Degradation of paralytic shellfish toxins during flocculation of Alexandrium pacificum by an oxidized modified clay: A laboratory experiment.

Paralytic shellfish toxins (PSTs), produced by Alexandrium pacificum in the marine environment, are a group of potent neurotoxins which specifically block voltage-gated sodium channels in excitable cells. During the toxigenic A. pacificum blooms outbreaks, PSTs can be accumulated through the food chain and finally enter the human body, posing a significant threat to human health and safety. This study experimented with a novel type of oxidized modified clay, potassium peroxymonosulfate modified clay (PMPS-MC), which could remove A. pacificum cells as well as reduce intracellular and extracellular PSTs toxicity rapidly. For the extracellular PSTs, its content decreased to below the detection limit rapidly through oxidative degradation within 15 min of 10 mg/L PMPS-MC treatment. Whereafter, although the residual cells in water column and some viable cells in flocculated sediment continued to secrete toxins, the extracellular PSTs content and toxicity in the PMPS-MC treatment groups remained significantly lower than those in the control group. For the intracellular PSTs, PMPS-MC might induce the transformation of more toxic GTX1&4 to less toxic GTX2&3 and C1&2, resulting in intracellular PSTs toxicity reduced within 15 min. In addition, intracellular PSTs content and toxicity in the PMPS-MC treatment groups were consistently lower than the control group within 48 h, possibly by inhibiting the A. pacificum cells growth. These results will provide a scientific basis for the field application of modified clay to control A. pacificum blooms.

The synthesis of an acrylamide copolymer and its synergistic effects on clay flocculation of red tide organisms.

The modified clay (MC) method is a common emergency treatment technology for red tides, and the selection of surface modifiers is the key to the MC technology. A cationic polymeric modifier, the copolymer of dimethyl diallyl ammonium chloride and acrylamide (P (DMDAAC-co-AM), PDA) was optimized via a visible-light-induced polymerization technique. The PDA-modified clay (PDAMC) was prepared with strong salt tolerance and achieved efficiencies of 86% at the concentration of 50 mg L-1, and the dose was 90% lower than that of aluminum polychloride-modified clay (PACMC). While polyacrylamide and commercial PDA can achieve efficiencies of only 25 and 67%, respectively, but high doses were required. This is because PDA changed the surface charges of clay particles from negative to positive, which promotes the formation of the polymer-chains bridging network to overcome the difficulties of curling in seawater. According to the analysis of flocculation parameters and spatial conformation of PDAMC, the high salinity tolerance of the PDAMC was attributed to the synergistic processes of charge neutralization and the three-dimensional network bridging. Therefore, this study has developed a highly effective flocculant material used in seawater and provided an important reference for the management of red tide organisms.

The molecular mechanisms and environmental effects of modified clay control algal blooms in aquacultural water.

Modified clay (MC) technology is an effective method for controlling harmful algal blooms (HABs). Based on field experience, a bloom does not continue after treatment with MC, even though the residual HAB biomass accounts for 20-30% of the initial biomass. Laboratory studies using unialgal cultures have found that MC could inhibit the growth of the residual algal cells to prevent HABs. Nevertheless, the phytoplankton in field waters is diverse. Therefore, unclassified complex mechanisms may exist. To illustrate the molecular mechanisms through which MC controls HABs in the field and verify the previous laboratory findings, a series of experiments and bioinformatics analyses were conducted using bloom waters from aquacultural ponds. The results showed that a 72.29% removal efficiency of algal biomass could effectively control blooms. The metatranscriptomic results revealed that the number of downregulated genes (131,546) was greater than that of upregulated genes (24,318) at 3 h after MC addition. Among these genes, several genes related to DNA replication were downregulated; however, genes involved in DNA repair were upregulated. Metabolism-related pathways were the most significantly upregulated (q < 0.05), including photosynthesis and oxidative phosphorylation. The results also showed that MC reduced most of the biomass of the dominant phytoplankton species, likely by removing apical dominance, which increased the diversity and stability of the phytoplankton community. In addition to reducing the pathogenic bacterial density, MC reduced the concentrations of PO43- (96.22%) and SiO32- (66.77%), thus improving the aquaculture water quality, altering the phytoplankton community structure (the proportion of Diatomea decreased, and that of Chlorophyta increased), and inhibiting phytoplankton growth. These effects hindered the rapid development of large phytoplankton biomasses and allowed the community structure to remain stable, reducing HAB threats. This study illustrates the molecular mechanisms through which MC controls HABs in the field and provides a scientific method for removing HABs in aquacultural waters.

