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  Subjects -> WATER RESOURCES (Total: 160 journals)
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Journal of Oceanology and Limnology
Journal Prestige (SJR): 0.301
Citation Impact (citeScore): 1
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  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2096-5508 - ISSN (Online) 2523-3521
Published by Springer-Verlag Homepage  [2469 journals]
  • Biofilm formation under high temperature causes the commensal bacteria
           Bacillus cereus WPySW2 to shift from friend to foe in Neoporphyra
           haitanensis in vitro model

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      Abstract: Abstract Although biofilm formation may promote growth, biofilms are not always beneficial to their hosts. The biofilm formation characteristics of Bacillus cereus WPySW2 and its changes at different temperatures were studied. Results show that B. cereus WPySW2 promoted the growth of Neoporphyra haitanensis (an economically cultivated seaweed) at 20 °C but accelerated algal rot at 28 °C. Thicker B. cereus WPySW2 biofilms covered the surface of N. haitanensis thalli at 28 °C, which hindered material exchange between the algae and surrounding environment, inhibited algal photosynthesis and respiration, and accelerated algal decay. Compared with planktonic bacteria, mature biofilm cells had lower energy consumption and metabolic levels. The biofilm metabolic characteristics of B. cereus WPySW2 changed significantly with temperature. High temperature accelerated biofilm maturation, which made it thicker and more stable, allowing the bacteria to easily adapt to environmental changes and obtain greater benefits from their host. High temperature did not affect the production or increased the abundance of toxic metabolites, indicating that the negative effects of B. cereus WPySW2 on algae were not caused by toxins. This study shows that increased temperature can transform a harmless bacterium into a detrimental one, demonstrating that temperature may change the ecological function of phycospheric bacteria by affecting their morphology and metabolism.
      PubDate: 2022-09-20
       
  • Assessment of heavy metal pollution in Laizhou Bay (China) using the
           ecological risk index and the integrated biomarker response of the goby
           Acanthogobius ommaturus

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      Abstract: Abstract We used the Integrated Biological Responses version 2 (IBRv2) method to evaluate the biological effects of heavy metals in the sediments in Laizhou Bay, China on the benthic goby Acanthogobius ommaturus. In December 2018, gobies and sediments were collected from 15 stations. We measured the activities of defense enzymes and the contents of malondialdehyde (MDA) and metallothionein (MT) in the goby liver as well as the levels of heavy metals in the sediments and goby muscle tissue. Most of the heavy metal concentrations in sediment at each station were below the Class I criteria set by Chinese Standards for Marine Sediment Quality, and the Håkanson ecological risk index suggested low risk for the heavy metals. We found that A. ommaturus could effectively accumulate mercury, cadmium, arsenic, and zinc and that the contents of MT and MDA and the activities of glutathione peroxidase and glutathione reductase were suitable biomarkers of heavy metal pollution in this species. The IBRv2 method integrated these four biomarkers and discriminated stations according to heavy metal pollution. Higher IBRv2 values suggested more adverse effects in gobies, corroborating more serious heavy metal contamination. The stations with high IBRv2 values and high contents of heavy metals were mainly distributed in the west and northeast parts of the bay. These results show that the IBRv2 approach is a feasible strategy for assessing heavy metal pollution through biological response and biological status and that it can be implemented for environmental monitoring in Laizhou Bay.
      PubDate: 2022-09-20
       
  • Molecular identification, expression pattern, and in-vitro bioactivity
           analysis of insulin-like growth factor 2 in olive flounder Paralichthys
           olivaceus

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      Abstract: Abstract Insulin-like growth factors (IGFs) are key regulators of development and growth. Here, we characterized the igf2 gene from olive flounder (Paralichthys olivaceus) and determined its temporal and spatial expression. We set up an in-vitro protein expression system in eukaryotic human embryonic kidney (HEK293T) cells and explored its effects on cell proliferation. The flounder igf2 cDNA contained a 648-bp open reading frame (ORF) encoding a protein of 215 amino acids (aa), which spanned the complete signal peptide (47 aa), mature peptide (70 aa), and E domain (98 aa). In adult flounder, igf2 mRNA was detected in all selected tissues. In early development, igf2 mRNA was detected throughout development from unfertilized eggs to hatching-stage embryos. In-situ hybridization analysis indicated that igf2 mRNA was specially expressed in the brain region, floor plate, hypochord, otic vesicle, and pectoral fin during embryogenesis. Western blotting analysis indicated that the soluble recombinant flounder IGF2 protein was successfully produced through eukaryotic expression in HEK293T cells. In addition, the recombinant IGF2 protein significantly promoted the proliferation of human cervical carcinoma (HeLa) and HEK293T cells. These results provide new information about the structural and functional conservation, expression patterns, and biological activity of the igf2 in teleosts.
      PubDate: 2022-09-20
       
