Summary
In aquatic ecosystems, microplastics are a relatively new anthropogenic substrate that can readily be colonized by biofilm‐forming organisms. To examine the effects of substrate type on ...microbial community assembly, we exposed ambient Baltic bacterioplankton to plastic substrates commonly found in marine environments (polyethylene, polypropylene and polystyrene) as well as native (cellulose) and inert (glass beads) particles for 2 weeks under controlled conditions. The source microbial communities and those of the biofilms were analyzed by Illumina sequencing of the 16S rRNA gene libraries. All biofilm communities displayed lower diversity and evenness compared with the source community, suggesting substrate‐driven selection. Moreover, the plastics‐associated communities were distinctly different from those on the non‐plastic substrates. Whereas plastics hosted greater than twofold higher abundance of Burkholderiales, the non‐plastic substrates had a significantly higher proportion of Actinobacteria and Cytophagia. Variation in the community structure, but not the cell abundance, across the treatments was strongly linked to the substrate hydrophobicity. Thus, microplastics host distinct bacterial communities, at least during early successional stages.
The vertical distribution of phytoplankton is of fundamental importance in the structure, dynamic, and biogeochemical pathways in marine ecosystems. Nevertheless, what are the main factors ...determining this distribution remains as an open question. Here, we evaluated the relative influence of environmental factors that might control the coexistence and vertical distribution of pico-nanoplankton associated with the OMZ off northern Chile. Our results showed that in the upper layer Synechococcus-like cells were numerically important at all sampling stations. Pico-nano eukaryotes and phototrophic nanoflagellates (PNF) also showed high abundances in the upper layer decreasing in abundance down to the upper oxycline, while only Prochlorococcus showed high abundances under oxycline and within the oxygen-depleted layer. Statistical analyses evidenced that temperature, oxygen, and carbonate chemistry parameters (pH and dissolved inorganic carbon, DIC) influenced significantly the vertical distribution of phototrophic pico-nanoplankton. Additionally, we experimentally-evaluated the combined effect of low pH/low O2 conditions on a nanophytoplankton species, the haptophyte Imantonia sp. Under control conditions (pH = 8.1; O2 = 287.5 μM, light = 169.6 μEm−2s−1), Imantonia sp. in vivo fluorescence increased over fifty times, inducing supersaturated O2 conditions (900 μM) and an increasing pH (8.5), whereas upon an experimental treatment mimicking OMZ conditions (pH = 7.5; O2 = 55.6 μM; light = 169.6 μEm−2s−1), in vivo fluorescence declined dramatically, suggesting that Imantonia sp. did not survive. Although preliminary, our study provides evidence about the role of low pH/low O2 conditions on the vertical distribution of nanophytoplankton, which deserve future attention through both fieldwork and more extended experimental experiences.
•Pico-nano eukaryotes and phototrophic nanoflagellates showed high abundances in the upper layer decreasing in abundance down to the upper oxycline.•Temperature, oxygen, and carbonate chemistry parameters (pH and dissolved inorganic carbon, DIC) influenced significantly the vertical distribution of phototrophic pico-nanoplankton.•The phototrophic nanoflagellate Imantonia sp. upon an experimental treatment mimicking OMZ conditions, declined dramatically, suggesting this nanoflagellate did not survive upon such conditions.
The study assessed the Cochin estuary and adjacent coastal Arabian Sea for their seasonal variation in nitrate (NO3−) and ammonium (NH4+) uptake rates by total and nano + picoplankton using the 15N ...tracer technique. The results suggested that the NO3− and NH4+ uptake rates in the Cochin estuary are higher than those in the adjacent coastal Arabian Sea. NO3− and NH4+ uptake rates in the nearshore stations in the off Cochin station were high, indicating the influence of the eutrophic estuary. NO3− and NH4+ uptake rates conducted in off Mangalore transect were significantly lower than those of the off Cochin as it does not have an exchange with eutrophic systems. The nano + picoplankton's contribution to the total DIN uptake rates in the Cochin estuary was 77–98 %, indicating the relevance of nano + pico phytoplankton in the N cycling of the region.