A New Perspective: Revealing the Algicidal Properties of Bacillus subtilis to Alexandrium pacificum from Bacterial Communities and Toxins.

Algicidal bacteria are important in the control of toxic dinoflagellate blooms, but studies on the environmental behavior of related algal toxins are still lacking. In this study, Bacillus subtilis S3 (S3) showed the highest algicidal activity against Alexandrium pacificum (Group IV) out of six Bacillus strains. When treated with 0.5% (v/v) S3 bacterial culture and sterile supernatant, the algicidal rates were 69.74% and 70.22% at 12 h, respectively, and algicidal substances secreted by S3 were considered the mechanism of algicidal effect. During the algicidal process, the rapid proliferation of Alteromonas sp. in the phycosphere of A. pacificum may have accelerated the algal death. Moreover, the algicidal development of S3 released large amounts of intracellular paralytic shellfish toxins (PSTs) into the water, as the extracellular PSTs increased by 187.88% and 231.47% at 12 h, compared with the treatment of bacterial culture and sterile supernatant at 0 h, respectively. Although the total amount of PSTs increased slightly, the total toxicity of the algal sample decreased as GTX1/4 was transformed by S3 into GTX2/3 and GTX5. These results more comprehensively reveal the complex relationship between algicidal bacteria and microalgae, providing a potential source of biological control for harmful algal blooms and toxins.

Profiles of and variations in aluminum species in PAC-MC used for the removal of blooming microalgae.

Polyaluminum chloride modified clay (PAC-MC) is a safe and efficient red tide control agent that has been studied and applied worldwide. Although it is well known that the distribution of hydrolytic aluminum species in PAC affects its flocculation, little is known about the influence of particulars aluminum species on the microalgae removal efficiency of PAC-MC; this lack of knowledge creates a bottleneck in the development of more efficient MCs based on aluminum salts. The ferron method was used in this study to quantitatively analyze the distributions of and variations in different hydrolytic aluminum species during the process of microalgae removal by PAC-MC. The results showed that Ala, which made up 5%-20% of the total aluminum, and Alp, which made up 15%-55% of the total aluminum, significantly affected microalgae removal, with Pearson's correlation coefficients of 0.83 and 0.89, respectively. Most of the aluminum in the PAC-MC sank rapidly into the sediments, but the rate and velocity of settlement were affected by the dose of modified clay. The optimal dose of PAC-MC for precipitating microalgae was determined based on its aluminum profile. These results provide guidance for the precise application of PAC-MC in the control of harmful algal blooms.

Programmed cell death induced by modified clay in controlling Prorocentrum donghaiense bloom.

Modified clay (MC), an effective material used for the emergency elimination of algal blooms, can rapidly reduce the biomass of harmful algal blooms (HABs) via flocculation. After that, MC can still control bloom population through indirect effects such as oxidative stress, which was initially proposed to be related to programmed cell death (PCD) at molecular level. To further study the MC induced cell death in residual bloom organisms, especially identifying PCD process, we studied the physiological state of the residual Prorocentrum donghaiense. The experimental results showed that flocculation changed the physiological state of the residual cells, as evidenced by growth inhibition and increased reactive oxygen species production. Moreover, this research provides biochemical and ultrastructural evidence showing that MC induces PCD in P. donghaiense. Nuclear changes were observed, and increased caspase-like activity, externalization of phosphatidylserine and DNA fragmentation were detected in MC-treated groups and quantified. And the mitochondrial apoptosis pathway was activated in both MC-treated groups. Besides, the features of MC-induced PCD in a unicellular organism were summarized and its concentration dependent manner was proved. All our preliminary results elucidate the mechanism through which MC can further control HABs by inducing PCD and suggest a promising application of PCD in bloom control.