  • Structural characterization of sulfated galactofucan from Undaria
           pinnatifida and its effect on type 2 diabetic mice

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      Abstract: Abstract A sulfated galactofucan designated as UpG was obtained from the brown algae Undaria pinnatifida by calcium chloride extraction. Chemical analyses showed that UpG is composed of galactose and fucose at a high sulfation level. Low-molecular weight UpGP-0.5 was prepared from UpG through acid hydrolysis for structure characterization. The backbones of UpG are determined to be α-(1,3)-Fuc, α-(1,4)-Gal, α-(1,3)-Gal, and α-(1,6)-Gal by GC-MS, FT-IR, NMR, and LC-MS analyses. Sulfate groups are modified at C2 and/or C4 of fucose and C3 and/or C4 of galactose. UpG could partially lower blood sugar and serum lipid levels in type 2 diabetic mice. Moreover, UpG treatment regulates the abundance of some specific gut microbiota, such as enriching the abundance of Muribaculum and Christensenellaceae, and reducing that of Bilophila, Tannerellaceae, Candidatus Saccharimonas and Anaerotruncus. The findings characterized the detailed structure of a sulfated galactofucan and investigated its potential for the treatment of type 2 diabetes mellitus.
      PubDate: 2022-09-20
       
  • Identification of paralytic shellfish toxin-producing microalgae using
           machine learning and deep learning methods

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      Abstract: Abstract Paralytic shellfish poisoning (PSP) microalgae, as one of the harmful algal blooms, causes great damage to the offshore fishery, marine culture, and marine ecological environment. At present, there is no technique for real-time accurate identification of toxic microalgae, by combining three-dimensional fluorescence with machine learning (ML) and deep learning (DL), we developed methods to classify the PSP and non-PSP microalgae. The average classification accuracies of these two methods for microalgae are above 90%, and the accuracies for discriminating 12 microalgae species in PSP and non-PSP microalgae are above 94%. When the emission wavelength is 650–690 nm, the fluorescence characteristics bands (excitation wavelength) occur differently at 410–480 nm and 500–560 nm for PSP and non-PSP microalgae, respectively. The identification accuracies of ML models (support vector machine (SVM), and k-nearest neighbor rule (k-NN)), and DL model (convolutional neural network (CNN)) to PSP microalgae are 96.25%, 96.36%, and 95.88% respectively, indicating that ML and DL are suitable for the classification of toxic microalgae.
      PubDate: 2022-09-20
       
  • Variation in concentration of dissolved silicate in the Eastern Philippine
           deep sea

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      Abstract: Abstract Upper Circumpolar Deep Water (UCDW) and North Pacific Deep Water (NPDW) coexist in the upper deep layer (i.e., with a 1.2–2.0-°C potential temperature range and a 2 000–4 100-dbar pressure range) of the Eastern Philippine Sea. They have similar properties in potential temperature and salinity, while have a significant difference in dissolved silicate. Based on the repeated observations along a 137°E transect from the World Ocean Database (WOD18), this study revealed the interannual variability of dissolved silicate in the upper deep layer of the Eastern Philippine Sea. Dissolved silicate increased in 1995, 1996, 2005, 2006, and 2007, and decreased in 1997, 2000, 2001, 2002, and 2004. Composition analysis showed that the large difference between positive and negative dissolved silicate anomalies occurred mainly at ∼15°N and north of 25°N, with the concentration reaching 4.25 µmol/g. Further analysis indicated that the interannual dissolved silicate variability was related to the zonal current variation in the upper deep layer. The relatively strong (weak) westward current transport increased (decreased) NPDW to the Eastern Philippine Sea, thereby resulting in increased (decreased) dissolved silicate.
      PubDate: 2022-09-20
       
