Algicidal characterization and mechanism of Bacillus licheniformis Sp34 against Microcystis aeruginosa in Dianchi Lake

Influence of bloom stage on the effectiveness of algicidal bacteria in controlling harmful cyanobacteria: A microcosm study

Cyanobacterial harmful algae blooms (cyanoHABs) pose significant ecological and public health concerns in freshwater ecosystems worldwide. Understanding the dynamics of phytoplankton communities and the efficacy of mitigation strategies is crucial for managing bloom events. This study investigates the impact of bioaugmentation with algicidal bacteria on Microcystis-dominated blooms through laboratory microcosm experiments. Field-collected samples from MID- and POST-summer bloom stages were treated with Morganella morganii, Exiguobacterium acetylicum, and a bacterial consortium including Bacillus pumilus. Phytoplankton composition, microcystin concentrations and genes related to microbial community dynamics (16S, mcyA, nosZ and amoA) were assessed by microscopy, HPLC and qPCR, respectively. Results showed that M. morganii significantly altered the phytoplankton community structure and promoted diatom proliferation in MID-summer microcosms, though treatments were less effective in POST-summer microcosms representing more mature bloom periods. Additionally, algicidal bacteria influenced microcystin levels, with M. morganii and E. acetylicum reducing toxigenic Microcystis genotypes, as indicated by lower mcyA gene copy numbers. Molecular analyses also revealed that algicidal bacterial treatments contributed to shifts in microbial functional genes, including increased denitrification activity linked to nosZ gene abundance. These findings highlight the intricate interplay between algicidal bacteria and microbial communities, where algicidal activity extends beyond direct cyanobacteria suppression to broader ecosystem-level effects. By rebalancing phytoplankton communities toward eukaryotic dominance and reducing toxigenic cyanobacterial genotypes during intense bloom episodes, bioaugmentation with algicidal bacteria emerges as a promising strategy for bloom management and ecosystem restoration.

New Pyridinium Compound from Marine Sediment-Derived Bacterium Bacillus licheniformis S-1

The structural diversity of marine natural products is considered a potential resource for the pharmaceutical industry. In our study of marine-derived compounds, one bacterium Bacillus licheniformis S-1 was discovered to have the ability to produce bioactive natural products. After a further chemistry investigation, one novel 4-aminopyridinium derivative, 4-(dimethylamino)-1-(2S-((4hydroxybenzoyl)oxy)propyl)pyridin-1-ium (1), along with 15 known cyclic dipeptides (2-16) were isolated from the bacterium B. licheniformis S-1 derived from a shallow sea sediment. The structures of compounds 1-16 were elucidated through comprehensive NMR spectroscopic and specific optical rotation (OR) data analyses. Compound 6 showed antibacterial activity against Pseudomonas fulva with an MIC value of 50 µg/mL. This is the first study to discover a pyridinium derivative and cyclic dipeptides from B. licheniformis.

Per- and polyfluoroalkyl substances (PFAS) at low concentration improve coagulation efficiency but induce higher membrane fouling in drinking water treatment

The presence of per- and polyfluoroalkyl substances (PFAS) in surface water has been widely reported in recent years. Many techniques, e.g., adsorption, have been investigated to remove PFAS from contaminated waters. However, the underlying impacts of PFAS on conventional drinking water treatment have been overlooked so far. In this study, we hypothesized whether PFAS have significant impacts on algae in surface water, which in turn may influence the performance of typical treatment processes (e.g., coagulation/membrane filtration). Therefore, we sampled a representative surface water (drinking water source) in Beijing, China, and dosed 2 representative PFAS compounds, at environment concentrations, to conduct bench-scale treatment tests. Results showed that the presence of PFAS caused larger flocs during coagulation and more severe ultrafiltration (UF) membrane fouling, compared with a control solution without PFAS. Specifically, PFAS at a low concentration (0.1 μg/L) led to the greatest influence on floc growth and UF membrane fouling; compared with the solution without PFAS, the floc size increased by 1.6 times and membrane flux declined more than 10%. These effects were evidenced by the stress response of algae under PFAS stimulus, secreting more biopolymers (mainly polysaccharides), rather than by PFAS directly. Overall, this study has demonstrated that the presence of PFAS can have both beneficial, and undesirable, indirect effects on water treatment in real applications, through its impact on algae in surface water sources.

