients, while no correlation with the OTU richness of the particle-associated assemblage was found. Our results demonstrate the importance of the river-floodplain interactions and the influence of damming and regulation on the bacterial-community composition.     

Complexity of bacterial communities in a river-floodplain system (Danube, Austria)

Natural floodplains play an essential role in the processing and decomposition of organic matter and in the self-purification ability of rivers, largely due to the activity of bacteria. Knowledge about the composition of bacterial communities and its impact on organic-matter cycling is crucial for the understanding of ecological processes in river-floodplain systems. Particle-associated and free-living bacterial assemblages from the Danube River and various floodplain pools with different hydrological characteristics were investigated using terminal restriction fragment length polymorphism analysis. The particle-associated bacterial community exhibited a higher number of operational taxonomic units (OTUs) and was more heterogeneous in time and space than the free-living community. The temporal dynamics of the community structure were generally higher in isolated floodplain pools. The community structures of the river and the various floodplain pools, as well as those of the particle-associated and free-living bacteria, differed significantly. The compositional dynamics of the planktonic bacterial communities were related to changes in the algal biomass, temperature, and concentrations of organic and inorganic nutrients. The OTU richness of the free-living community was correlated with the concentration and origin of organic matter and the concentration of inorganic nutrients, while no correlation with the OTU richness of the particle-associated assemblage was found. Our results demonstrate the importance of the river-floodplain interactions and the influence of damming and regulation on the bacterial-community composition.     

Seasonal and Spatial Variability of Bacterial and Archaeal Assemblages in the Coastal Waters near Anvers Island, Antarctica

A previous report of high levels of members of the domain Archaea in Antarctic coastal waters prompted us to investigate the ecology of Antarctic planktonic prokaryotes. rRNA hybridization techniques and denaturing gradient gel electrophoresis (DGGE) analysis of the bacterial V3 region were used to study variation in Antarctic picoplankton assemblages. In Anvers Island nearshore waters during late winter to early spring, the amounts of archaeal rRNA ranged from 17.1 to 3.6% of the total picoplankton rRNA in 1996 and from 16.0 to 1.0% of the total rRNA in 1995. Offshore in the Palmer Basin, the levels of archaeal rRNA throughout the water column were higher (average, 24% of the total rRNA) during the same period in 1996. The archaeal rRNA levels in nearshore waters followed a highly seasonal pattern and markedly decreased during the austral summer at two stations. There was a significant negative correlation between archaeal rRNA levels and phytoplankton levels (as inferred from chlorophyll a concentrations) in nearshore surface waters during the early spring of 1995 and during an 8-month period in 1996 and 1997. In situ hybridization experiments revealed that 5 to 14% of DAPI (4′,6-diamidino-2-phenylindole)-stained cells were archaeal, corresponding to 0.9 × 10⁴ to 2.7 × 10⁴ archaeal cells per ml, in late winter 1996 samples. Analysis of bacterial ribosomal DNA fragments by DGGE revealed that the assemblage composition may reflect changes in water column stability, depth, or season. The data indicate that changes in Antarctic seasons are accompanied by significant shifts in the species composition of bacterioplankton assemblages and by large decreases in the relative proportion of archaeal rRNA in the nearshore water column.     

Distribution of viruses in the water column of the ice-covered Rybinsk Reservoir and their contribution to heterotrophic bacteria mortality

Virioplankton and bacterioplankton abundance has been determined in the pelagic and littoral zones of the Rybinsk Reservoir during the ice-covered period. The role of viruses in heterotrophic bacterioplankton infection and mortality is assessed. At water temperatures between 0.3 and 0.9°C, the number of planktonic virus particles and planktonic bacteria varies from 37.1 × 10⁶ to 84.1 × 10⁶ particles/mL, (57.3 ± 2.1) × 10⁶ particles/mL on average and from 2.50 × 10⁶ to 6.11 × 10⁶ cells/mL, (3.66 ± 0.16) × 10⁶ cells/mL on average, respectively. The ratio of the virus number to the bacteria number varies from 8.8 to 27.9, being 16.5 ± 0.7 on average. Visually infected cells comprise 0.3–0.5% (1.5 ± 0.2% on average) of the total number of bacterioplankton. Infected bacterial cells contain from 5 to 107 (17 ± 4 on average) mature virus particles. The average virus-induced mortality of bacteria accounts for 13.0 ± 1.9% (variations range from 2 to 55%) of the daily bacterial production, indicating that viruses play an important role in the regulation of bacterioplankton production and abundance in the Rybinsk Reservoir during the ice-covered period.     