  • Temporal change of plankton size structure preserved by Lugol’s
           solution: a FlowCAM study

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      Abstract: Abstract Plankton size structure is crucial for understanding marine ecosystem dynamics and the associated biogeochemical processes. A fixation step by acid Lugol’s solution has been commonly employed to preserve plankton samples in the field. However, the acid Lugol’s solution can bias the estimation of size structure and the preserved plankton size structure can vary with time. Here, we explore the impact of sample storage time on the size-structure of the plankton community preserved by Lugol’s solution. Two short-term experiments and one long-term experiment were conducted to explore the change of plankton community size structure with the storage time: covering from a week to a month, and to nearly seven months based on particle-size data obtained by continuous Flow Cytometer and Microscope (FlowCAM) measurements. We found a linear change of plankton size with the storage time in short-term periods (less than 3 months) with a decrease of the slope but an increase of the intercept for the normalized biomass size spectrum (NBSS). However, there were opposite trends for NBSS with increasing slope but decreasing intercept after 3 months. The potential causes of the distinct patterns of the NBSS parameters are addressed in terms of the interplay between particle aggregation and fragmentation. We found large changes in plankton biovolume and abundance among different size classes, which may indicate a distinct effect of acid Lugol’s solution on various plankton size classes. The mechanism driving temporal change in the size-structure of the Lugol-fixed plankton community was further discussed in terms of particle aggregation and fragmentation. Finally, we emphasize that the effect of storage time should be taken into account when interpreting or comparing data of plankton community acquired from samples with various storage durations.
      PubDate: 2022-09-01
       
  • New and interesting diatoms from the Shimen Wetwalls, Yunnan Province,
           China. II. The diatom genus Nupela Vyverman & Compère
           (Bacillariophyceae)

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      Abstract: Abstract We detailed the valve morphology of five new species of diatom genus Nupela from wetwall communities in Yunnan Province, China, with light and scanning electron microscope. The five new species demonstrate great variability within the genus, as three of them are biraphid and two are monoraphid. In addition, variation was noted in the structure of internal proximal raphe ends, with some species having anchor-shaped ends and other species have hooked ends. The genus Nupela has grown considerably in 30 years since it was first proposed, going from a monotypic genus to over 85 taxa. Diagnosis of the genus is based on the presence of an external covering over the areolae. We discussed the systematic placement of Nupela within the naviculoid diatoms. Yunnan Province appears to harbor many endemic diatom taxa, and many regions of the province have yet to be studied.
      PubDate: 2022-09-01
       
  • The effect of cylindrospermopsin on the bacterioplankton community: a
           microcosm experiment on water from Dishui Lake, Shanghai, China

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      Abstract: Abstract Eutrophication and climate warming have intensified the global expansion of invasive cyanobacteria such as Cylindrospermopsis spp. and Chrysosporum spp. Cylindrospermopsin (CYN) produced by species of the latter two genera may harm phytoplankton, zooplankton, and fishes. However, effects of CYN on the bacterioplankton community have not been studied. Based on high-throughput sequencing, we explored the effect of CYN on the structure and function of the bacterioplankton community by adding pure CYN to in-situ water collected from a brackish coastal shallow lake: Dishui Lake, China. We found that most bacterioplankton taxa had a certain tolerance potential to CYN, but that high concentrations of CYN (40 µg/L) caused a significant decrease in microbial abundance and functional groups. Of the dominant phyla, Actinobacteria had the strongest tolerance to CYN. Network analysis indicated that CYN caused shifts in the community structure of the bacterioplankton, reducing community stability and structural complexity. High CYN concentrations also reduced the correlation between the different bacterioplankton groups, and the abundances of some bacterial taxa associated with the denitrification function and the process of carbon transfer in the microbial food web were inhibited. Our study provides new insight into the response of the bacterioplankton communities to harmful algal toxins produced by cyanobacteria.
      PubDate: 2022-09-01
       
  • Identification of suitable reference genes for quantitative gene
           expression analysis in clam Cyclina sinensis under salinity stress and
           Vibrio infection