Molecular Mechanism of Modified Clay Controlling the Brown Tide Organism Aureococcus anophagefferens Revealed by Transcriptome Analysis.

The data and experiences in mitigating harmful algal blooms (HABs) by modified clay (MC) show that a bloom does not continue after the dispersal of the MC, even though the density of the residual cells in the water is still high, at 20-30% of the initial cell density. This interesting phenomenon indicates that in addition to flocculation, MC has an additional control mechanism. Here, transcriptome sequencing technology was used to study the molecular mechanism of MC in controlling HABs. In residual cells treated with MC, the photosynthetic light reaction was the most affected physiological process. Some genes related to the light harvesting complex, photosystem (PS) I and PS II, were significantly up-regulated ( p < 0.05), and several transcripts increased by as much as 6-fold. In contrast, genes associated with the dark reaction did not significantly change. In addition to genes associated with photosynthesis, numerous genes related to energy metabolism, stress adaptation, cytoskeletal functioning, and cell division also responded to MC treatment. These results indicated that following treatment with MC, the normal physiological processes of algal cells were disrupted, which inhibited cell proliferation and growth. Thus, these findings provide scientific proof that HABs are controlled by MC.

Insights into the differential removal of various red tide organisms using modified clay: Influence of biocellular properties and mechanical interactions.

In recent years, red tides have increased worldwide in frequency, intensity, involving a higher number of causative species during the events. As the most commonly used method for control of red tides, modified clay (MC) was found to have differential ability to remove various red tide species. However, the underlying mechanisms have not yet been completely elucidated. In this study, the use of MC to remove three typical disaster-causing species, Aureococcus anophagefferens, Prorocentrum donghaiense and Heterosigma akashiwo, was investigated, and differential removal of these species was probed with insights into their biocellular properties and mechanical interactions. The results showed that removal efficiencies of the three species by MC decreased in the order P. donghaiense > A. anophagefferens > H. akashiwo, while the sedimentation rates decreased in the order H. akashiwo > P. donghaiense > A. anophagefferens. Analyses of the cell surface properties and redundancy analysis (RDA) revealed that the highest surface zeta potential of -5.32±0.39 mV made P. donghaiense the most easily removed species; the smallest cell size of 3.30±0.03 µm facilitated the removal of A. anophagefferens; and the highest hydrophobicity with a H2O surface contact angle of 98.50±4.31° made the removal of H. akashiwo difficult. X-ray photoelectron spectroscopy (XPS) data indicated that the electronegativity of P. donghaiense was caused by carboxyl groups and phosphodiester groups, and the hydrophobicity of H. akashiwo was associated with a high C-(C, H) content on the cell surface. According to the extended Derjaguin, Landau, Verwey, and Overbeek (ex-DLVO) theory calculation, differences in the interaction energies between MC and the three red tide species effectively explained their different sedimentation rates. In addition, the degree of oxidative damage caused by MC to the three red tide species differed, which also affected the removal of red tide organisms.

Key biogeochemical processes and source apportionment of nitrate in the Bohai Sea based on nitrate stable isotopes.

Excessive nitrate input is one of the primary factors causing nearshore eutrophication. This study applied the nitrate stable isotope techniques to analyse the biogeochemical processes and sources of nitrate in the Bohai Sea (BHS). The results showed that intensive NO3- assimilation probably occurred at surface in summer, while nitrification primarily occurred in the Yellow River diluted water. In autumn, regional assimilation and nitrification were still identified. For avoiding the interference from assimilation, the isotopic fractionations were further calculated as correction data for the quantitative analysis of nitrate sources. The river inputs were identified as the primary source of nitrate in the BHS in summer and autumn, accounting for >50 %, and the atmospheric deposition was the secondary source. This study provides quantitative data for evaluating the significance of river inputs to the nearshore nitrate, which will be beneficial to policy formulation on the BHS eutrophication control.

