The first evidence of deinoxanthin from Deinococcus sp. Y35 with strong algicidal effect on the toxic dinoflagellate Alexandrium tamarense

Algicidal bacteria-derived membrane vesicles as shuttles mediating cross-kingdom interactions between bacteria and algae

Bacterial membrane vesicles (BMVs) are crucial biological vehicles for facilitating interspecies and interkingdom interactions. However, the extent and mechanisms of BMV involvement in bacterial-algal communication remain elusive. This study provides evidence of BMVs delivering cargos to targeted microalgae. Membrane vesicles (MVs) from Chitinimonas prasina LY03 demonstrated an algicidal profile similar to strain LY03. Further investigation revealed Tambjamine LY2, an effective algicidal compound, selectively packaged into LY03-MVs. Microscopic imaging demonstrated efficient delivery of Tambjamine LY2 to microalgae Heterosigma akashiwo and Thalassiosira pseudonana through membrane fusion. In addition, the study demonstrated the versatile cargo delivery capabilities of BMVs to algae, including the transfer of MV-carried nucleic acids into algal cells and the revival of growth in iron-depleted microalgae by MVs. Collectively, our findings reveal a previously unknown mechanism by which algicidal bacteria store hydrophobic algicidal compounds in MVs to trigger target microalgae death and highlight BMV potency in understanding and engineering bacterial-algae cross-talk.

Insights into the radiation and oxidative stress mechanisms in genus Deinococcus

Deinococcus species, noted for their exceptional resistance to DNA-damaging environmental stresses, have piqued scientists' interest for decades. This study dives into the complex mechanisms underpinning radiation resistance in the Deinococcus genus. We have examined the genomes of 82 Deinococcus species and classified radiation-resistance proteins manually into five unique curated categories: DNA repair, oxidative stress defense, Ddr and Ppr proteins, regulatory proteins, and miscellaneous resistance components. This classification reveals important information about the various molecular mechanisms used by these extremophiles which have been less explored so far. We also investigated the presence or lack of these proteins in the context of phylogenetic relationships, core, and pan-genomes, which offered light on the evolutionary dynamics of radiation resistance. This comprehensive study provides a deeper understanding of the genetic underpinnings of radiation resistance in the Deinococcus genus, with potential implications for understanding similar mechanisms in other organisms using an interactomics approach. Finally, this study reveals the complexities of radiation resistance mechanisms, providing a comprehensive understanding of the genetic components that allow Deinococcus species to flourish under harsh environments. The findings add to our understanding of the larger spectrum of stress adaption techniques in bacteria and may have applications in sectors ranging from biotechnology to environmental research.

Biological and Chemical Approaches for Controlling Harmful Microcystis Blooms

The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O2, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H2O2 are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies.

Metabolomics and Microbiomics Insights into Differential Surface Fouling of Three Macroalgal Species of Fucus (Fucales, Phaeophyceae) That Co-Exist in the German Baltic Sea

The brown algal genus Fucus provides essential ecosystem services crucial for marine environments. Macroalgae (seaweeds) release dissolved organic matter, hence, are under strong settlement pressure from micro- and macrofoulers. Seaweeds are able to control surface epibionts directly by releasing antimicrobial compounds onto their surfaces, and indirectly by recruiting beneficial microorganisms that produce antimicrobial/antifouling metabolites. In the Kiel Fjord, in the German Baltic Sea, three distinct Fucus species coexist: F. vesiculosus, F. serratus, and F. distichus subsp. evanescens. Despite sharing the same habitat, they show varying fouling levels; F. distichus subsp. evanescens is the least fouled, while F. vesiculosus is the most fouled. The present study explored the surface metabolomes and epiphytic microbiota of these three Fucus spp., aiming to uncover the factors that contribute to the differences in the fouling intensity on their surfaces. Towards this aim, algal surface metabolomes were analyzed using comparative untargeted LC-MS/MS-based metabolomics, to identify the marker metabolites influencing surface fouling. Their epiphytic microbial communities were also comparatively characterized using high-throughput amplicon sequencing, to pinpoint the differences in the surface microbiomes of the algae. Our results show that the surface of the least fouling species, F. distichus subsp. evanescens, is enriched with bioactive compounds, such as betaine lipids MGTA, 4-pyridoxic acid, and ulvaline, which are absent from the other species. Additionally, it exhibits a high abundance of the fungal genera Mucor and Alternaria, along with the bacterial genus Yoonia-Loktanella. These taxa are known for producing antimicrobial/antifouling compounds, suggesting their potential role in the observed fouling resistance on the surface of the F. distichus subsp. evanescens compared to F. serratus and F. vesiculosus. These findings provide valuable clues on the differential surface fouling intensity of Fucus spp., and their importance in marine chemical defense and fouling dynamics.

Identification of a Shewanella halifaxensis Strain with Algicidal Effects on Red Tide Dinoflagellate Prorocentrum triestinum in Culture

The dinoflagellate Prorocentrum triestinum forms high biomass blooms that discolor the water (red tides), which may pose a serious threat to marine fauna and aquaculture exploitations. In this study, the algicidal effect of a bacterial strain (0YLH) belonging to the genus Shewanella was identified and evaluated against P. triestinum. The algicidal effects on the dinoflagellate were observed when P. triestinum was exposed to cell-free supernatant (CFS) from stationary-phase cultures of the 0YLH strain. After 24 h exposure, a remarkable reduction in the photosynthetic efficiency of P. triestinum was achieved (55.9%), suggesting the presence of extracellular bioactive compounds produced by the bacteria with algicidal activity. Furthermore, the CFS exhibited stability and maintained its activity across a wide range of temperatures (20-120 °C) and pH values (3-11). These findings highlight the algicidal potential of the bacterium Shewanella halifaxensis 0YLH as a promising tool for the environmentally friendly biological control of P. triestinum blooms.