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      Abstract: Abstract The appropriate reference gene is a prerequisite for accurate normalization of gene expression level, and research on suitable reference genes in clam Cyclina sinensis is scarce. To improve the situation, we selected five commonly used housekeeping genes, including β-actin, Elongation factor 1-α (EF1-α), Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), 40S ribosomal protein S18 (RPS18), and Tubulin α (TUB-α), then evaluated their expression stability in different adult tissues and under different experimental treatments (salinity stress and Vibrio parahaemolyticus infection). Their expression stability was analyzed by three frequently used programs, geNorm, NormFinder, and BestKeeper. This analysis indicated that multiple genes should be used for normalization, and we concluded that the reference gene combination GAPDH-RPS18-β-actin, should be used for qRT-PCR analysis in different tissues of C. sinensis under normal physiological conditions. For the clams under salinity stress and Vibrio infection, EF1-α-GAPDH-RPS18 was recommended as the gene combination for qRT-PCR normalization. TUB-α was generally poorly ranked by all programs, and should not be used in future studies. This study should provide fundamental support for accurate quantitative gene expression analysis of this species.
      PubDate: 2022-09-01
       
  • Proteomic analysis provides insights into the function of Polian vesicles
           in the sea cucumber Apostichopus japonicus post-evisceration

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      Abstract: Abstract The Polian vesicle is the main accessory structure in the water vascular system of sea cucumbers. It can function to hold water vascular fluid under slight pressure and act as a hematopoiesis, excretory, and inflammatory response organ. Being the only organ to remain after evisceration, the Polian vesicle may function in the survival and regeneration of sea cucumber. We performed Tandem Mass Tag (TMT)-based proteomics to identify how proteins in the Polian vesicle of Apostichopus japonicus respond to evisceration. Among the 8 453 proteins identified from vesicle samples before evisceration (PV0h) and at 6-h post-evisceration (PV6h) and 3-d post-evisceration (PV3d), we detected 222 differentially abundant proteins (DAPs). Most of the annotated DAPs were associated with cell growth and proliferation, immune response and wound healing, substance transport and metabolism, cytoskeleton/cilia/flagella, extracellular matrix, energy production and conversion, protein synthesis and modification, and signal recognition and transduction. Compared with PV0h, fewer DAPs were identified at PV6h, and more DAPs were found at PV3d, and these DAPs were widely distributed among multiple biological processes. Our results indicate that a wide range of biological processes was induced in Polian vesicles in response to evisceration. In particular, Polian vesicles may play important roles in the restoration of coelomocytes, immune defense, and wound healing in sea cucumber. We propose that the Polian vesicle may be involved in visceral regeneration through nutrition and energy supply and by promoting dedifferentiation and migration. Together, these results provided new insights into the function of the Polian vesicle in A. japonicus post-evisceration.
      PubDate: 2022-09-01
       
  • Seasonal shifts in assembly dynamics of phytoplankton communities in a
           humans-affected river in NE China

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      Abstract: Abstract Identifying seasonal shift in phytoplankton community is essential for understanding the significance of eutrophication and finding biological indicators of ecological health of a lotic system. Phytoplankton communities, as well as the seasonal changes in the Ashi River Basin (ASRB) of Heilongjiang Province were investigated from April 2018 to January 2019. A survey in April (spring), July (summer), October (autumn), and January (winter) at 16 sampling sites was conducted. The composition, abundance, and biodiversity indices of phytoplankton were studied and 127 taxa of phytoplankton were identified. Among them, Bacillariophyta dominated the phytoplankton communities in the whole year. There were significant spatio-temporal changes in the structures of the phytoplankton communities during the study period. Trophic state index (TSI) show that the nutritional status of the ASRB was at mesotrophic-middle eutrophic levels. Redundancy analysis (RDA) revealed that total nitrogen (TN), water temperature (WT), oxidation reduction potential (ORP), pH, and dissolved oxygen (DO) were the critical factors in the dynamic phytoplankton community structure. The multivariate regression tree (MRT) analysis showed that Chlamydomonas microsphaerella Pascher et Jahoda, Melosira granulata (Ehrenberg) Ralfs, Merismopedia tenuissima Lemmermann, and Asterionella formosa Hassall were valuable indicators in the determination of water quality in ASRB. Our findings provide a scientific basis for water quality protection and management at basin scale.
      PubDate: 2022-09-01
       
  • Tidal water exchanges can shape the phytoplankton community structure and
           reduce the risk of harmful cyanobacterial blooms in a semi-closed lake