虾池生态系各有机碳库的储量

1997年6～8月于山东省海阳市黄海集团公司养虾场,采用围隔实验生态学方法研究了虾池生态系各有机碳库的储量,结果表明:溶解有机碳(DOC)、颗粒有机碳(POC)库储量(mgC/l)平均分别为9.95±2.04及3.10±1.60,DOC/POC比值平均为3.21.POC库中,腐质颗粒碳为总浮游生物碳的2倍.浮游植物碳、浮游动物碳、浮游细菌碳平均分别占总浮游生物碳的53%、13%及34%.腐质碳、总浮游生物碳平均分别占总有机碳(TOC)的92%及8%,腐质碳为总浮游生物碳的11.08倍.     

Protistan grazing and viral lysis losses of bacterial carbon production in a large mesotrophic lake (Lake Biwa)

The grazing and lysis mortalities of planktonic bacteria were estimated using the modified dilution method and respiratory quinone (RQ) analysis in mesotrophic Lake Biwa, Japan. The planktonic bacterial assemblages in the lake consisted of various RQ subgroups with different growth and mortality rates. The sum of total bacterial mortalities due to protistan grazing and viral lysis accounted for 96.6 % (range 89.0–107.2 %) of daily total bacterial production. This is the first report that successfully demonstrates a balanced relationship between bacterial production and losses using the modified dilution method in a lake. The growth rates of ubiquinone (UQ)-containing bacteria were faster than those of menaquinone-containing bacteria. Especially the dominant and fastest growing bacterial groups in the present study were the bacterial groups containing UQ-8 or UQ-10. The sum of their production and loss accounted for 60 % of carbon fluxes within the microbial loop. Thus, a large portion of the carbon cycling through the bacterial community in Lake Biwa can be explained by the carbon fluxes through dominant bacterial groups.     

Solar UV radiation modulates daily production and DNA damage of marine bacterioplankton from a productive upwelling zone (36°S), Chile

In upwelling ecosystems, such as the Humboldt Current system (HCS) off Concepción, the effects of solar radiation on bacterioplankton incorporation rates have been related to previous light acclimation and responses to irradiance. In this paper, we study the daily effect of Photosynthetic Active Radiation (PAR, 400-700 nm) and ultraviolet radiation UVR (280-400 nm) on bacterial secondary production (BSP). We also considered the DNA damage-repair response to solar radiation stress by the induction of cyclobutane pyrimidine dimers (CPDs). Experiments were conducted with natural bacterioplankton assemblages (0.2-0.7 μm) collected off Concepción (36°S), during the austral Spring, October-November, 2004. Surface (0.5 m) and subsurface (80 m) bacterioplankton samples were exposed to different solar radiation treatments for 5-20 h. BSP was estimated by ¹⁴C-leucine and ³H-thymidine incorporation at several time intervals, whereas CPDs accumulation was assessed using immunoassay techniques. During high irradiance periods, BSP was mainly affected by PAR in both surface and subsurface assemblages and, to a lesser, but significant (Tukey < 0.05) extent, by UV-A (320-400 nm) and UV-B (280-320 nm) radiation. Maximum inhibition of BSP in surface waters was 78%; growth rates (μ) and bacterial growth efficiency (BGE) were also low (78% and 66% respectively). Subsurface water assemblages, on the contrary, showed a ∼ 25 fold enhancement of BSP, μ, and BGE. Both types of assemblages had a rapid CPDs accumulation (maximum 60 CPDs Mb^− 1) during high irradiance periods. Recovery of BSP inhibition and DNA damage in surface bacteria was total after sunset and after the night incubation period, resembling pre-exposure levels. Despite subsurface BSP enhancement during day-night exposure, residual DNA damage was detected at the end of the experiment (20 CPDs Mb^− 1) suggesting a chronic DNA damage. Our results represent the worst case scenario (i.e., assemblages receiving surface irradiances as may occur in this upwelling zone) and indicate that surface and subsurface bacterial assemblages in the HCS are both highly sensitive to solar irradiance. However, they showed different responses, with surface bacteria having more effective photorepair mechanisms, and sustaining higher BSP than subsurface assemblages.     