Impacts of a bacterial algicide on metabolic pathways in Chlorella vulgaris

Chlorella is a dominant species during harmful algal blooms (HABs) worldwide, which bring about great environmental problems and are also a serious threat to drinking water safety. Application of bacterial algicides is a promising way to control HABs. However, the identified bacterial algicides against Chlorella and the understanding of their effects on algal metabolism are very limited. Here, we isolated a novel bacterium Microbacterium paraoxydans strain M1 that has significant algicidal activities against Chlorella vulgaris (algicidal rate 64.38 %, at 120 h). Atrazine-desethyl (AD) was then identified from strain M1 as an effective bacterial algicide, with inhibition or algae-lysing concentration values (EC50) of 1.64 μg/mL and 1.38 μg/mL, at 72 h and 120 h, respectively. LAD (2 μg/mL AD) or HAD (20 μg/mL AD) causes morphology alteration and ultrastructure damage, chlorophyll a reduction, gene expression regulation (for example, psbA, 0.05 fold at 24 h, 2.97 fold at 72 h, and 0.23 fold of the control in HAD), oxidative stress, lipid oxidation (MDA, 2.09 and 3.08 fold of the control in LAD and HAD, respectively, at 120 h) and DNA damage (average percentage of tail DNA 6.23 % at 120 h in HAD, slight damage: 5∼20 %) in the algal cells. The impacts of AD on algal metabolites and metabolic pathways, as well as the algal response to the adverse effects were investigated. The results revealed that amino acids, amines, glycosides and urea decreased significantly compared to the control after 24 h exposure to AD (p < 0.05). The main up-regulated metabolic pathways implied metabonomic resistance and defense against osmotic pressure, oxidative stress, photosynthesis inhibition or partial cellular structure damage, such as phenylalanine metabolism, arginine biosynthesis. The down-regulated glycine, serine and threonine metabolism is a major lead in the algicidal mechanism according to the value of pathway impact. The down-regulated glycine, and serine are responsible for the downregulation of glyoxylate and dicarboxylate metabolism, aminoacyl-tRNA biosynthesis, glutathione metabolism, and sulfur metabolism, which strengthen the algae-lysing effect. It is the first time to highlight the pivotal role of glycine, serine and threonine metabolism in algicidal activities, which provided a new perspective for understanding the mechanism of bacterial algicides exerting on algal cells at the metabolic level.

An insight into algicidal characteristics of Bacillus altitudinis G3 from dysfunctional photosystem and overproduction of reactive oxygen species

Cyanobacterial blooms negatively affect aquatic ecosystems and human health. Algicidal bacteria can efficiently kill bloom-causing cyanobacteria. Bacillus altitudinis G3 isolated from Dianchi Lake shows high algicidal activity against Microcystis aeruginosa. In this study, we investigated its algicidal characteristics including attack mode, photosynthesis responses, and source and the contribution of reactive oxygen species (ROS). The results showed that G3 efficiently and specifically killed M. aeruginosa mainly by releasing both thermolabile and thermostable algicidal substances, which exhibited the highest algicidal activity (99.8%, 72 h) in bacterial mid-logarithmic growth phase. The algicidal ratio under full-light conditions (99.5%, 60 h) was significantly higher than under dark conditions (<20%, P < 0.001). G3 filtrate caused photosystem dysfunction by decreasing photosynthetic efficiency, as indicated by significantly decreased F_v/F_m and PI_ABS (P < 0.001) values. It also inhibited photosynthetic electron transfer as indicated by significantly decreased rETR (P < 0.001), especially Q_A^- downstream, as revealed by significantly decreased φE_o and ψ_o, and increased M_o (P < 0.001). These results indicated that the algicidal activity of G3 filtrate is light-dependent, and the cyanobacterial photosystem is an important target. Cyanobacterial ROS and malondialdehyde contents greatly increased by 37.1% and 208% at 36 h, respectively. ROS levels decreased by 49.2% (9 h) when diuron (3-(3-4-dichlorophenyl)-1,1-dimethylurea) partially blocked photosynthetic electron transport from Q_A to Q_B. Therefore, excessive ROS were produced from disrupted photosynthesis, especially the inhibited electron transport area in Q_A^- downstream, and caused severe lipid peroxidation with significantly increased MDA content and oxidative stress in cyanobacteria. The ROS scavenger N-acetyl-l-cysteine significantly decreased both cyanobacterial ROS levels (34%) and algicidal ratio (52%, P < 0.05) at 39 h. Thus, excessive ROS production due to G3 filtrate administration significantly contributed to its algicidal effect. G3 could be an excellent algicide to control M. aeruginosa blooms in waters under suitable light conditions.

Isolation and characterization of algicidal bacteria from freshwater aquatic environments in China

Algicidal bacteria can inhibit the growth of algae or lyse algal cells, thus playing roles in shaping aquatic microbial communities and maintaining the functions of aquatic ecosystems. Nevertheless, our understanding of their diversities and distributions remains limited. In this study, we collected water samples from 17 freshwater sites in 14 cities in China and screened a total of 77 algicidal bacterial strains using several prokaryotic cyanobacteria and eukaryotic algae as target strains. According to their target-specificities, these strains were classified into three subgroups, cyanobacterial algicidal bacteria, algal algicidal bacteria, and broad-target algicidal bacteria, each displaying distinctive compositions and geographical distribution patterns. They are assigned to Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes bacterial phyla, of which Pseudomonas and Bacillus are the most abundant gram-negative and gram-positive genus, respectively. A number of bacterial strains, such as Inhella inkyongensis and Massilia eburnean, are suggested as new algicidal bacteria. The diverse taxonomies, algal-inhibiting abilities and distributions of these isolates have suggested that there are rich algicidal bacterial resources in these aquatic environments. Our results provide new microbial resources for algal-bacterial interaction studies, and shed new insights into how algicidal bacteria can be used in the control of harmful algal blooms, as well as in algal biotechnology.

Algicidal activity of a novel bacterium, Qipengyuania sp. 3-20A1M, against harmful Margalefidinium polykrikoides: Effects of its active compound

Margalefidinium polykrikoides causes significant economic losses in the aquaculture industry by red tide formation. Algicidal bacteria have attracted research interests as a potential bloom control approach without secondary pollution. Qipengyuania sp. 3-20A1M, isolated from surface seawater, exerted an algicidal effect on M. polykrikoides. However, it exhibited a significantly lower algicidal activity toward other microalgae. It reduced photosynthetic efficiency of M. polykrikoides and induced lipid peroxidation and cell disruption. The growth inhibition of M. polykrikoides reached 64.9 % after 24 h of co-culturing, and expression of photosynthesis-related genes was suppressed. It killed M. polykrikoides indirectly by secreting algicidal compounds. The algicide was purified and identified as pyrrole-2-carboxylic acid. After 24 h of treatment with pyrrole-2-carboxylic acid (20 μg/mL), 60.8 % of the M. polykrikoides cells were destroyed. Overall, our results demonstrated the potential utility of Qipengyuania sp. 3-20A1M and its algicidal compound in controlling M. polykrikoides blooms in the marine ecosystem.