A Bacillus subtilis strain with efficient algaecide of Microcystis aeruginosa and degradation of microcystins

Global concerns over harmful cyanobacterial blooms brought on by eutrophication are now widespread. Aquatic ecological restoration techniques that use algicidal bacteria to control toxic algae show promise. A Bacillus subtilis S4 (S4) strain with strong Microcystis aeruginosa algicidal activity and the capacity to degrade microcystins (MCs) were successfully isolated and evaluated in this study. The dynamics of internal and extracellular MC concentration as well as the physiological response and morphological properties of M. aeruginosa were investigated in the M. aeruginosa/bacteria co-culture system. The findings demonstrated that when S4 density grew from 1 × 106 cells/ml to 1 × 108 cells/ml, the release of M. aeruginosa lysis and MCs was boosted; however, MCs dropped by approximately 90% within 18 h, regardless of bacterial density. Comparing the bacterial cell incubation system to the control and bacterial cell-free filtrate systems, the assessment of extracellular and intracellular MCs revealed a 95% reduction in MCs. The findings showed that 89% of MCs were decreased by bacterial cells, while 98% of M. aeruginosa cells were algaecided by bacterial metabolites. Sustainable eradication of M. aeruginosa and MCs has been accomplished by the combined efforts of the S4 strain and its metabolites. By secreting algicidal chemicals that are resistant to proteases, acid, base, and heat, the S4 strain indirectly acts as an algaecide. The S4 strain possesses a strong ability to break down MCs and a very effective and stable algaecide function, indicating that it can potentially treat eutrophic water with hazardous algae.

Natural Antimicrobial Agents from Algae: Current Advances and Future Directions

Infectious diseases have significantly shaped human history, leading to significant advancements in medical science. The discovery and development of antibiotics represented a critical breakthrough, but the rise of antibiotic-resistant pathogens now presents a serious global health threat. Due to the limitations of current synthetic antimicrobials, such as toxicity and environmental concerns, it is essential to explore alternative solutions. Algae, particularly microalgae and cyanobacteria, have emerged as promising sources of bioactive antimicrobial compounds. This review provides a comprehensive analysis of the antimicrobial properties of algal-derived compounds, including polysaccharides, fatty acids, and phenols, which have shown effectiveness against multi-drug-resistant bacteria. A co-occurrence bibliometric analysis using VOSviewer highlighted five key research clusters: antibiotic resistance, algal extracts, biosynthesis, water treatment, and novel pharmacological compounds. Furthermore, the primary mechanisms of action of these bioactive compounds, such as the inhibition of protein synthesis and cell membrane disruption, were identified, demonstrating their potential against both common and multi-resistant pathogens. Future research should prioritize optimizing algal biomass production, utilizing genetic and metabolic engineering, and creating innovative delivery systems to enhance the efficient production of bioactive compounds.

Pseudomonas ZY-1 and Bacillus FY-1 protecting the rice seedlings from the harm of Pseudomonas aeruginosa via indirect seawead lysis