BTXs removals by modified clay during mitigation of Karenia brevis bloom: Insights from adsorption and transformation.

Harmful algal blooms (HABs), especially those caused by toxic dinoflagellates, are spreading in marine ecosystems worldwide. Notably, the prevalence of Karenia brevis blooms and potent brevetoxins (BTXs) pose a serious risk to public health and marine ecosystems. Therefore, developing an environmentally friendly method to effectively control HABs and associated BTXs has been the focus of increasing attention. As a promising method, modified clay (MC) application could effectively control HABs. However, the environmental fate of BTXs during MC treatment has not been fully investigated. For the first time, this study revealed the effect and mechanism of BTX removal by MC from the perspective of adsorption and transformation. The results indicated that polyaluminium chloride-modified clay (PAC-MC, a typical kind of MC) performed well in the adsorption of BTX2 due to the elevated surface potential and more binding sites. The adsorption process was a spontaneous endothermic process that conformed to pseudo-second-order adsorption kinetics (k2 = 6.8 × 10-4, PAC-MC = 0.20 g L-1) and the Freundlich isotherm (Kf = 55.30, 20 °C). In addition, detailed product analysis using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) indicated that PAC-MC treatment effectively removed the BTX2 and BTX3, especially those in the particulate forms. Surprisingly, PAC-MC could promote the transformation of BTX2 to derivatives, including OR-BTX2, OR-BTX3, and OR-BTX-B5, which were proven to have lower cytotoxicity.

Phycosphere bacterial composition and function in colony and solitary Phaeocystis globosa strains providing novel insights into the algal blooms.

Phycosphere bacteria can regulate the dynamics of different algal blooms that impact marine ecosystems. Phaeocystis globosa can alternate between solitary free-living cells and colonies and the latter morphotype is dominate during blooms. The mechanisms underlying the formation of these blooms have received much attention. High throughput sequencing results showed that the bacterial community composition differed significantly between colony and solitary strains in bacterial composition and function. It was found that the genera SM1A02 and Haliea were detected only among the colony strains and contribute to ammonium accumulation in colonies, and the genus Sulfitobacter was abundant among the colony strains that were excellent at producing DMS. In addition, the bacterial communities of the two colony strains exhibited stronger abilities for carbon and sulfur metabolism, energy metabolism, vitamin B synthesis, and signal transduction, providing inorganic and organic nutrients and facilitating tight communication with the host algae, thereby promoting growth and bloom development.

Uncovering nutrient regeneration, transformation pattern, and its contribution to harmful algal blooms in mariculture waters.

The prevalence of harmful algal blooms (HABs), especially in mariculture waters, has become a concern for environmental and human health worldwide. Notably, the frequent occurrence of HABs relies upon a substantial supply of available nutrients, which are influenced by nutrient recycling. However, nutrient regeneration, transformation pattern, and their contribution to HABs in mariculture waters remain largely unknown. In this study, by combining field investigation and incubation experiments from June to September 2020, the temporal variations in nutrients and algal composition were revealed. In addition, the nutrient regeneration and assimilation rates in the water column during two continuous algal blooms were measured. The results indicated that organic nutrients, which were the dominant components, strongly stimulated nutrient regeneration. High regeneration rates were observed, with dissolved inorganic nitrogen (DIN) and phosphorous (DIP) regeneration rates ranging from 0.25 to 2.64 µmol/L·h and 0.01 to 0.09 µmol/L·h, respectively. Compared to the direct uptake of organic nutrients, the rapid regeneration of inorganic nutrients played a vital role in sustaining continuous algal blooms, as regenerated DIN contributed 100 % while regenerated DIP contributed 72-100 % of the algal assimilation demand. Furthermore, the redundancy analysis and inverse solution equations indicated that different N transformation patterns and utilization strategies occurred during Heterosigma and Nannochloris blooms. The shorter N recycling pathway and faster NH4+ supply rates provided favorable conditions for the dominance of Nannochloris over Heterosigma, which had a preference for the uptake of NO3-. In conclusion, we propose that nutrient regeneration is a key maintenance mechanism underlying the maintenance of continuous algal blooms, and different N transformation patterns and utilization strategies regulate algal communities in mariculture waters.