Diflubenzuron Induces Cardiotoxicity in Zebrafish Embryos

Diflubenzuron is an insecticide that serves as a chitin inhibitor to restrict the growth of many harmful larvae, including mosquito larvae, cotton bollworm and flies. The residue of diflubenzuron is often detected in aquaculture, but its potential toxicity to aquatic organisms is still obscure. In this study, zebrafish embryos (from 6 h to 96 h post-fertilization, hpf) were exposed to different concentrations of diflubenzuron (0, 0.5, 1.5, 2.5, 3.5 and 4.5 mg/L), and the morphologic changes, mortality rate, hatchability rate and average heart rate were calculated. Diflubenzuron exposure increased the distance between the venous sinus and bulbar artery (SV-BA), inhibited proliferation of myocardial cells and damaged vascular development. In addition, diflubenzuron exposure also induced contents of reactive oxygen species (ROS) and malondialdehyde (MDA) and inhibited the activity of antioxidants, including SOD (superoxide dismutase) and CAT (catalase). Moreover, acridine orange (AO) staining showed that diflubenzuron exposure increased the apoptotic cells in the heart. Q-PCR also indicated that diflubenzuron exposure promoted the expression of apoptosis-related genes (bax, bcl2, p53, caspase3 and caspase9). However, the expression of some heart-related genes were inhibited. The oxidative stress-induced apoptosis damaged the cardiac development of zebrafish embryos. Therefore, diflubenzuron exposure induced severe cardiotoxicity in zebrafish embryos. The results contribute to a more comprehensive understanding of the safety use of diflubenzuron.

Functional role of a novel algicidal compound produced by Pseudoruegeria sp. M32A2M on the harmful algae Alexandrium catenella

A marine phytoplankton dinoflagellate, Alexandrium sp. is known to cause worldwide harmful algal blooms, resulting in paralytic shellfish poisoning. In this study, we isolated a novel compound secreted by the marine bacterium Pseudoruegeria sp. M32A2M, and showed that it displays algicidal activity against A. catenella (group I). The molecular structure of the compound was analyzed by using ¹H nuclear magnetic resonance (NMR), ¹³C NMR, and gas chromatography-mass spectrometry, which revealed that the compound was a diketopiperazine, cyclo[Ala-Gly]. Cyclo[Ala-Gly] induced a rapid decrease in the active chlorophyll a content and maximal quantum yield of photosystem II, leading to membrane disintegration after 24 h of its treatment. It showed the highest algicidal effect against diketopiperazines and also showed specific algicidal activities against several dinoflagellate species, but not for diatom species. In particular, cyclo[Ala-Gly] caused the transcriptional downregulation of the photosynthesis-related membrane complex in A. catenella, but not in the diatom Chaetoceros simplex. Based on structural modeling, we elucidated that cyclo[Ala-Gly] has a structure similar to that of plastoquinone, which transfers electrons by binding to the photosystem II core proteins PsbA and PsbD. This suggests a novel role for cyclo[Ala-Gly] as a potential inhibitor of photosynthesis.

Comparison of the toxic effects of non-task-specific and task-specific ionic liquids on zebrafish

Ionic liquids (ILs) are composed of only anions and cations and are liquid solvents at room temperature. Different functional groups were introduced into the ILs, conferring them with specific functions or purposes and thus forming special ILs, namely task-specific ILs (TSILs). Imidazolium-based ILs are the most widely used ILs in industrial production. To date, there have been some studies on the toxic effects of ILs on different organisms. However, the effect of functionalized groups on the toxicity of ILs is still unclear. In the present study, zebrafish were used as model organisms to study the toxic effects of 1-ethyl-3-methylimidazolium nitrate ([C₂mim]NO₃) and 1-hydroxyethyl-3-methylimidazolium nitrate ([HOC₂mim]NO₃). The results showed that both promoted an increase in reactive oxygen species (ROS) contents, leading to lipid peroxidation and DNA damage. Furthermore, integrated biological response analysis showed that [HOC₂mim]NO₃ was less toxic to zebrafish than [C₂mim]NO₃, which indicated that adding functional groups decreased the toxicity of ILs to organisms. The influence of chemical structure on IL toxicity was also reported. These results could provide a scientific basis for better synthesis and utilization of ILs in the future.

Algicidal Bacteria: A Review of Current Knowledge and Applications to Control Harmful Algal Blooms

Interactions between bacteria and phytoplankton in aqueous ecosystems are both complex and dynamic, with associations that range from mutualism to parasitism. This review focuses on algicidal interactions, in which bacteria are capable of controlling algal growth through physical association or the production of algicidal compounds. While there is some evidence for bacterial control of algal growth in the field, our understanding of these interactions is largely based on laboratory culture experiments. Here, the range of these algicidal interactions is discussed, including specificity of bacterial control, mechanisms for activity, and insights into the chemical and biochemical analysis of these interactions. The development of algicidal bacteria or compounds derived from bacteria for control of harmful algal blooms is reviewed with a focus on environmentally friendly or sustainable methods of application. Potential avenues for future research and further development and application of bacterial algicides for the control of algal blooms are presented.

Metabolomic Insights of the Effects of Bacterial Algicide IRI-160AA on Dinoflagellate Karlodinium veneficum

Shewanella sp. IRI-160 is an algicidal bacterium that secretes an algicide, IRI-160AA. This algicide specifically targets dinoflagellates, while having no adverse effects on other algal species tested. Dinoflagellates exposed to IRI-160AA exhibited increased production of reactive oxygen species (ROS), DNA damage, and cell cycle arrest, implying a programmed pathway leading to cell death (PCD). Here, a metabolomic analysis was conducted on dinoflagellate Karlodinium veneficum and a control cryptophyte species Rhodomonas exposed to IRI-160AA to investigate the cellular mechanisms behind the physiological effects and the specificity of this algicide. Results of this research supported previous observations about physiological responses to the algicide. A suite of metabolites was identified that increased in the cell pellets of K. veneficum but not in Rhodomonas, including oxidative stress biomarkers, antioxidants, and compounds involved in DNA damage and PCD. Overall, the results of this study illustrated the metabolomic mechanisms underlying the algicidal effects of IRI-160AA on dinoflagellates. This research also provided insights and future directions for studies on the cellular response of dinoflagellates exposed to antagonistic bacteria in the environment.