The local ecosystems, fishery and human health are all threatened by water blooms, so effectively controlling water blooms has become an urgent and challenging issue. Biological control of water blooms is given priority due to its low cost, high efficiency and environmental friendliness. In this study, Pseudomonas ZY-1 and Bacillus FY-1, two highly-effective algicidal bacteria strains which are able to indirectly lyse algae by separating and screening from the vigorous water body in the paddy alga of Northeast China were obtained. The two bacterial strains have stronger ability to lyse alga in the bacterial liquid concentration of 106 CFU/ml, and the alga-lysing rate on 7 d reached 84.03% and 83.11% respectively. The active substance secreted by ZY-1 is not sensitive to the changes of temperature and pH value, while as FY-1 cell-free filtrate is not stable in high temperature above 50 ℃ and pH of 5, it requires the sun light to have the algaecidal effect. The cell-free filtrates of strains ZY-1 and FY-1 had the best lysis effect on Microcystis aeruginosa cells, and the chlorophyll a content of algae decreased to 0.13 ± 0.02 mg/L and 0.14 ± 0.03 mg/L respectively and the Fv/Fm of Microcystis aeruginosa decreased by 97.22% after 7 days. The algaecidal process of ZY-1 and FY-1 may be that the cell-free filtrate inhibits the photosynthesis of Microcystis aeruginosa, and meanwhile it avoids the regeneration and repair of photosynthesis of algal cells by affecting the gene expression and damaging the repair system of algal cells, so the membrane lipid peroxidation is exacerbated and then the membrane of algal cells is broken, the algal cells can't do normal life activities, and finally the algal cell would be killed. The rice seedlings in the algal liquid treatment group are short and show root dysplasia, few roots and brown roots. After treated with cell-free filtrate of ZY-1 and FY-1, the oxidative damage of the rice is obviously reduced, and the harm from Microcystis aeruginosa is reduced, which has the repair effect to the roots of rice seedlings and its aboveground growth. The cell-free filtrate of FY-1 works better than ZY-1. The bacteria strains of ZY-1 and FY-1 have the indirect algaecide trait, which makes them the potential environmentally-friendly algaecidal bacteria and they show broad application in the agricultural production and the control of water blooms.

Diverse interactions between bacteria and microalgae: A review for enhancing harmful algal bloom mitigation and biomass processing efficiency

The interactions between bacteria and microalgae play pivotal roles in resource allocation, biomass accumulation, nutrient recycling, and species succession in aquatic systems, offering ample opportunities to solve several social problems. The escalating threat of harmful algal blooms (HABs) in the aquatic environment and the lack of cheap and eco-friendly algal-biomass processing methods have been among the main problems, demanding efficient and sustainable solutions. In light of this, the application of algicidal bacteria to control HABs and enhance algal biomass processing has been promoted in the past few decades as potentially suitable mechanisms to solve those problems. Hence, this comprehensive review aims to explore the diverse interaction modes between bacteria and microalgae, ranging from synergistic to antagonistic, and presents up-to-date information and in-depth analysis of their potential biotechnological applications, particularly in controlling HABs and enhancing microalgal biomass processing. For instance, several studies revealed that algicidal bacteria can effectively inhibit the growth of Microcystis aeruginosa, a notorious freshwater HAB species, with an antialgal efficiency of 24.87 %-98.8 %. The review begins with an overview of the mechanisms behind algae-bacteria interactions, including the environmental factors influencing these dynamics and their broader implications for aquatic ecosystems. It then provides a detailed analysis of the role of algicidal bacteria in controlling harmful algal blooms, as well as their role in bioflocculation and the pretreatment of microalgal biomass. Additionally, the review identifies and discusses the constraints and challenges in the biotechnological application of these interactions. By exploring the strategic use of algicidal bacteria, this review not only underscores their importance in maintaining aquatic environmental health but also in enhancing biomass processing efficiency. It offers valuable insights into future research avenues and the potential scalability of these applications, both in situ and at an industrial level.

Enhanced inhibitory efficiency against toxic bloom forming Raphidiopsis raciborskii by Streptomyces sp. HY through triple algicidal modes: Direct and indirect attacks combined with bioflocculation