•Nano + pico phytoplankton contributes up to 77-98 % of the total DIN uptake rate in the Cochin estuary.•Evidence of the influence of eutrophication in the estuary of DIN uptake rates in the coastal Arabian Sea.•DIN uptake potential of phytoplankton depends on TN:TP ratio rather than the individual nutrient concentrations.
Summary
Primers targeting the 16S small subunit ribosomal RNA marker gene, used to characterize bacterial and archaeal communities, have recently been re‐evaluated for marine planktonic habitats. To ...investigate whether primer selection affects the ecological interpretation of bacterioplankton populations and community dynamics, amplicon sequencing with four primer sets targeting several hypervariable regions of the 16S rRNA gene was conducted on both mock communities constructed from cloned 16S rRNA genes and a time‐series of DNA samples from the temperate coastal Santa Barbara Channel. Ecological interpretations of community structure (delineation of depth and seasonality, correlations with environmental factors) were similar across primer sets, while population dynamics varied. We observed substantial differences in relative abundances of taxa known to be poorly resolved by some primer sets, such as Thaumarchaeota and SAR11, and unexpected taxa including Roseobacter clades. Though the magnitude of relative abundances of common OTUs differed between primer sets, the relative abundances of the OTUs were nonetheless strongly correlated. We do not endorse one primer set but rather enumerate strengths and weaknesses to facilitate selection appropriate to a system or experimental goal. While 16S rRNA gene primer bias suggests caution in assessing quantitative population dynamics, community dynamics appear robust across studies using different primers.
In November 2019, a first joint Chilean–Argentinian research cruise was conducted along the eastern section of the Beagle Channel (BC). Here we present the results of the microbial plankton (2–200 μm ...cell size) abundance and composition analyses in relation to water masses and environmental variables, along a longitudinal transect characterized by contrasting hydrology. Plankton samples were analyzed within the photic zone along the channel and at two fixed stations during two short time series (a first one of 30 and a second one of 42 h). Results revealed a spatial zonation in the composition and structure of the plankton assemblages, related to bathymetry, water temperature and nutrient availability but also, a small-scale temporal variability due mainly to a rise in air and water temperature. The inner (westernmost) and outer sectors of the sampled area, west and east of Mackinlay Strait, respectively, were characterized by low plankton abundances, mostly dominated by nanoflagellates and some large diatoms. In contrast, the easternmost sector of BC, showed the highest total cell abundances, displaying a high diversity of small and large diatoms. Notably, in the inner BC (fixed station F1), chlorophyll-a (chl-a) concentrations almost doubled in 24 h, along with an increase in total plankton abundance and the dominance of small diatoms and nanoflagellates. Rapid changes in plankton relative abundance were also observed east to Mackinlay Strait. This highlights the large spatial (km) and temporal (hours to days) plankton heterogeneity along the eastern section of the BC, scales which should be considered for further sampling strategies.
•Spatial variability in microphytoplankton was observed along the Beagle Channel (BC).•Phytoplankton assemblages were related to bathymetry, temperature, and macronutrients.•Fast changes in plankton were related to growth rather than advection of water masses.•Temperature and wind speed affected both chl-a concentration and phytoplankton growth.•This is the first work to report such high temporal variability in plankton in the BC.