The potential of prodigiosin for control of Prorocentrum donghaiense blooms: Algicidal properties and acute toxicity to other marine organisms at various trophic levels

Prorocentrum donghaiense, a marine dinoflagellate, causes harmful algal blooms (HABs) characterised by the highest outbreak frequency and most extensive coverage among similar species in the East China Sea. Highly efficient and ecofriendly biocontrol strategies should be developed for HAB control. Prodigiosin is an efficient biological algicide that demonstrated strong algicidal activity towards P. donghaiense. However, the mechanism of its toxicity to P. donghaiense is unknown. These factors were investigated to evaluate potential use of prodigiosin for control of P. donghaiense blooms. Photosynthetic electron transport rate, maximum quantum yield and respiration rate of P. donghaiense decreased significantly upon exposure to prodigiosin, indicating that prodigiosin rapidly exerted adverse effects on the chloroplasts and mitochondria. Furthermore, a significant increase in dichlorofluorescein fluorescence intensity indicated an overproduction of reactive oxygen species (ROS). The antioxidant system of P. donghaiense scavenged ROS; however, an increase in malondialdehyde concentrations indicated that excessive ROS were still able to initiate lipid peroxidation. Thus, ROS production resulted in the formation of lipids with a reduced degree of unsaturation. Lipid peroxidation decreased lipid fluidity and rigidified the membrane system, causing serious functional destruction of the membrane. Flow cytometry analysis indicated that prodigiosin arrested the cell cycle of P. donghaiense. However, surviving algal cells were able to repair the damaged functions and resume the cell cycle after prodigiosin was removed by photodegradation. Otherwise, P. donghaiense cells lost their membrane integrity and died. To begin an evaluation of ecological safety of prodigiosin, we tested four marine organisms at various trophic levels. The results of these tests indicated that Chlorella vulgaris, Photobacterium phosphoreum, Artemia salina and Lateolabrax japonicus were less sensitive to prodigiosin than P. donghaiense. Toxicity to all five organisms declined after prodigiosin was exposed to sunlight for 6 h. Considering the toxic doses of prodigiosin to various organisms and its photodegradation characteristics, we suggest that prodigiosin has potential in controlling P. donghaiense blooms but should be applied at night, in small doses, with multiple applications.

Effects of allelochemical artemisinin in Artemisia annua on Microcystis aeruginosa: growth, death mode, and microcystin-LR changes

To investigate the effects of an allelochemical artemisinin extracted from Artemisia annua (A. annua) on cell growth, death mode, and microcystin-LR (MC-LR) changes of Microcystis aeruginosa (M. aeruginosa), a series of morphological and biochemical characteristics were studied. The results showed that artemisinin could inhibit the growth of M. aeruginosa and reduce the content of phycobiliprotein. Under the allelopathy of artemisinin, algae cells deformed due to swelling, which caused cell membranes to rupture and cell contents to leak. FDA/PI double-staining results showed that 15.10-94.90% of algae cells experienced the death mode of necrosis-like. Moreover, there were 8.35-14.50% of algae cells undergoing programmed cell death, but their caspase-3-like protease activity remained unchanged, which may mean that algae cells were not experiencing caspase-dependent apoptosis under artemisinin stress. Attacked by artemisinin directly, both intracellular and extracellular MC-LR increased sharply with the upregulation of mcyB, mcyD, and mcyH. The upregulation multiple of mcyH suggested that M. aeruginosa could accelerate transportation of algal toxin under adverse conditions of artemisinin. Artemisinin not only can inhibit the growth of M. aeruginosa but it also causes the accelerated release and increase of microcystin-LR. These imply that the application of artemisinin should be reconsidered in practical water bodies.

Killing effect of deinoxanthins on cyanobloom-forming Microcystis aeruginosa: Eco-friendly production and specific activity of deinoxanthins

Cyanobacterial blooms caused mainly by Microcystis aeruginosa could be controlled using chemical and biological agents such as H₂O₂, antagonistic bacteria, and enzymes. Little is known about the possible toxic effects of bacterial membrane pigments on M. aeruginosa cells. Deinococcus metallilatus MA1002 cultured under light increased the production of several carotenoid-like compounds by upregulating two deinoxanthin biosynthesis genes: crtO and cruC. The deinoxanthin compounds were identified using thin-layer chromatography, high-performance liquid chromatography, and liquid chromatography-mass spectrometry. D. metallilatus was cultured with agricultural by-products under light to produce the deinoxanthin compounds. Soybean meal, from six tested agricultural by-products, was selected as the single factor for making an economical medium to produce deinoxanthin compounds. The growth of axenic M. aeruginosa PCC7806, as well as other xenic cyanobacteria such as Cyanobium gracile, Trichormus variabilis, and Dolichospermum circinale, were inhibited by the deinoxanthin compounds. Scanning electron microscopic images showed the complete collapse of M. aeruginosa cells under deinoxanthin treatment, probably due to its interference with cyanobacterial membrane synthesis during cellular elongation. Deinoxanthins appeared to be nontoxic to other non-cyanobacteria such as Acinetobacter, Pseudomonas, Methylobacterium, and Bacillus species, suggesting that it can be a novel candidate for preventing cyanobacterial blooms through its specific activity against cyanobacteria.

Algicidal activity of a novel indigenous bacterial strain of Paracoccus homiensis against the harmful algal bloom species, Karenia mikimotoi

Harmful algal blooms have deleterious effects on aquatic ecosystems and human health. The application of algicidal bacteria is a promising and environmentally friendly method of preventing and eradicating harmful algal blooms. In this study, a screen for algicidal agents against harmful algal blooms was used to identify an algicidal bacterial strain (strain O-4) isolated from a Karenia mikimotoi culture. Strain O-4 exhibited a strong inhibitory effect on harmful K. mikimotoi and was identified as Paracoccus homiensis via 16S rRNA gene sequence analysis. This strain killed K. mikimotoi by secreting active algicidal compounds, which were stable at temperatures of -80-121 °C but were sensitive to strongly acidic conditions (pH = 2). The algicidal properties of strain O-4 against K. mikimotoi were cell density- and time-dependent. No significant changes or negative effects were noted for two other Chlorophyta species, which highlighted the specificity of the studied algicidal substance. Finally, single-factor experiments revealed the optimum growth conditions of strain O-4 under different pH and temperature conditions. Therefore, strain O-4 has the potential to be used as a bio-agent for reducing the biomass of harmful K. mikimotoi blooms.

Study of the properties of carotenoids and key carotenoid biosynthesis genes from Deinococcus xibeiensis R13

To investigate the properties of carotenoids from the extremophile Deinococcus xibeiensis R13, the factors affecting the stability of carotenoids extracted from D. xibeiensis R13, including temperature, illumination, pH, redox chemicals, metal ions, and food additives, were investigated. The results showed that low temperature, neutral pH, reducing agents, Mn²⁺ , and food additives (xylose and glucose) can effectively improve the stability of Deinococcus carotenoids. The carotenoids of D. xibeiensis R13 exhibited strong antioxidant activity, with the scavenging rate of hydroxyl radicals reaching 71.64%, which was higher than the scavenging efficiency for 1,1-diphenyl-2-picrylhydrazyl free radicals and 2,2'-azino-bis (3-ethyl-benzothiazoline-6-sulfonic acid) free radicals (44.55 and 27.65%, respectively). In addition, the total antioxidant capacity reached 0.60 U/ml, which was 2.61-fold that of carotenoids from the model strain Deinococcus radiodurans R1. Finally, we predicted the gene clusters encoding carotenoid biosynthesis pathways in the genome of R13 and identified putative homologous genes. The key enzyme genes (crtE, crtB, crtI, crtLm, cruF, crtD, and crtO) in carotenoid synthesis of D. xibeiensis R13 were cloned to construct the multigene coexpression plasmids pET-EBI and pRSF-LmFDO. The carotenoid biosynthesis pathway was heterologously introduced into engineered Escherichia coli EBILmFDO, which exhibited a higher yield (7.14 mg/L) than the original strain. These analysis results can help us to better understand the metabolic synthesis of carotenoids in extremophiles.