Raphidiopsis raciborskii (R. raciborskii) forms harmful cyanobacterial blooms globally, and poses a great threat to the safety of drinking water and public health. There is a great need to develop eco-friendly biological alternative measures to mitigate mass blooms of R. raciborskii. However, previous rare studies on algicidal microorganisms against R. raciborskii restricted this aim. Recently, an algicidal bacterium Streptomyces sp. HY (designated HY) was identified with flavones producing ability, and could remove up to 98.73 % of R. raciborskii biomass within 48 h by directly attacking the cyanobacterium and release of algicidal substances (i.e., flavonoids) with a inoculum ratio of 5 %. Algicidal rate of HY was enhanced by 88.05 %, 89.33 % under dark and light, and full-light conditions respectively, when compared with the dark condition. Its algicidal substances were stable in a broad range of temperature (-80-55 °C) and pH (3-11) conditions, and all treated groups exhibited ≈ 100 % algicidal rate at day 3. HY treatment disrupted the photosynthesis system and triggered serious oxidative stress resulting in severe morphological injury. Thereby, HY treatment significantly affected expression levels of several essential genes (i.e., psbA, psaB, rbcL, ftsZ, recA, grpE), and simultaneously inhibited the biosynthesis and release of cylindrospermopsin. Yet, HY treatment didn't show any toxicity to zebrafish test embryos. Such results indicate that HY is a promising algicidal candidate strain to control global R. raciborskii blooms, and holds great promises for an effective biological measure to sustain water safety.

Antagonistic actions of Paucibacter aquatile B51 and its lasso peptide paucinodin toward cyanobacterial bloom-forming Microcystis aeruginosa PCC7806

Superior antagonistic activity against axenic Microcystis aeruginosa PCC7806 was observed with Paucibacter sp. B51 isolated from cyanobacterial bloom samples among 43 tested freshwater bacterial species. Complete genome sequencing, analyzing average nucleotide identity and digital DNA-DNA hybridization, designated the B51 strain as Paucibacter aquatile. Electron and fluorescence microscopic image analyses revealed the presence of the B51 strain in the vicinity of M. aeruginosa cells, which might provoke direct inhibition of the photosynthetic activity of the PCC7806 cells, leading to perturbation of cellular metabolisms and consequent cell death. Our speculation was supported by the findings that growth failure of the PCC7806 cells led to low pH conditions with fewer chlorophylls and down-regulation of photosystem genes (e.g., psbD and psaB) during their 48-h co-culture condition. Interestingly, the concentrated ethyl acetate extracts obtained from B51-grown supernatant exhibited a growth-inhibitory effect on PCC7806. The physical separation of both strains by a filter system led to no inhibitory activity of the B51 cells, suggesting that contact-mediated anti-cyanobacterial compounds might also be responsible for hampering the growth of the PCC7806 cells. Bioinformatic tools identified 12 gene clusters that possibly produce secondary metabolites, including a class II lasso peptide in the B51 genome. Further chemical analysis demonstrated anti-cyanobacterial activity from fractionated samples having a rubrivinodin-like lasso peptide, named paucinodin. Taken together, both contact-mediated inhibition of photosynthesis and the lasso peptide secretion of the B51 strain are responsible for the anti-cyanobacterial activity of P. aquatile B51.

Inactivation of Heterosigma akashiwo under UV/peroxydisulfate advanced disinfection system in marine waters

Heterosigma akashiwo (H. akashiwo) is recognized as a harmful algal bloom (HABs) species with a global distribution, capable of posing significant threats to marine ecosystems, particularly when spread through ship ballast water. This investigation focused on elucidating the inactivation kinetics and underlying mechanism of H. akashiwo through a combined ultraviolet irradiation and peroxydisulfate (UV/PDS) process. The results demonstrated a strong synergistic effect within the UV/PDS system, resulting in an inactivation of 0.78-ln and 2.67-ln within 40 min of UV and UV/PDS processes. The principal agents accountable for inactivation were identified as sulfate radicals (•SO4-) and hydroxyl radical (•OH), which exhibited a synergistic effect in the UV/PDS process. Furthermore, the study observed a negatively impact of seawater pH and salinity on the efficiency of inactivation. UV/PDS caused oxidative stress on algal cells, initially involving the participation of antioxidant enzymes in counteracting cellular damage, but this protective mechanism diminished as the reaction duration extended. The UV/PDS treatment not only inflicted damage upon H. akashiwo's photosynthetic system but also caused the extracellular release of DNA and algal organic matter (AOM) due to damaged cell membranes. Transcriptome analysis provided a molecular biology perspective on the cellular inactivation process. Upregulation of genes linked to photosynthesis and oxidative phosphorylation suggested a potential elevation in energy metabolism. In contrast, genes associated with cellular and metabolic processes, including glycolysis and the tricarboxylic acid cycle (TCA cycle), exhibited downregulation. Moreover, this treatment exerted an inhibitory influence on RNA polymerase and protein synthesis, resulting in the reduced expression of genetic information.