Insights into how characteristics of dissolved algal organic matter affect the efficiency of modified clay in controlling harmful algal blooms.

Dissolved algal organic matter (dAOM) originating from harmful algal blooms (HABs) can deteriorate the quality of municipal water supplies, threaten the health of aquatic environments, and interfere with modified clay (MC)-based HABs control measures. In this study, we explored the composition of dAOM from Prorocentrum donghaiense, a typical HAB organism, and assessed the influence of dAOM on MC flocculation. Our results suggested that dAOM composition was complex and had a wide molecular weight (MW) distribution. MW and electrical properties were important dAOM characteristics affecting flocculation and algal removal efficiency of MC. Negatively charged high-MW components (>50 kDa) critically affected algal removal efficiency, reducing the zeta potential of MC particles and leading to small and weak flocs. However, the effect of dAOM depended on its concentration. When the cell density of P. donghaiense reached HAB levels, the high-MW dAOM strongly decreased the algal removal efficiency of MC.

Chromosome-scale genome assembly reveals insights into the evolution and ecology of the harmful algal bloom species Phaeocystis globosa Scherffel.

The phytoplankton Phaeocystis globosa plays an important role in sulfur cycling and climate control, and can develop harmful algal blooms (HABs). Here we report a chromosome-scale reference genome assembly of P. globosa, which enable in-depth analysis of molecular underpinnings of important ecological characteristics. Comparative genomic analyses detected two-rounds of genome duplications that may have fueled evolutionary innovations. The genome duplication may have resulted in the formation of dual HiDP and LoDP dimethylsulphoniopropionate (DMSP) biosynthesis pathways in P. globosa. Selective gene family expansions may have strengthened biological pathways critical for colonial formation that is often associated with the development of algal blooms. The copy numbers of rhodopsin genes are variable in different strains, suggesting that rhodopsin genes may play a role in strain-specific adaptation to ecological factors. The successful reconstruction of the P. globosa genome sets up an excellent platform that facilitates in-depth research on bloom development and DMSP metabolism.

Novel insights into toxin changes associated with the growth of Alexandrium pacificum: Revealing active toxin-secretion ability and toxin cell quota variation.

Paralytic shellfish toxins (PSTs) are widely distributed globally and are produced by Alexandrium pacificum in marine system. However, the characteristics of toxins producing and secreting associated with growth phases are still unclear, especially whether A. pacificum has the ability to actively secrete PSTs is controversial. In this study, variation characteristics of intracellular and extracellular PSTs contents associated with A. pacificum growth phases were investigated thoroughly. The results showed that intracellular and extracellular PSTs contents increased sharply during the exponential phase. But during the stationary phase, the intracellular PSTs content increased by only 26 %, and the extracellular PSTs content did not increase significantly. Since the increase in extracellular PSTs content mainly occurred at the exponential phase, when most cells were living, we speculated that active PSTs secretion of living cells might be an important production pathway of extracellular toxins besides leakage from dead cells. Furthermore, toxin cell quota variation associated with the growth phase was analysed. In the exponential phase, the toxin cell quota first increased and then decreased, with a maximum of 19.02 ± 1.80 fmol/cell at 6 d. However, after entering the stationary phase, this value slowly increased again, suggesting that vigilance should be raised for the plateau of Alexandrium blooms. In addition, cells in the exponential phase mainly produced O-sulfated components such as GTX1&4, cells in the stationary phase mainly produced O-sulfate-free components such as GTX5. In this study, the toxigenic rules of A. pacificum were comprehensively uncovered, which provided theoretical guidance for the prevention and mitigation of A. pacificum blooms.