Bacteria enhance the production of extracellular polymeric substances by the green dinoflagellate Lepidodinium chlorophorum

High biomasses of the marine dinoflagellate Lepidodinium chlorophorum cause green seawater discolorations along Southern Brittany (NE Atlantic, France). The viscosity associated to these phenomena has been related to problems in oyster cultivation. The harmful effect of L. chlorophorum might originate from the secretion of Extracellular Polymeric Substances (EPS). To understand whether the EPS are produced by L. chlorophorum or its associated bacteria, or if they are a product of their interaction, batch cultures were performed under non-axenic and pseudo-axenic conditions for three strains. Maximum dinoflagellate cell abundances were observed in pseudo-axenic cultures. The non-sinking fraction of polymers (Soluble Extracellular Polymers, SEP), mainly composed of proteins and the exopolysaccharide sulphated galactan, slightly increased in pseudo-axenic cultures. The amount of Transparent Exopolymer Particles (TEP) per cell increased under non-axenic conditions. Despite the high concentrations of Particulate Organic Carbon (POC) measured, viscosity did not vary. These results suggest that the L. chlorophorum-bacteria interaction could have a detrimental consequence on the dinoflagellate, translating in a negative effect on L. chlorophorum growth, as well as EPS overproduction by the dinoflagellate, at concentrations that should not affect seawater viscosity.

Emerging contaminant 1,3,6,8-tetrabromocarbazole induces oxidative damage and apoptosis during the embryonic development of zebrafish (Danio rerio)

Since polyhalogenated carbazoles (PHCs) have been widely detected at high concentrations in multiple environmental media in recent years, the health risk of exposure to these compounds has drawn increasing attention. Most studies have mainly focused on their dioxin-like toxicity, which is induced through the AhR pathway, because PHCs have structures similar to those of polychlorinated dibenzofurans (PCDFs). In addition, most xenobiotic compounds induce oxidative stress in organisms, which is a more common mechanism of toxicity induction. However, there is limited information regarding the oxidative stress and damage induced by PHCs in vivo. The PHC 1,3,6,8-tetrabromocarbazole (1368-TBCZ) is detected at high concentration and frequency. In the present study, the toxic effects (acute toxicity, developmental toxicity, oxidative stress, and apoptosis) induced by 1368-TBCZ at three different concentrations were investigated using zebrafish embryos. It was concluded that the 96 h median lethal concentration (LC₅₀) of 1368-TBCZ for zebrafish embryos was greater than 2.0 mg L^-1. The results showed that 1368-TBCZ had little effect on the hatching rate of zebrafish embryos. However, 1368-TBCZ at 0.5 and 2.0 mg L^-1 inhibited skeletal and cardiac development. It promoted ROS production, CAT enzyme activity, lipid peroxidation, DNA damage, and apoptosis, even at the lowest dose (0.1 mg L^-1). In addition, 1368-TBCZ influenced oxidative stress-related gene expression, upregulating the expression of caspase 3 and p53 at 2.0 mg L^-1 and inhibiting the expression of caspase 9, FoxO3b, and Bcl-2/Bax. The present study comprehensively evaluated 1368-TBCZ-induced toxicity in zebrafish, providing valuable data for better evaluation of the potential risks posed by this PHC.

Harmful Cyanobacterial Blooms (HCBs): innovative green bioremediation process based on anti-cyanobacteria bioactive natural products

Over the last decades, Harmful Cyanobacterial Blooms (HCBs) represent one of the most conspicuous hazards to human health in freshwater ecosystems, due to the uses of the water for drinking, recreation and aquaculture. Cyanobacteria are one of the main biological components in freshwater ecosystems and they may proliferate in nutrients rich ecosystems causing severe impacts at different levels. Therefore, several methods have been applied to control cyanobacterial proliferation, including physical, chemical and biological strategies. However, the application of those methods is generally not very efficient. Research on an eco-friendly alternative leading to the isolation of new bioactive compounds with strong impacts against harmful cyanobacteria is a need in the field of water environment protection. Thus, this paper aims to give an overview of harmful cyanobacterial blooms and reviews the state of the art of studying the activities of biological compounds obtained from plants, seaweeds and microorganisms in the cyanobacterial bloom control.

Effects of pH and nitrogen form on Nitzschia closterium growth by linking dynamic with enzyme activity

In this study, Nitzschia closterium was incubated in seawater at different pH values (8.10, 7.71, and 7.45) and using different nitrogen forms (NO₃-N and NH₄-N) in the laboratory. The results showed that the growth of N. closterium was inhibited by ocean acidification, with individuals under lower pH levels showing lower growth rates and lower nitrogen uptake rates for both nitrogen forms. The V_max/K_s ratio decreased with decreasing pH, indicating the inhibition of nitrogen uptake, whereas the ratios for NH₄-N cultures were higher than those for NO₃-N cultures, implying the highly competitive position of NH₄-N. Acidification might induce reactive oxygen species based on the result that the maximum enzyme activities of SuperOxide Dismutase (SOD) and CATalase (CAT) increased under lower pH levels. The SOD and CAT activities for the NO₃-N cultures were higher than those for NH₄-N cultures at the low pH level, indicating that acidification might cause more oxidative stress for NO₃-N cultures than for NH₄-N cultures. Thus, ocean acidification might have a more detrimental effect on the growth of N. closterium under NO₃-N conditions than NH₄-N conditions, with a lower ratio (γ) of the maximum growth rate to the maximum nutrient uptake rate, and a drop in nitrate reductase activity under lower pH levels.