Algicidal Activity and Microcystin-LR Destruction by a Novel Strain Penicillium sp. GF3 Isolated from the Gulf of Finland (Baltic Sea)

The present article focuses on a strain of ascomycete GF3 isolated from a water sample taken in the Gulf of Finland. Based on phylogenetic analysis data, the isolate was identified as Penicillium sp. GF3. The fungus GF3 demonstrates algicidal activity towards cyanobacteria (98-100%). The algicidal effect on green algae did not exceed 50%. The isolate GF3 exhibits an indirect attack mode by releasing metabolites with algicidal and/or lytic activity into the environment. Moreover, the strain Penicillium sp. GF3 is able to degrade MC-LR. After 72 h of GF3 cultivation, the MC-LR content was reduced by 34.1% and 26.7% at initial 0.1 μg/mL and 0.45 μg/mL concentrations, respectively. The high stress resistance of the GF3 to toxic MC-LR is provided by a 1.5-fold activation of catalase activity and a change in the reduced glutathione content. Additionally, during the MC-LR biotransformation, a MC-LR-GSH conjugate and linearized MC-LR were identified. The linearized MC-LR in the presence of fungi capable of degrading MCs was revealed for the first time. Using Daphnia magna as a bioindicator, it was shown that the MC-LR biotransformation led to the formation of less toxic intermediates. The toxicity of the fungal filtrate is reduced by five times compared to the abiotic control. Our findings enhance the understanding of the role that ascomycete fungi have as potential bioagents for cyanoHABs to control and detoxify water bodies.

Identification of a Bacillus thuringiensis Q1 compound with algicidal activity

Bacillus thuringiensis Q1, isolated from the eutrophic waters of the Haihe River in Tianjin, possesses remarkable algae dissolving character. We determined the lytic effect of B. thuringiensis Q1 fermentation broth, and it proved to be pH- and temperature-stable. Then, we investigated the structure of the algicidal compound by high performance liquid chromatography, gas chromatography tandem quadrupole mass spectrometry and fourier transform infrared spectroscopy, and identified as purine-derived C12H15O5N5. To further understand B. thuringiensis Q1, we performed genome sequencing and analysis. The genome was 5341610 bp, with 35.31% GC content. Some elements involved in algicidal activity, such as quorum sensing pathway and ABC transporter were predicted. Our results reveal that B. thuringiensis Q1 can be used for biological control of harmful algal blooms.

A novel cyanolytic bacterium, Pseudomonas fluorescens BG-E as a potential biological control agent for freshwater bloom-forming cyanobacteria Pseudanabaena spp

The majority of bacterial antagonists identified to date are active against Microcystis. Therefore, this study aimed to isolate and characterize novel cyanolytic bacterial strains antagonistic against bloom-forming filamentous cyanobacteria. The bacterial strain BG-E isolated from the Bandagiriya Wewa in Sri Lanka was identified as Pseudomonas fluorescens (MZ007859) based on the 16S rRNA gene sequencing. BG-E showed 82% and 73% cyanolytic activity (CA) against Pseudanabaena sp. LW2 (MW288948) and Pseudanabaena lonchoides LW1 (MW288940), respectively, after 10 days of inoculation. The light microscopic images affirmed the complete disintegration in the filamentous structures of the tested Pseudanabaena species. The bacterial cell density of 15% v/v showed the CA with 95% and 89% cell lysis, respectively, in P. lonchoides and Pseudanabaena sp. LW2. Moreover, the results showed that >50% CA could be achieved by 0.100 and 1.00 (OD₇₃₀ ) cell densities for these same species. The highest CA of the cell-free supernatant of BG-E against P. lonchoides and bacterial culture against Pseudanabaena sp. LW2 illustrated the species-specific mode of action of BG-E. Although BG-E efficiently lysed the tested cyanobacterial species, the results of the MC-biodegradation assay confirmed its inability to degrade MC-LR cyanotoxin. Further, the BG-E strain lacks the mlrABCD gene cluster which is known to be responsible for the enzymatic degradation of MCs. The overall findings highlighted the applicability of P. fluorescens BG-E as a biological controlling agent to terminate blooms of freshwater filamentous cyanobacteria genus Pseudanabaena. The incorporation of cyanotoxin-degrading heterotrophic bacteria is recommended as a means of controlling toxic Pseudanabaena blooms.