Dendritic stream networks are an intriguing subject for exploring the spatial and temporal variability of the rare and common bacterial biosphere, yet very few such studies have been conducted. We ...sampled riverine bacterioplankton at 13 sites in a subarctic riverine network across 3 years, with five sampling times each year. Ordinations showed a consistent pattern of downstream shift for both rare and abundant subcommunities. We also detected a temporal signal, with seasonal community shifts reflecting changes in water temperature and groundwater contribution, and an inter‐annual pattern where the year 2018 differed from other years. Phylogenetic turnover of the rare subcommunity indicated homogeneous selection, whereas the abundant subcommunity was mainly stochastically structured. Transiently rare taxa were the dominant type of rarity with the highest proportion at the headwater regions. The bacterioplankton community was characterized by a small group of core taxa that occurred at most sites with little temporal variation, a very large number of permanently or transiently rare taxa, and taxa shifting through time between the rare and abundant biosphere. While this basic structure could have been detected with less extensive temporal replication, a comprehensive understanding of the rare biosphere in riverine bacterioplankton can only be achieved via inter‐annual, spatially replicated sampling that covers the whole stream network.
The high bacterial diversity in headwaters is caused mainly by the rare taxa. Conditional taxa, however, contribute most to temporal community variability of stream bacterioplankton.
Summary
Microbial communities in natural ecosystems are subject to strong ecological rules. The study of local communities along a regional metacommunity can reveal patterns of community assembly, ...and disentangle the underlying ecological processes. In particular, we seek drivers of community assembly at the regional scale using a large lacustrine dataset (>300 lakes) along the geographical, limnological and physico‐chemical gradients in the Pyrenees. By using high throughput amplicon sequencing of the 16S rRNA gene, and inferring environmental sources of bacterial immigrants, we showed that surface aquatic bacterial assemblages were strongly influenced by terrestrial populations from soil, biofilms or sediments, and primarily selected by a pH‐alkalinity gradient. Indeed, source proportions explained 27% of the community variation, and chemistry 15% of the total variation, half of it shared with the sources. Major taxonomic groups such as Verrucomicrobia, Actinobacteria and Bacteroidetes showed higher aquatic affinities than Parcubacteria, Gammaproteobacteria, Alphaproteobacteria or Betaproteobacteria, which may be recruited and selected through different hydrographic habitats. A regional fingerprint was observed with lower alpha diversity and higher beta diversity in the central Pyrenees than in both ends. We suggest an ecological succession process, likely influenced by complex interactions of environmental source dispersal and environmental filtering along the mountain range geography.
The present study aims to explore the bioaccumulation and biotic transformations of inorganic (iHg) and monomethyl mercury (MMHg) by natural pico-nanoplankton community from eutrophic lake Soppen, ...Switzerland. Pico-nanoplankton encompass mainly bacterioplankton, mycoplankton and phytoplankton groups with size between 0.2 and 20 μm. Species-specific enriched isotope mixture of 199iHg and 201MMHg was used to explore the accumulation, the subcellular distribution and transformations occurring in natural pico-nanoplankton sampled at 2 different depths (6.6 m and 8.3 m). Cyanobacteria, diatoms, cryptophyta, green algae and heterotrophic microorganisms were identified as the major groups of pico-nanoplankton with diatoms prevailing at deeper samples. Results showed that pico-nanoplankton accumulated both iHg and MMHg preferentially in the cell membrane/organelles, despite observed losses. The ratios between the iHg and MMHg concentrations measured in the membrane/organelles and cytosol were comparable for iHg and MMHg. Pico-nanoplankton demethylate added 201MMHg (~4 and 12% per day depending on cellular compartment), although the involved pathways are to further explore. Comparison of the concentrations of 201iHg formed from 201MMHg demethylation in whole system, medium and whole cells showed that 82% of the demethylation was biologically mediated by pico-nanoplankton. No significant methylation of iHg by pico-nanoplankton was observed. The accumulation of iHg and MMHg and the percentage of demethylated MMHg correlated positively with the relative abundance of diatoms and heterotrophic microorganisms in the pico-nanoplankton, the concentrations of TN, Mg2+, NO3−, NO2−, NH4+ and negatively with the concentrations of DOC, K+, Na+, Ca2+, SO42−. Taken together the results of the present field study confirm the role of pico-nanoplankton in Hg bioaccumulation and demethylation, however further research is needed to better understand the underlying mechanisms and interconnection between heterotrophic and autotrophic microorganisms.