Immobilization of algicidal bacterium Shewanella sp. IRI-160 and its application to control harmful dinoflagellates

Shewanella sp. IRI-160 is an algicidal bacterium isolated from Delaware Inland Bays. It secretes water-soluble compounds that inhibit the growth of dinoflagellates. Previous research indicated that this bacterium does not have a negative impact on other algal species. In this research, Shewanella sp. IRI-160 was immobilized to different porous matrices, including agarose, alginate hydrogel, cellulosic sponge, and polyester foam. The retention of Shewanella sp. IRI-160 on or within these matrices was examined at 4 and 25 °C for 12 days. Results indicated that alginate was superior in terms of cell retention, with >99% of Shewanella cells retained in the matrix after 12 days. Shewanella sp. IRI-160 cells were then immobilized within alginate beads to evaluate algicidal effects on harmful dinoflagellates Karlodinium veneficum and Prorocentrum minimum at bacterial concentrations of 10⁶ to 10⁸ cells mL^-1. The effects on dinoflagellates were compared to non-harmful cryptophyte Rhodomonas sp., as well as the effects of free-living bacteria on these species. Results indicated that immobilized Shewanella sp. IRI-160 in alginate beads were as effective as the free-living bacteria to control the growth of K. veneficum and P. minimum, while no negative impacts of immobilized Shewanella sp. IRI-160 on the non-harmful control species Rhodomonas sp. were observed. Overall, this study suggests that immobilized Shewanella sp. IRI-160 may be used as an environmentally friendly approach to prevent or mitigate the blooms of harmful dinoflagellates and provides insight and directions for future studies.

Simultaneous Microcystis algicidal and microcystin synthesis inhibition by a red pigment prodigiosin

Microcystis blooms and their secondary metabolites microcystins (MCs) occurred all over the world, which have damaged aquatic ecosystems and threatened public health. Techniques to reduce the Microcystis blooms and MCs are urgently needed. This study aimed to investigate the algicidal and inhibitory mechanisms of a red pigment prodigiosin (PG) against the growth and MC-producing abilities of Microcystis aeruginosa (M. aeruginosa). The numbers of Microcystis cells were counted under microscope. The expression of microcystin synthase B gene (mcyB) and concentrations of MCs were determined by quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme linked immunosorbent assay (ELISA) methods, respectively. The inhibitory effects of PG against M. aeruginosa strain FACHB 905 with 50% algicidal concentration (LC₅₀) at 120 h was 0.12 μg/mL. When M. aeruginosa cells exposed to 0.08 μg/mL, 0.16 μg/mL, 0.32 μg/mL PG, the expression of mcyB of M. aeruginosa was down-regulated 4.36, 8.16 and 18.51 times lower than that of the control at 120 h. The concentrations of total MC (TMC) also were 1.66, 1.72 and 5.75 times lower than that of the control at 120 h. PG had high algicidal effects against M. aeruginosa, with the activities of superoxide dismutase (SOD) initially increased and then decreased after 72 h, the contents of malondialdehyde (MDA) increase, the expression of mcyB gene down-regulation, and MCs synthesis inhibition. This study was first to report the PG can simultaneously lyse Microcystis cells, down-regulate of mcyB expression and inhibit MCs production effectively probably due to oxidative stress, which indicated PG poses a great potential for regulating Microcystis blooms and MCs pollution in the environment.

Effects of carbon source, nitrogen source, and natural algal powder-derived carbon source on biodegradation of tetracycline (TEC)

The present study aimed to investigate Klebsiella sp. SQY5-mediated tetracycline (TEC) degradation, nitrogen (N) conversion, and mechanisms underlying this process as influenced by various carbon and N sources under aerobic conditions. Effects of additional organic carbon sources on TEC degradation and N conversion processes were explored, and we found that 34.71% of TEC was degraded at removal rates of 0.97 mg·L^-1·h^-1 for NH₄⁺-N and 1.97 mg·L^-1·h^-1 for NO₃^--N. A study examining powder natural algal powder in aquaculture wastewater as a carbon source for TEC degradation and denitrification process was also discussed. It suggested that 49.95% of TEC and 60.45% of NO₃^--N were removed with a reduction and denitrification rate of 0.11 mg·L^-1·h^-1 and 1.34 mg·L^-1·h^-1, respectively, within 72-108 h. Mechanisms underlying TEC degradation and N conversion processes were also proposed, and analysis indicated that specific functional genes played an important role in this process.

Ecological risk assessment of alpha-cypermethrin-treated food ingestion and reproductive toxicity in reptiles

Pesticides are proposed as one of the many causes for the global decline in reptile population. To understand the potential impact of alpha-cypermethrin (ACP) in reptiles, in the current study, we used a tri-trophic food web (plants - herbivores - natural enemies of predators) to examine the reproductive toxicity and biomarker changes. Based on the Maximum Residue Limit (MRL) of ACP in several agricultural products, we designed three concentrations 0, 2 (MRL), and 20 mg/kg _{wet weight} as three treatment groups for this research. Male and female lizards were fed ACP contaminated or uncontaminated diets for eight weeks during the breeding phase. The number of deaths was different among the three groups, and a dose-dependent trend was found. Decreases in food consumption of 26.6% and 28.1% were observed in the low- and high-dose group, respectively. Dietary exposure significantly induced a dose-dependent decrease in body mass index in lizards. Significant variations in glutathione-S-transferaseb activities, catalase activities, and malondialdehyde levels in gonads, suggest that lizards were under oxidative stress. In addition, ACP exposure altered sexual hormone levels in males, reduced reproductive output of females, and induced histopathological changes in testes. These negative effects highlight that ACP dietary exposure is a potential threat to lizards' reproduction.

Ulva prolifera green-tide outbreaks and their environmental impact in the Yellow Sea, China

The Ulva prolifera green tides in the Yellow Sea, China, which have been occurring since 2007, are a serious environmental problem attracting worldwide attention. Despite extensive research, the outbreak mechanisms have not been fully understood. Comprehensive analysis of anthropogenic and natural biotic and abiotic factors reveals that human activities, regional physicochemical conditions and algal physiological characteristics as well as ocean warming and biological interactions (with microorganism or other macroalgae) are closely related to the occurrence of green tides. Dynamics of these factors and their interactions could explain why green tides suddenly occurred in 2007 and decreased abruptly in 2017. Moreover, the consequence of green tides is serious. The decay of macroalgal biomass could result in hypoxia and acidification, possibly induce red tide and even have a long-lasting impact on coastal carbon cycles and the ecosystem. Accordingly, corresponding countermeasures have been proposed in our study for future reference in ecosystem management strategies and sustainable development policy.