Nitrate dynamics and source apportionment on the East China Sea shelf revealed by nitrate stable isotopes and a Bayesian mixing model.

The excess input of nitrate is one of the primary factors triggering nearshore eutrophication. To estimate the source apportionment of nitrate on the East China Sea (ECS) shelf, the nitrogen and oxygen stable isotopes in nitrate (δ15N-NO3- and δ18O-NO3-) collected in winter and late spring 2016 were analyzed alongside essential physical, chemical and biological parameters. The temporal and spatial distributions and characteristic values of nitrate-bearing water masses were presented. Accordingly, the end-member mixing model and Rayleigh model were applied to systematically analyze biogeochemical processes. The biogeochemical processes of nitrate were weak in winter, except in the southern ECS, where assimilation and nitrification probably occurred. In contrast, the biogeochemical processes were intensive in spring. The stable isotopic fractionations of N and O were unified in the whole area, and the ratio between δ18O-NO3- and δ15N-NO3- was 1.81 ± 0.04, which indicated significant assimilation accompanying nitrification in spring. Furthermore, a Bayesian stable isotope mixing model was used to reveal the source contributions of nitrate on the ECS shelf for the first time, demonstrating that the Changjiang Diluted Water and Kuroshio Subsurface Water were always sustained and provided steady nitrate sources for the whole ECS. The nitrate inputs from the Yellow Sea to the northern ECS increased from approximately 30 % in spring to nearly 70 % in winter, while that from the Taiwan Strait Warm Water to the southern ECS decreased from approximately 40 % in spring to zero in winter. Moreover, although the nitrate contributions from nitrification were significantly weak in the middle and northern ECS during winter, they were important over the entire ECS during spring. This study qualitatively and quantitatively improves the understanding of seasonal nitrate control from various sources, and these findings are important for nutrient management and policy making to mitigate nearshore eutrophication.

Uncovering the regulation effect of modified clay on toxin production in Alexandrium pacificum: From physiological insights.

As a common dinoflagellate, Alexandrium pacificum can produce paralytic shellfish toxins (PSTs). It can be removed from water by Polyaluminium chloride modified clay (PAC-MC), but it is unclear whether PAC-MC can prevent PSTs content and toxicity from increasing and whether PAC-MC can stimulate PSTs biosynthesis by A. pacificum. Effect of PAC-MC on PSTs and the physiological mechanism were analysed here. The results showed total PSTs content and toxicity decreased respectively by 34.10 % and 48.59 % in 0.2 g/L PAC-MC group at 12 days compared with control group. And the restriction of total PSTs by PAC-MC was mainly achieved via inhibition of algal cell proliferation, by affecting A. pacificum physiological processes and changing phycosphere microbial community. Meanwhile, single-cell PSTs toxicity did not increase significantly throughout the experiment. Moreover, A. pacificum treated with PAC-MC tended to synthesize sulfated PSTs such as C1&2. Mechanistic analysis showed that PAC-MC induced upregulation of sulfotransferase sxtN (related to PSTs sulfation), and functional prediction of bacterial community also showed significant enrichment of "sulfur relay system" after PAC-MC treatment, which might also promote PSTs sulfation. The results will provide theoretical guidance for the application of PAC-MC to field control of toxic Alexandrium blooms.

Metabarcoding analysis identifies high diversity of harmful algal bloom species in the coastal waters of the Beibu Gulf.