Discovery of a High-Efficient Algicidal Bacterium against Microcystis aeruginosa Based on Examinations toward Culture Strains and Natural Bloom Samples

Harmful cyanobacterial blooms occur worldwide and pose a great threat to aquatic ecosystems and public health. The application of algicidal bacteria represents an eco-friendly strategy for controlling harmful cyanobacterial blooms; thus, searching for a high efficiency of algicidal bacteria has been becoming an important and continuous task in science. Herein, we identified a bacterial strain coded Streptomyces sp. HY with a highly algicidal activity, and investigated its algicidal efficiency and mechanism against Microcystis aeruginosa. The strain HY displayed high algicidal activity toward Microcystis aeruginosa cells, with a removal rate of 93.04% within 2 days via indirect attack. Streptomyces sp. HY also showed the ability to lyse several genera of cyanobacterial strains, including Dolichospermum, Pseudanabaena, Anabaena, and Synechocystis, whereas it showed a minor impact on the green alga Scenedesmus obliquus, demonstrating its selectivity specially for targeting cyanobacteria. Its algicidal mechanism involved damages to the photosynthesis system, morphological injury of algal cells, oxidative stress, and dysfunction of the DNA repair system. Furthermore, HY treatment reduced the expression levels of genes (mcyB and mcyD) related to microcystin biosynthesis and decreased the total content of microcystin-leucine-arginine by 79.18%. Collectively, these findings suggested that the algicidal bacteria HY is a promising candidate for harmful cyanobacterial bloom control.

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.

The inhibitory effects of simulated light sources on the activity of algae cannot be ignored in photocatalytic inhibition

Harmful algal blooms (HABs) destroy the balance of the aquatic ecosystem, causing huge economic losses and even further endangers human health. In addition to traditional methods of algae removal, photocatalytic inhibition of algae is drawing more and more interests with rich application scenarios and considerable potential. Simulated visible light sources are used to excite photocatalytic materials and optimize their performance. However, most of the light irradiation intensities used in the study exceeded 50 mW/cm². And the effects of intense light irradiation conditions on algal growth have rarely been addressed in previous studies. So we focused on the effect of different intensity of light irradiation on the growth of algae. We explored the relationship between light irradiation intensity and algal inactivation rate, and investigated the changes in ROS levels in algal cells under different light irradiation and the resulting response of the antioxidant system. We have found that several major antioxidant enzyme activities, such as SOD and CAT, were significantly higher and lipid peroxidation products (MDA) were accumulating. Intense light irradiation had the most direct effect on the photosynthetic system of algal cells, with the photosynthetic rate and relative electron transfer rate decaying to almost 0 within 30 min, indicating that algal photosynthesis was inhibited in a fairly short period of time. We further observed the physiological and morphological changes of algal cells during this process using TEM and found that the progressive dissolution of the cell membrane system and the damage of organelles associated with photosynthesis play a major role in promoting cell death. We thus conclude that light irradiation has a significant effect on the physiological activity of algal cells and is a non-negligible factor in the study of photocatalytic removal of harmful algae. It will provide theoretical guidance for the future study of photocatalysis on algae inhibition.