Phylogenetic composition of bacterial communities in small boreal lakes and ombrotrophic bogs of the upper Volga basin

Fluorescent in situ hybridization (FISH) with rRNA-specific oligonucleotide probes was used to assess the numbers and phylogenetic diversity of prokaryotic microorganisms in the water of small boreal lakes and peatland catchments of the swampy upper Volga basin. The abundance of bacterioplankton in lake water was found to vary from 1.6 to 8.7 × 10⁶ cells ml⁻¹, with the highest values detected in neutral eutrophic lakes. The total cell numbers in the peat of ombrotrophic bogs were 3.9–4.3 × 10⁸ cells g⁻¹ of wet peat. The proportion of bacteria identified by the group-specific probes decreased from 79–85% in neutral (pH 6.6–6.9) mesotrophic and eutrophic lakes to 65–69% in acidic (pH 4.4–5.5) dystrophic lakes and to 51–58% in the peat of acidic (pH 3.6–3.9) ombrotrophic bogs. The diversity of bacterial communities was highest in lakes with neutral water. These communities were dominated by members of the phylum Actinobacteria (31–44% of the total bacterial number), while the contribution of Alphaproteobacteria (16–19%), Bacteroidetes (6–16%), Betaproteobacteria (6–7%), Planctomycetes (2–8%), and Gammaproteobacteria (4–5%) was also significant. In acidic dystrophic lakes, Actinobacteria (25–35%) and Betaproteobacteria (25–34%) predominated, while peatland catchments were dominated by the Alphaproteobacteria (20–23%). The presence of acidobacteria and some planctomycetes common for bogs in the water of acidic dystrophic lakes, as well as the high proportion of bacteria (31–49%) that were not identified by the group-specific probes, suggest the impact of microbial processes in peatland catchments on the microbial composition of the receiving waters.     

Between-site comparison of freshwater bacterioplankton by DNA hybridization

Natural assemblages of freshwater bacterioplankton in enriched lowland rivers had greater cell-specific metabolic activity than those in gravel-pit ponds. Similarly, cell-specific activity and mean cell Size in calcareous headstreams tended to be greater than in intermittently-acid headstreams on millstone grit. DNA was extracted and purified from bacterioplankton assemblages, and between-site comparisons were made in terms of percentage similarity as indicated by DNA hybridization. Cluster analysis, using percentage-similarity matrices, placed bacterioplankton assemblages from different site types into distinct groups. This suggested that between-site physiological differences were related to intrinsically different bacterial composition rather than to different physiological response to different environmental conditions by essentially similar bacterial assemblages. Offprint requests to: R. Goulder.     

Bacterial Growth Efficiency in a Tropical Estuary: Seasonal Variability Subsidized by Allochthonous Carbon

Bacterial growth efficiency (BGE) is a key factor in understanding bacterial influence on carbon flow in aquatic ecosystems. We report intra-annual variability in BGE, and bacteria-mediated carbon flow in the tropical Mandovi and Zuari estuaries (southwest India) and the adjoining coastal waters (Arabian Sea). BGE ranged from 3% to 61% and showed clear temporal variability with significantly (ANOVA, p < 0.01) higher values in the estuaries (mean, 28 ± 14%) than coastal waters (mean, 12 ± 6%). The greater variability of BGE in the estuaries than coastal waters suggest some systematic response to nutrient composition and the variability of dissolved organic matter pools, as BGE was governed by bacterial secondary production (BP). Monsoonal rains and its accompanied changes brought significant variability in BGE and bacterial productivity/primary productivity (BP/PP) ratio when compared to nonmonsoon seasons in the estuaries and coastal waters. High BP/PP ratio (>1) together with high carbon flux through bacteria (>100% of primary productivity) in the estuarine and coastal waters suggests that bacterioplankton consumed dissolved organic carbon in excess of the amount produced in situ by phytoplankton of this region, which led to the mismatch between primary production of carbon and amount of carbon consumed by bacteria. Despite the two systems being subsidized by allochthonous inputs, the low BGE in the coastal waters may be attributable to the nature and time interval in the supply of allochthonous carbon.     

Large Plankton Enhance Heterotrophy Under Experimental Warming in a Temperate Coastal Ecosystem

Microbes are key players in oceanic carbon fluxes. Temperate ecosystems are seasonally variable and thus suitable for testing the effect of warming on microbial carbon fluxes at contrasting oceanographic conditions. In four experiments conducted in February, April, August and October 2013 in coastal NE Atlantic waters, we monitored microbial plankton stocks and daily rates of primary production, bacterial heterotrophic production and respiration at in situ temperature and at 2 and 4°C over ambient values during 4-day incubations. Ambient total primary production (TPP) exceeded total community respiration (< 200 µm, TR) in winter and fall but not in spring and summer. The bacterial contribution to ecosystem carbon fluxes was low, with bacterial production representing on average 6.9 ± 3.2% of TPP and bacterial respiration (between 0.8 and 0.2 µm) contributing on average 35 ± 7% to TR. Warming did not result in a uniform increase in the variables considered, and most significant effects were found only for the 4°C increase. In the summer and fall experiments, under warm and nutrient-deficient conditions, the net TPP/TR ratio decreased by 39 and 34% in the 4°C treatment, mainly due to the increase in respiration of large organisms rather than bacteria. Our results indicate that the interaction of temperature and substrate availability in determining microbial carbon fluxes has a strong seasonal component in temperate planktonic ecosystems, with temperature having a more pronounced effect and generating a shift toward net heterotrophy under more oligotrophic conditions as found in summer and early fall.     