Algicidal Activity of Novel Marine Bacterium Paracoccus sp. Strain Y42 against a Harmful Algal-Bloom-Causing Dinoflagellate, Prorocentrum donghaiense

Prorocentrum donghaiense blooms occur frequently in the Yangtze River estuary and the adjacent East China Sea. These blooms have damaged marine ecosystems and caused enormous economic losses over the past 2 decades. Thus, highly efficient, low-cost, ecofriendly approaches must be developed to control P. donghaiense blooms. In this study, a bacterial strain (strain Y42) was identified as Paracoccus sp. and was used to lyse P. donghaiense The supernatant of the strain Y42 culture was able to lyse P. donghaiense, and the algicidal activity of this Y42 supernatant was stable with different temperatures and durations of light exposure and over a wide pH range. In addition to P. donghaiense, Y42 showed high algicidal activity against Alexandrium minutum, Scrippsiella trochoidea, and Skeletonema costatum, suggesting that it targets primarily Pyrrophyta. To clarify the algicidal effects of Y42, we assessed algal lysis and determined the chlorophyll a contents, photosynthetic activity, and malondialdehyde contents of P. donghaiense after exposure to the Y42 supernatant. Scanning electron microscopy and transmission electron microscopy analyses showed that the Y42 supernatant disrupted membrane integrity and caused algal cell breakage at the megacytic zone. Photosynthetic pigment loss and significant declines in both photosynthetic efficiency and the electron transport rate indicated that the Y42 supernatant damaged the photosynthetic system of P. donghaiense Malondialdehyde overproduction indicated that the Y42 supernatant caused lipid peroxidation and oxidative damage to membrane systems in the algal cell, ultimately leading to death. The findings of this study reveal the potential of Y42 to remove algal cells from P. donghaiense blooms.IMPORTANCEP. donghaiense is one of the most common dinoflagellate species that form harmful algal blooms, which frequently cause serious ecological pollution and pose health hazards to humans and other animals. Screening for bacteria with high algicidal activity against P. donghaiense and studying their algicidal processes and characteristics will contribute to an understanding of their algicidal effects and provide a theoretical basis for preventing algal blooms and reducing their harm to the environment. This study reports the algicidal activity and characteristics of Paracoccus against P. donghaiense The stability of the algicidal activity of Paracoccus in different environments (including different temperature, pH, and sunlight conditions) indicates its potential for use in the control of P. donghaiense blooms.

The effects of a water-soluble alpha tetra-substituted zinc phthalocyanine derivative onArthrospira platensis-M2 strain

In this study, we have analyzed the effect a newly synthesized water-soluble alpha tetra-substituted zinc phthalocyanine (Pc) compound on superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) activities and biomass accumulation in the Arthrospira platensis-M2 strain to test whether this compound could be used as an algaecide or not. We found that lower concentrations (3 μg mL[Formula: see text] and 6 μg mL[Formula: see text] of Pc compound were not toxic to algae cells, as indicated by enduring biomass accumulation during the study (7 days). Higher Pc concentrations, however, were toxic and inhibited biomass accumulation. This inhibition appeared on the fourth day and persisted during the study. At higher Pc concentrations, SOD activity decreased significantly, but APX and GR activity were not affected. These results may show that Pc applications did not cause the accumulation of reactive oxygen species in Arthrospira platensis-M2 cells. Our result suggests that higher Pc concentrations did not cause oxidative stress but biomass accumulation inhibited, possibly due to some different toxicity mechanism(s), which should be carried out in the future studies. As a result, we may offer use of this compound as a means to keep under control algal populations in natural environments.

Strategies and ecological roles of algicidal bacteria

In both freshwater and marine ecosystems, phytoplankton are the most dominant primary producers, contributing substantially to aquatic food webs. Algicidal bacteria that can associate to microalgae from the phytoplankton have the capability to control the proliferation and even to lyse them. These bacteria thus play an important role in shaping species composition in pelagic environments. In this review, we discuss and categorise strategies used by algicidal bacteria for the attack on microalgae. We highlight the complex regulation of algicidal activity and defence responses that govern alga-bacteria interactions. We also discuss how algicidal bacteria impact algal physiology and metabolism and survey the existing algicidal metabolites and enzymes. The review illustrates that the ecological role of algicidal bacteria is not yet fully understood and critically discusses the challenges in obtaining ecologically relevant data.

Microorganisms-based methods for harmful algal blooms control: A review

Harmful algal blooms (HABs) are a worldwide problem with numerous negative effects on water systems, which have prompted researchers to study applicable measures to inhibit and control them. This review summarized the current microorganisms-based methods or technologies aimed at controlling HABs. Based on their characteristics, these methods can be divided into two categories: methods based on single-species microorganisms and methods based on microbial aggregates, and four types: methods for rapid decrease of algal cells density (e.g., alga-bacterium and alga-fungus bioflocculation), inhibition of harmful algal growth, lysis of harmful algae (e.g. algicidal bacteria, fungi, and actinomycete), and methods based on microbial aggregates (periphytons and biofilms). An integrative process of "flocculation-lysis-degradation-nutrients regulation" is proposed to control HABs. This review not only offers a systematic understanding of HABs control technologies based on microorganisms but also elicits a re-thinking of HABs control based on microbial aggregates.

The algicidal mechanism of prodigiosin from Hahella sp. KA22 against Microcystis aeruginosa

In recent years, Microcystis aeruginosa blooms have occurred throughout the world, causing huge economic losses and destroying aquatic ecosystems. It is necessary to develop effective and ecofriendly methods to control M. aeruginosa blooms. Here, we report a high algicidal activity of prodigiosin (PG) against M. aeruginosa as well as the algicidal mechanism. PG showed high algicidal activity against M. aeruginosa, with a 50% lethal dose (LD₅₀) of 5.87 μg/mL in 72 h. A combination of methods, including propidium iodide and Annexin V-fluorescein staining assays and light and electron microscopy indicated the existence of two modes of cell death with features similar to those in eukaryotic programmed cell death: necrotic-like and apoptotic-like. Biochemical and physiological analyses showed that PG generates reactive oxygen species (ROS), which induce lipid peroxidation, damage the membrane system and destroy the function of the photosystem. A proteomics analysis revealed that many proteins were differentially expressed in response to PG stress and that most of these proteins were involved in important metabolic processes, which may trigger necrotic-like or apoptotic-like cell death. The present study sheds light on the multiple toxicity mechanisms of PG on M. aeruginosa and its potential for controlling the occurrence of M. aeruginosa blooms in lakes.

A Bacillus sp. strain with antagonistic activity against Fusarium graminearum kills Microcystis aeruginosa selectively

Cyanobacterial harmful algal blooms (CyanoHABs) cause severe environmental problems, economic losses and threaten human health seriously. In the present study, a Bacillus sp. strain, designated as AF-1, with strong antagonistic activity against plant pathogenic fungus Fusarium graminearum was isolated from purple soil. Bacillus sp. AF-1 selectively killed Microcystis aeruginosa at low cell density (1.6×10³cfu/mL), and showed the strongest bactericidal activity against M. aeruginosa NIES-843 (A_e=93%, t=6d). The algicidal substances originated from strain AF-1 were stable in the temperature range of 35-100°C, and pH range of 3-11. Cell-free filtrate of AF-1 culture caused excessive accumulation of intracellular reactive oxygen species (ROS), cell death and the efflux of intracellular components of M. aeruginosa NIES-843 cells. The expression of genes recA, psbA1, psbD1, rbcL and mcyB, involved in DNA repair, photosynthesis and microcystin synthesis of NIES 843, were significantly influenced by the cell-free filtrate of AF-1 culture. Bacillus sp. AF-1 has the potential to be developed as a bifunctional biocontrol agent to control CyanoHABs and F. graminearum caused plant disease.