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•Pico-nanoplankton encompass bacterio-, myco- and phytoplankton with size 0.2–20 μm.•Natural pico-nanoplankton from eutrophic lake accumulate iHg and MMHg.•IHg and MMHg preferentially accumulate in the cell membrane/organelles.•Pico-nanoplankton demethylate MMHg, although the pathways are to further explore.•Demethylation positively correlated with the abundance of diatoms and heterotrophs.
Heterotrophy in Tropical Scleractinian Corals Houlbreque, Fanny; Ferrier-Pages, Christine
Biological reviews of the Cambridge Philosophical Society,
February 2009, Letnik:
84, Številka:
1
Journal Article
Recenzirano
The dual character of corals, that they are both auto‐ and heterotrophs, was recognized early in the twentieth Century. It is generally accepted that the symbiotic association between corals and ...their endosymbiotic algae (called zooxanthellae) is fundamental to the development of coral reefs in oligotrophic tropical oceans because zooxanthellae transfer the major part of their photosynthates to the coral host (autotrophic nutrition). However, numerous studies have confirmed that many species of corals are also active heterotrophs, ingesting organisms ranging from bacteria to mesozooplankton. Heterotrophy accounts for between 0 and 66% of the fixed carbon incorporated into coral skeletons and can meet from 15 to 35% of daily metabolic requirements in healthy corals and up to 100% in bleached corals. Apart from this carbon input, feeding is likely to be important to most scleractinian corals, since nitrogen, phosphorus, and other nutrients that cannot be supplied from photosynthesis by the coral’s symbiotic algae must come from zooplankton capture, particulate matter or dissolved compounds. A recent study showed that during bleaching events some coral species, by increasing their feeding rates, are able to maintain and restore energy reserves.
This review assesses the importance and effects of heterotrophy in tropical scleractinian corals. We first provide background information on the different food sources (from dissolved organic matter to meso‐ and macrozooplankton). We then consider the nutritional inputs of feeding. Finally, we review feeding effects on the different physiological parameters of corals (tissue composition, photosynthesis and skeletal growth).
During a cruise from October to November 2019, along the West Antarctic Peninsula, between 64.32 and 68.37°S, we assessed the diversity and composition of the active microbial eukaryotic community ...within three size fractions: micro- (> 20 μm), nano- (20-5 μm), and pico-size fractions (5-0.2 μm). The communities and the environmental parameters displayed latitudinal gradients, and we observed a strong similarity in the microbial eukaryotic communities as well as the environmental parameters between the sub-surface and the deep chlorophyll maximum (DCM) depths. Chlorophyll concentrations were low, and the mixed layer was shallow for most of the 17 stations sampled. The richness of the microplankton was higher in Marguerite Bay (our southernmost stations), compared to more northern stations, while the diversity for the nano- and pico-plankton was relatively stable across latitude. The microplankton communities were dominated by autotrophs, mostly diatoms, while mixotrophs (phototrophs-consuming bacteria and kleptoplastidic ciliates, mostly alveolates, and cryptophytes) were the most abundant and active members of the nano- and picoplankton communities. While phototrophy was the dominant trophic mode, heterotrophy (mixotrophy, phagotrophy, and parasitism) tended to increase southward. The samples from Marguerite Bay showed a distinct community with a high diversity of nanoplankton predators, including spirotrich ciliates, and dinoflagellates, while cryptophytes were observed elsewhere. Some lineages were significantly related-either positively or negatively-to ice coverage (e.g., positive for Pelagophyceae, negative for Spirotrichea) and temperature (e.g., positive for Cryptophyceae, negative for Spirotrichea). This suggests that climate changes will have a strong impact on the microbial eukaryotic community.
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