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      Abstract: Abstract For estuaries, inland lakes play a vital role in the ecological balance under the impact of tides. The effect of tides-induced water exchange on phytoplankton community in a semi-closed lake was studied and compared with that of an adjacent closed lake in the Oujiang River mouth in Zhejiang, East China Sea, from June 29, 2020 to June 14, 2021. Results show that the dominant species, abundance, dominance, and diversity of the phytoplankton species between the two lakes were significantly different. In the closed lake, cyanobacteria were the dominant species during the study period. However, in the semi-closed lake, the diversification of the dominant species was greater, and some species of diatoms and green algae became dominant. The average phytoplankton abundance in the closed lake was 6 times of that in the semi-closed lake. The average dominance of cyanobacteria in the closed lake was 0.96, and those in the semi-closed lake and the Oujiang River were 0.51 and 0.22, respectively. Cyanobacterial blooms occurred throughout the study time in the closed lake but not in the semi-closed one. Furthermore, the species diversity richness of the phytoplankton in the semi-closed lake was higher than that of the closed one, and the phytoplankton community between the closed lake and semi-closed lake could be divided into distinctly different groups based on non-metric multidimensional scaling analysis (NMDS) and analysis of similarities (ANOSIM) analysis. The salinity of the water was significantly greater and the transparency significantly smaller in the semi-closed lake than those in the closed lake. Therefore, water exchange driven by local tidal movement increased salinity and decreased transparency of water, which consequently shaped the community structures of different phytoplankton and reduced the risk of a cyanobacterial bloom outbreak in the semi-closed lake.
      PubDate: 2022-08-30
       
  • Marine antifouling behavior of the surfaces modified by dopamine and
           antibacterial peptide

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      Abstract: Abstract Marine biofouling causes serious harms to surfaces of marine devices in transportation, aquaculture, and offshore construction. Traditional antifouling methods pollute the environment. A novel and green antifouling strategy was developed to prevent effectively the adhesion of bacteria and microalgae. An antifouling surface was fabricated via coating Turgencin BMox2 (TB) onto dopamine-modified 304 stainless steel (304 SS). The surface physical and chemical properties before and after modification were characterized by Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectrometer (XPS), contact angle measurement (CA), 3D optical profilometer, ellipsometer, and atomic force microscope (AFM). Antimicrobial peptide was coated onto the surface of 304 SS successfully, and the surface morphology and wettability of the modified sample were modified. Moreover, cytocompatibility of the peptide was evaluated by co-culture of peptide and cells, indicating promising cell biocompatibility at the modified sample surface. At last, antifouling performance and electrochemical corrosion were tested. Results show that the adhesion rates of Vibrio natriegens and Phaeodactylum tricornutum on the antifouling surface were reduced by 99.85% and 67.93%, respectively from those of untreated samples. Therefore, the modified samples retained superior corrosion resistance. The study provide a simply and green way against biofouling on ship hulls and marine equipment.
      PubDate: 2022-08-30
       
  • Pollution characteristics and risk assessment of organophosphate esters in
           aquaculture farms and natural water bodies adjacent to the Huanghe River
           delta

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      Abstract: Abstract To date, little attention has been paid to the effects of organophosphate esters (OPEs) pollution on aquacultural environment and aquatic product safety. Huanghe (Yellow) River delta area is one of the largest aquaculture centers in China, where ecological security protection is crucial in the national strategy of China. To explore the pollution characteristics, bioaccumulation, and health risks of OPEs in aquaculture farms in the Huanghe River delta and natural water bodies in the adjacent seas, five species of organisms from different farm types nearby the Huanghe River delta, and the corresponding culture water and sediments were sampled in this study. The total concentrations of ∑13OPEs in water, sediments, and organisms were 51.53–272.18 ng/L, 52.63–63.17 ng/g dry weight (dw), and 46.82–108.90 ng/g dw, respectively. Among the five types of culture ponds, the water samples from the swimming crab and hairy crab culture ponds exhibited higher OPEs, the concentration of OPEs in the sediments from the few ponds was relatively balanced, and the OPEs in the organism from the holothurian ponds was higher. Tris (1,3-dichloro-2-isopropyl phosphate) (TDCP) was the main contaminant in water samples and tripropyl phosphate (TPrP) in sediments and organisms. However, trisphenyl phosphate (TPhP) showed the strongest bioaccumulation ability, followed by 2-ethylhexyl diphenyl phosphate (EHDPP) and TPrP. The bioaccumulation capacities of the five species were as follows: prawn > holothurian > hairy crab > swimming crab > carp. These five types of organisms, as main seafood in human consumption, were at low risk of negative impacts of pollution. However, the risk from the mixture of organophosphate flame retardants (OPFRs) still requires more attention due to the increasing consumption and production in the world.
      PubDate: 2022-08-30
       