Inhibitory effects of Ipomoea cairica extracts on the harmful algae Phaeocystis globosa

Ipomoea cairica (L.) Sweet is an invasive plant that cause serious invasion and damage in South China. Phaeocystis globosa is a common harmful algal bloom species on the southeast coast of China. Both species cause great environmental disturbances and serious economic damage to the localregion. This study explored the potential inhibitory effects of I. cairica leaf extracts on P. globosa. The results showed that solitary cells growth was inhibited at extract concentrations higher than 0.25 % (v/v). Although the colony diameter did not change, and the colony number increased rapidly in the first 36 h, we found that cells in the colonies had been damaged using scanning electron microscope and SYTOX-Green staining at 48 h. In addition, the rapid light-response curve of cells treated with extracts decreased, along with down-regulation of photosynthesis-related genes (psbA, psbD, and rbcL), suggesting damage to the photosynthetic system. Finally, the activities of antioxidant enzymes including superoxide dismutase, peroxidase, and catalase increased with increasing treatment time, indicating that cells activate antioxidant enzyme defense systems to alleviate the production of reactive oxygen species (ROS). Increased ROS levels disrupt cell membranes, alter cellular ultrastructures, and ultimately lead to cell death. This study not only achieved the reuse of invasive plant resources, but also demonstrated that I. cairica leaf extract has potential value as an algaecide.

Algicidal activity of Morganella morganii against axenic and environmental strains of Microcystis aeruginosa: Compound combination effects

Cyanobacterial harmful algal blooms (cyanoHABs) are a global problem with serious consequences for public health and many sectors of the economy. The use of algicidal bacteria as natural antagonists to control bloom-forming cyanobacteria is a topic of growing interest. However, there are still unresolved questions that need to be addressed to better understand their mode of action and to implement effective mitigation strategies. In this study, thirteen bacterial strains isolated from both scums and concentrated bloom samples exhibited algicidal activity on three Microcystis aeruginosa strains with different characteristics: the axenic microcystin (MC)-producing strain M. aeruginosa PCC7820 (MaPCC7820), and two environmental (non-axenic) M. aeruginosa strains isolated from two different water bodies in Poland, one MC-producer (MaSU) and another non-MC-producer (MaPN). The bacterial strain SU7S0818 exerted the highest average algicidal effect on the three cyanobacterial strains. This strain was identified as Morganella morganii (99.51% similarity) by the 16S rRNA gene analyses; hence, this is the first study that demonstrates the algicidal properties of these ubiquitous bacteria. Microscopic cell counting and qPCR analyses showed that M. morganii SU7S0818 removed 91%, 96%, and 98.5% of MaPCC7820, MaSU and MaPN cells after 6 days of co-culture, respectively. Interestingly, the ultra-high-performance liquid chromatography-tandem mass spectrometer (UHPLC-MS/MS) analyses showed that this bacterium was involved on the release of several substances with algicidal potential. It was remarkable how the profile of some compounds evolved over time, as in the case of cadaverine, tyramine, cyclo[Pro-Gly] and cyclo[Pro-Val]. These dynamic changes could be attributed to the action of M. morganii SU7S0818 and the presence of associated bacteria with environmental cyanobacterial strains. Therefore, this study sheds light on how algicidal bacteria may adapt their action on cyanobacterial cells by releasing a combination of compounds, which is a crucial insight to exploit them as effective biological tools in the control of cyanoHABs.

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.

High-Throughput 16 S rRNA Gene Sequencing Reveals Bacterial Diversity of Infant Formula Production Line Samples in Spring and Summer

The trend of low breastfeeding rates increases the demand for infant milk formula (IMF) worldwide, but the use of IMF may be one of the causes of bacterial infections in infants. Complete sterility in the whole production line of IMF cannot be guaranteed; therefore, it is necessary to closely monitor the microbial content in the process. In the present study, an IMF powder production line based on the wet mixing process was sampled at 27 suspicious points in spring and summer to analyze the bacterial diversity by high-throughput sequencing. We found that 70 and 69 different bacterial phyla were present in spring and summer samples, respectively, with Proteobacteria and Firmicutes being the dominant phyla (>80% relative abundance). Moreover, 13 dominant genera each were present in spring (e. g., Pseudomonas and Lactococcus) and summer (e. g., Pseudomonas, Bacillus, and Streptococcus). Samples associated with workers showed higher bacterial species diversity (Shannon index) and richness (Chao1 index) in summer than in spring. The bacterial community composition showed high similarity between liquid milk after pasteurization and concentrated milk after evaporation. The potential bacterial pathogens were identified as Pseudomonas aeruginosa in spring and Acinetobacter baumannii in summer. Through retrospective analysis of the two opportunistic pathogens identified, it was found that the workshop environment was the potential contamination point in spring, whereas the auxiliary ingredients were the potential source of contamination in summer. The results highlight the effect of season on bacterial diversity associated with the production process of IMF and are useful in controlling the microbial quality and safety of infant dairy products.