Stress of algicidal substances from a bacterium Exiguobacterium sp. h10 on Microcystis aeruginosa

Microcystis aeruginosa is a cyanobacterial bloom-causing species and is considered a serious threat to human health and biological safety. In this study, the algicidal bacterium h10 showed high algicidal effects on M. aeruginosa 7820, and strain h10 was confirmed to belong to the genus Exiguobacterium, for which the name Exiguobacterium sp. h10 is proposed. Algicidal activity and mode analysis revealed that the supernatant, rather than the bacterial cells, was responsible for the algicidal activity, indicating that the algicidal mode of strain h10 is by indirect attack through the production of algicidal substances. Analysis of the algicidal substance characteristics showed a molecular weight of <1000 Da and that algicidal substances exhibit high thermal stability and pH instability, and the characteristic functional groups of the algicidal substance mainly included carbonyl, amino and hydroxyl groups. Under the effects of the algicidal substance, the cellular pigment content was significantly decreased, and the algal cell structure and morphology were seriously damaged. The results indicate that the algicidal bacterium Exiguobacterium sp. h10 could be a potential bio-agent for controlling cyanobacterial blooms of M. aeruginosa.

SIGNIFICANCE AND IMPACT OF THE STUDY

In this study, the effects of algicidal substances from an algicidal bacterium Exiguobacterium sp. h10 on the toxic cyanobacterium, Microcystis aeruginosa 7820, were first investigated. The algicidal mode of action was confirmed as an indirect attack through the production of algicidal substances. The characteristics of the algicidal substance were determined, especially the functional groups analysis that confirmed the algicidal substances were glycolipid mixtures. With the stress of algicidal substances, the algal chlorophyll a synthesis, cell structure and morphology were seriously damaged. This study proved that algicidal bacteria are promising sources of potential cyanobacterial bloom-control, and provided good procedures for the identification and analysis of an algicidal bacterium and substances.

Simultaneous Microcystis Algicidal and Microcystin Degrading Capability by a Single Acinetobacter Bacterial Strain

Measures for removal of toxic harmful algal blooms often cause lysis of algal cells and release of microcystins (MCs). In this study, Acinetobacter sp. CMDB-2 that exhibits distinct algal lysing activity and MCs degradation capability was isolated. The physiological response and morphological characteristics of toxin-producing Microcystis aeruginosa, the dynamics of intra- and extracellular MC-LR concentration were studied in an algal/bacterial cocultured system. The results demonstrated that Acinetobacter sp. CMDB-2 caused thorough decomposition of algal cells and impairment of photosynthesis within 24 h. Enhanced algal lysis and MC-LR release appeared with increasing bacterial density from 1 × 10³ to 1 × 10⁷ cells/mL; however, the MC-LR was reduced by nearly 94% within 14 h irrespective of bacterial density. Measurement of extracellular and intracellular MC-LR revealed that the toxin was decreased by 92% in bacterial cell incubated systems relative to control and bacterial cell-free filtrate systems. The results confirmed that the bacterial metabolite caused 92% lysis of Microcystis aeruginosa cells, whereas the bacterial cells were responsible for approximately 91% reduction of MC-LR. The joint efforts of the bacterium and its metabolite accomplished the sustainable removal of algae and MC-LR. This is the first report of a single bacterial strain that achieves these dual actions.

First evidence of bioflocculant from Shinella albus with flocculation activity on harvesting of Chlorella vulgaris biomass

Bioflocculant from Shinella albus xn-1 could be used to harvest energy-producing microalga Chlorella vulgaris biomass for the first time. In this study, we investigated the flocculation activity and mode of strain xn-1, the characteristics of bioflocculant, the effect of flocculation conditions and optimized the flocculation efficiency. The results indicated that strain xn-1 exhibited flocculation activity through secreting bioflocculant; the bioflocculant with high thermal stability, pH stability and low molecular weight was proved to be not protein and polysaccharide, and flocculation active component was confirmed to contain triple bond and cumulated double bonds; algal pH, temperature and metal ions showed great impacts on the flocculation efficiency of bioflocculant; the maximum flocculation activity of bioflocculant reached 85.65% after the response surface optimization. According to the results, the bioflocculant from S. albus xn-1 could be a good potential in applications for high-efficiency harvesting of microalgae.

The S-layer Protein DR_2577 Binds Deinoxanthin and under Desiccation Conditions Protects against UV-Radiation in Deinococcus radiodurans

Deinococcus radiodurans has the puzzling ability to withstand over a broad range of extreme conditions including high doses of ultraviolet radiation and deep desiccation. This bacterium is surrounded by a surface layer (S-layer) built of a regular repetition of several proteins, assembled to form a paracrystalline structure. Here we report that the deletion of a main constituent of this S-layer, the gene DR_2577, causes a decrease in the UVC resistance, especially in desiccated cells. Moreover, we show that the DR_2577 protein binds the carotenoid deinoxanthin, a strong protective antioxidant specific of this bacterium. A further spectroscopical characterization of the deinoxanthin-DR_2577 complex revealed features which could suggest a protective role of DR_2577. We propose that, especially under desiccation, the S-layer shields the bacterium from incident ultraviolet light and could behave as a first lane of defense against UV radiation.

The death mechanism of the harmful algal bloom species Alexandrium tamarense induced by algicidal bacterium Deinococcus sp. Y35

Harmful algal blooms (HABs) cause a variety of deleterious effects on aquatic ecosystems, especially the toxic dinoflagellate Alexandrium tamarense, which poses a serious threat to marine economic and human health based on releasing paralytic shellfish poison into the environment. The algicidal bacterium Deinococcus sp. Y35 which can induce growth inhibition on A. tamarense was used to investigate the functional mechanism. The growth status, reactive oxygen species (ROS) content, photosynthetic system and the nuclear system of algal cells were determined under algicidal activity. A culture of strain Y35 not only induced overproduction of ROS in algal cells within only 0.5 h of treatment, also decrease the total protein content as well as the response of the antioxidant enzyme. Meanwhile, lipid peroxidation was induced and cell membrane integrity was lost. Photosynthetic pigments including chlorophyll a and carotenoid decreased along with the photosynthetic efficiency being significantly inhibited. At the same time, photosynthesis-related gene expression showed down-regulation. More than, the destruction of cell nuclear structure and inhibition of proliferating cell nuclear antigen (PCNA) related gene expression were confirmed. The potential functional mechanism of the algicidal bacterium on A. tamarense was investigated and provided a novel viewpoint which could be used in HABs control.