Virus impact on heterotrophic bacterioplankton of water reservoirs

The quantitative distribution of viruses and their impact on heterotrophic bacterioplankton were studied in mesotrophic and eutrophic reservoirs of the Volga and Volga-Baltic waterway. The abundance of planktonic virus particles ranged from 9.4 × 10⁶ to 120 × 10⁶ ml⁻¹ and was from 2.5 to 9 times greater than the bacterial numbers. Production of virioplankton varied from 2.1 × 10⁶ to 132 × 10⁶ particles (ml day)⁻¹ and the population turnover time values were between 0.3 and 11.6 days. The maximum values of numbers and production of virio- and bacterioplankton were observed in the eutrophic Ivan’kovo reservoir. Distribution of the viruses in the Volga reservoirs depended to a significant degree on the number and activity of heterotrophic bacterioplankton. The infected bacteria accounted for 5.5–33.5% of the total bacterial abundance. Phages were an important factor of bacterial mortality. During July to September virus-induced bacterial mortality varied between 6.1 and 40.6% (20.2% on average) of daily bacterioplankton production.     

Abundance and community composition of bacterioplankton in the Northern South China Sea during winter: geographic position and water layer influences

The abundance and composition of bacterioplankton of the Northern South China Sea (NSCS) were investigated using flow cytometry and high-throughput sequencing. The results showed that the absolute abundance of bacterioplankton retained high values in surface waters at both continental shelf and oceanic sites and Proteobacteria, Cyanobacteria, and Bacteroidetes represented the three typical dominant phyla in NSCS. The average bacterioplankton abundances at 5 m, 75 m, and 200 m were 9.55, 5.04, and 1.32?×?10⁵ cells mL^?1, respectively, and there was a significantly positive correlation between bacterioplankton abundance and Chl a content (r?=?0.84, p?<?0.01). Drastic changes of the bacterioplankton community occurred in different water layers. Three operational taxonomic units (OTUs), whose distribution were significantly different between 5-m and 75-m water layers, all belonged to Flavobacteriales of the Bacteroidetes (p?<?0.05). In addition, bacterioplankton community richness and diversity at the continental shelf (CS) was generally higher than at oceanic stations (SB and KI). Five OTUs, which favored the habitat of continental shelf, belonged to Alphaproteobacteria including the orders of the SAR11 cluster, Rhodospirillales, Rhodobacterales and other unclassified orders (p?<?0.05). Two OTUs, which favored the habitat of oceanic stations, were assigned to the orders of Flavobacteriales and Alteromonadales. Furthermore, the abundances of two OTUs belonging to the Cyanobacteria phylum and Verrucomicrobiales order were significantly different between the sea basin (SB) and Kuroshio influenced area (KI) stations (p?<?0.05).     

Distribution of marine viruses and their potential hosts in Prydz Bay and adjacent Southern Ocean,Antarctic

Viruses play a key role in all marine ecosystems, and yet little is known of their distribution in Antarctic waters, especially in bathypelagic waters (>1000 m). In this study, the abundance and distribution of viruses and their potential hosts from the surface to the bottom of Prydz Bay, Antarctic, was investigated using flow cytometry. Viruses and autotrophs were abundant in nearshore and continental shelf waters, while heterotrophic bacteria and picoeukaryotes were abundant in offshore waters. Virus and bacteria abundances generally decreased with increasing depth but increased slightly just above the seafloor. Within the water column, maximum virus numbers coincided with the maximum values of chlorophyll a (when greater than 0.1 μg l^?1), in the surface and subsurface (25 m). In the open ocean, however, virus abundance usually correlated with bacterial abundance at greater depths (50, 300 and 500 m) where the surface chlorophyll a concentration was lower than 0.1 μg l^?1. Viral abundance was correlated with the host cell abundance, and this was different in different pelagic zones (bacteria and autotrophs (i.e., chlorophyll a concentration) in the epipelagic waters, picoeukaryotes and bacteria in mesopelagic waters and bacteria in bathypelagic waters). Principle component analysis and Pearson correlation analysis indicated that there was a close relationship between virus abundance and chlorophyll a, bacteria and nutrients (NO₂ + NO₃, phosphate and silicate), and picoeukaryote abundance was mainly correlated with water depth and salinity.