Harmful algal blooms (HABs) have occurred more frequently in recent years. In this study, to investigate their potential impact in the Beibu Gulf, short-read and long-read metabarcoding analyses were combined for annual marine phytoplankton community and HAB species identification. Short-read metabarcoding showed a high level of phytoplankton biodiversity in this area, with Dinophyceae dominating, especially Gymnodiniales. Multiple small phytoplankton, including Prymnesiophyceae and Prasinophyceae, were also identified, which complements the previous lack of identifying small phytoplankton and those unstable after fixation. Of the top 20 phytoplankton genera identified, 15 were HAB-forming genera, which accounted for 47.3%-71.5% of the relative abundance of phytoplankton. Based on long-read metabarcoding, a total of 147 OTUs (PID > 97%) belonging to phytoplankton were identified at the species level, including 118 species. Among them, 37 species belonged to HAB-forming species, and 98 species were reported for the first time in the Beibu Gulf. Contrasting the two metabarcoding approaches at the class level, they both showed a predominance of Dinophyceae, and both included high abundances of Bacillariophyceae, Prasinophyceae, and Prymnesiophyceae, but the relative contents of the classes varied. Notably, the results of the two metabarcoding approaches were quite different below the genus level. The high abundance and diversity of HAB species were probably due to their special life history and multiple nutritional modes. Annual HAB species variation revealed in this study provided a basis for evaluating their potential impact on aquaculture and even nuclear power plant safety in the Beibu Gulf.

Mechanisms of Phaeocystis globosa blooms in the Beibu Gulf revealed by metatranscriptome analysis.

The haptophyceae Phaeocystis globosa is a species responsible for harmful algal blooms in the global ocean, forming blooms in the Beibu Gulf annually since 2011. This species can alternate between solitary free-living cells and colonies. Colonies are the dominant morphotype during blooms. To date, the underlying mechanism of P. globosa blooms in the Beibu Gulf is poorly understood. After combining results of ecological surveys, laboratory studies, and metatranscriptome and bioinformatics analyses, it was found that low temperatures, high nitrate, and low organic phosphorus induced P. globosa blooms in the Beibu Gulf. Additionally, the unique genetic and physiological characteristics that allow P. globosa to stand out as a dominant species in such an environment include (1) several genes encoding high-affinity nitrate transport proteins that could be highly expressed under sufficient nitrate conditions; (2) energy metabolism genes involved in photosynthesis and oxidative phosphorylation that were actively expressed at low temperatures to carry out carbon and energy reversion and produce sufficient ATP for various life activities, individually; (3) abundant glycan synthesis genes that were highly expressed at low temperatures, thus synthesizing large quantities of proteoglycans to construct the mucilaginous envelope forming the colony; (4) cells in colonies exhibited active gene expression in DNA replication contributing to a faster growth rate, which could help P. globosa occupy niches quickly; and (5) the energy and material expenditure was redistributed in colonial cells accompanied with chitin filaments and flagella degraded, more expenditure was used for the synthesis of the mucilaginous envelope and the rapid proliferation.

Transcriptome profiles of genes related to growth and virulence potential in Vibrio alginolyticus treated with modified clay.

Vibrio alginolyticus is a globally distributed opportunistic pathogen that causes different degrees of disease in various marine organisms, such as fish, shrimp and shellfish. At present, vibriosis caused by V. alginolyticus has a wide epidemic range and causes frequent outbreaks, resulting in substantial losses in aquaculture. According to previous studies, modified clay (MC) could effectively flocculate and reduce the density of Vibrio in water, but it is still unknown whether MC inhibits growth and how it affects virulence in bottom flocs. Here, we studied the response mechanism of V. alginolyticus in flocs treated with MC at the transcriptome level and verified the transcriptomic data combined with relevant physiological experiments and reverse transcription quantitative real-time PCR (RT-qPCR) for the first time. It was found that the morphology of Vibrio in the MC flocs changed, the membrane function was damaged, the antioxidant system was activated, and the material and energy metabolism also changed. In addition, MC could inhibit the expression of virulence factors of V. alginolyticus; for example, flagella, pilus, siderophores, quorum sensing, and other related genes were significantly downregulated. In general, MC effectively inhibited the growth of Vibrio and reduced its virulence potential in flocs, which could provide theoretical support for a new model of healthy aquaculture.