  • Microplastic pollution and enrichment of distinct microbiota in sediment
           of mangrove in Zhujiang River estuary, China

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      Abstract: Abstract The microbial communities colonized on microplastics (MPs) have attracted widespread attention. However, few studies focused on the MPs impacts on mangrove ecosystems, particularly on bacterial communities. We investigated the MPs pollution in mangrove of Zhujiang (Pearl) River estuary (ZRE). To study the potential risk posed by MPs to the mangrove ecosystems, the differences in bacterial communities, functions, and complexity between MPs and sediment samples were reported for the first time. Microplastics (2 991±1 586 items/kg dry weight (dw)) in sediment were mainly fibers and polyethylene, mostly transparent, and in size less than 0.5 mm. Bacterial communities and functions significantly differed from MPs in mangrove sediment. Compared with sediment, MPs significantly enriched members of Proteobacteria, Bacteroidetes, and Actinobacteria, as well as the bacteria associated with plastic-degrading and human diseases on their surface, suggesting that microbial communities on MPs may promote MPs degradation and the spread of diseases, posing potential risk to mangrove ecosystems and human health. Although bacteria on MPs exhibited a lower diversity, the co-occurrence network analysis indicated that network of bacteria colonized on MPs was bigger and more complex than those of mangrove sediment, illustrating that MPs can act as a distinct habitat in this special ecosystem. This study provides a new perspective for increasing our understanding of microplastic pollution in mangrove ecosystems.
      PubDate: 2022-08-30
       
  • Effect of light intensity on bound EPS characteristics of two Microcystis
           morphospecies: the role of bEPS in the proliferation of Microcystis

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      Abstract: Abstract Bound extracellular polymeric substances (bEPS) play an important role in the proliferation of Microcystis. However, the understanding of bEPS characterization remains limited. In this study, three-dimensional fluorescence excitation-emission matrix (3D-EEM) spectroscopy and zeta potentiometer were used to characterize the loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) from two dominant Microcystis morphospecies from Taihu Lake (China) at different light intensities. Physiochemical analysis showed that the growth and TB-EPS or bEPS contents in Microcystis aeruginosa were higher than those in Microcystis flos-aquae at each light intensity. The 3D-EEM contour demonstrated that the intensities of peak B (tryptophan-like substances) in the TB-EPS from M. aeruginosa were stronger than those from M. flos-aquae when the light intensity was higher than 10 µE/(m2·s). Zeta potential analysis showed that the absolute values of the zeta potential of TB-EPS in the two species both increased with rising light intensity, except those of TB-EPS in M. aeruginosa at 105 µE/(m2·s). Moreover, the absolute values of the zeta potential of M. aeruginosa were higher than those of M. flos-aquae at each light intensity. All these results indicated that M. aeruginosa may more quickly proliferate than M. flos-aquae through increased negative charges, bEPS contents, growth, and tryptophan-like substance contents at certain light intensities.
      PubDate: 2022-08-30
       
  • Responses of phytoplankton and its satellite bacteria to exogenous ethanol

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      Abstract: Abstract The response of phytoplankton and its satellite bacteria to various concentrations (0.01%–10% v/v) of ethanol is studied. To elucidate the effect of ethanol, single-strains of phytoplankton (SSP) culture, pure strains of satellite bacteria isolated from nonaxenic SSP cultures, and Escherichia coli were screened. Results indicate that ethanol could promote the growth and photosynthetic efficiency (Fv/Fm) of SSP at 0.01% and the growth of satellite bacteria at 0.01%–1%. Nevertheless, ethanol inhibited the growth and Fv/Fm of SSP at 0.1%–1%, and killed bacteria and SSP at 10% concentration. Further investigation on a satellite bacterium (Mameliella alba) revealed that ethanol promotes growth by serving as a growth stimulant rather than a metabolic carbon source. The 16S rRNA gene amplicon indicated that all nonaxenic SSP cultures harbor distinct satellite bacteria communities where the SSP culture of Skeletonema costatum, Phaeodactylum tricornutum, and Dunaliella bardawil were dominated by bacteria genera of Marivita (∼80%), Dinoroseobacter (∼47%), and Halomonas (∼87%), respectively, indicating that every SSP cultures have their own distinct satellite bacterial community. The bacteria family Rhodobacteraceae was dominant in the two marine diatoms, whereas Halomonadaceae was dominant in the saline green microalga. Compared to their respective controls, the supply of 0.5% ethanol to SSP cultures promoted the growth of the satellite bacteria but did not cause a significant difference in species composition of satellite bacteria. Therefore, a low concentration of ethanol can promote the growth of bacteria in a non-selective way. This study enriched our knowledge about the effect of ethanol on aquatic microbes and provided a baseline for basic and applied biotechnological research in the aquatic environment in the future.
      PubDate: 2022-08-30
       
  • Key physiological traits and chemical properties of extracellular
           polymeric substances determining colony formation in a cyanobacterium

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      Abstract: Abstract Colony formation of cyanobacteria is crucial for the formation of surface blooms in lakes. However, the underlying mechanisms of colony formation involving in physiological and cell surface characteristics remain to not well be established. Six cyanobacterial Microcystis strains (including both unicellular and colonial ones) were employed to estimate the influences of their physiological traits and the composition of extracellular polymeric substances (EPS) on colony or aggregate formation. Results show that raising the number of the photosynthetic reaction center and light-harvesting antenna in the PSII and reducing the growth rate were the major physiological strategies of Microcystis to produce excess EPS enhancing colony formation. Tightly bound EPS (T-EPS) was responsible for colony formation, which approximately accounted for 50% of the total amount of EPS. Five fluorescent components (protein-, tryptophan-, and tyrosine-like components and two humic-like components) were found in the T-EPS, although the amounts of these components varied with strains. Importantly, colonial strains contained much higher tyrosine-like substances than unicellular ones. We suggest that tyrosine-like substances might serve as a crosslinking agent to connect other polymers in EPS (e.g., proteins or polysaccharides) for colony formation. Our findings identified key physiological traits and chemical components of EPS for colony formation in Microcystis, which can contribute to a better understanding on the formation of Microcystis blooms.
      PubDate: 2022-08-30
       
  • Effect of high light and desiccation on photosystem II in the seedlings
           and mature plants of tropical seagrass Enhalus acoroides during low tide

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      Abstract: Abstract During low tide, the intertidal seagrass Enhalus acoroides is often exposed to high light and desiccation, which can seriously threaten its survival, at least partly by inhibiting photosystem II (PSII) activity. The response of leaves of E. acoroides to high light and desiccation was compared for seedlings and mature plants. Results show that the resistance of seedling and mature leaves to high light was quite similar, but to desiccation was very different. Seedling leaves were more sensitive to desiccation than the mature plant leaves, but had better water retention. The damage of desiccation to seedling leaves was mainly caused by dehydration, whereas that to mature plant leaves was caused by hypersaline toxicity. The recovery rate of PSII of seedling leaves was significantly slower than that of the mature plants after the stresses disappeared, which may at least partly contribute to seedling mortality in the wild. In addition, compared to high light, desiccation seriously inhibited the recovery rate of PSII activities even if the leaves became fully rehydrated to their normal relative water content (RWC) in the following re-immersion. Desiccation inhibited the recovery rate of RC/CSM (reaction center per cross section (at \(t = {t_{{F_{\rm{m}}}}}\) )) to decrease the production of assimilatory power, which maybe the cause of the slower PSII recovery in desiccation treatments. This study demonstrates that desiccation particularly coupling with high light have a very negative effect on the PSII of E. acoroides during low tide and the sensitivity of seedlings and mature plants to desiccation is significantly different, which have important reference significance to choose an appropriate transplanting depth where seedlings and mature plants of E. acoroides not only receive sufficient light for growth, but also that minimize desiccation stress during low tide.
      PubDate: 2022-08-30
       
 
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