Microcystis colony formation: Extracellular polymeric substance, associated microorganisms, and its application

Microcystis sp., amongst the most prevalent bloom-forming cyanobacteria, is typically found as a colonial form with multiple microorganisms embedded in the mucilage known as extracellular polymeric substance. The colony-forming ability of Microcystis has been thoroughly investigated, as has the connection between Microcystis and other microorganisms, which is crucial for colony development. The following are the key subjects to comprehend Microcystis bloom in depth: 1) key issues related to the Microcystis bloom, 2) features and functions of extracellular polymeric substance, as well as diversity of associated microorganisms, and 3) applications of Microcystis-microorganisms interaction including bloom control, polluted water bioremediation, and bioactive compound production. Future research possibilities and recommendations regarding Microcystis-microorganism interactions and their significance in Microcystis colony formation are also explored. More information on such interactions, as well as the mechanism of Microcystis colony formation, can bring new insights into cyanobacterial bloom regulation and a better understanding of the aquatic ecosystem.

Combined Effect of NZVI and H2O2 on the Cyanobacterium Microcystis aeruginosa: Performance and Mechanism

In order to eliminate the harmful cyanobacterium Microcystis aeruginosa and the algal organic matters (AOMs) produced by M. aeruginosa, the combined process of nanoscale zero-valent iron (NZVI) and hydrogen peroxide (H₂O₂) has been carried out, and the removal mechanism has also been clarified. As the initial cyanobacterial cell concentration is 1.0 (±0.05) × 10⁵ cells·mL^-1, all the treatments of NZVI, H₂O₂, and NZVI/H₂O₂ have inhibition effects on both the Chl a contents and photosynthetic pigments, with the Chl a removal efficiency of 47.3%, 80.5%, and 90.7% on the 5th day, respectively; moreover, the variation of ζ potential is proportional to that of the Chl a removal efficiency. The malondialdehyde content and superoxide dismutase activity are firstly increased and ultimately decreased to mitigate the oxidative stress under all the treatments. Compared with NZVI treatment alone, the oxidation of the H₂O₂ and NZVI/H₂O₂ processes can effectively destroy the antioxidant enzyme system and then inactivate the cyanobacterial cells, which further leads to the release of photosynthetic pigments and intracellular organic matters (IOM); in addition, the IOM removal efficiency (in terms of TOC) is 61.3% and 54.1% for the H₂O₂ and NZVI/H₂O₂ processes, respectively. Although NZVI is much more effective for extracellular organic matters (EOM) removal, it is less effective for IOM removal. The results of the three-dimensional EEM fluorescence spectra analysis further confirm that both H₂O₂ and NZVI/H₂O₂ have the ability to remove fluorescent substances from EOM and IOM, due to the oxidation mechanism; while NZVI has no removal effect for the fluorescent substances from EOM, it can remove part of fluorescent substances from IOM due to the agglomeration. All the results demonstrate that the NZVI/H₂O₂ process is a highly effective and applicable technology for the removal of M. aeruginosa and AOMs.

The Effect of Algicidal and Denitrifying Bacteria on the Vertical Distribution of Cyanobacteria and Nutrients

Algicidal bacteria combined with the ability of aerobic denitrification is considered to be a promising way to control harmful cyanobacterial bloom and remove nitrogen. However, the effect of these bacteria on the vertical distribution of colonial cyanobacteria and nutrients remained unknown. In this study, two algicidal and denitrifying bacteria were respectively co-cultured with the colonial Microcystis aeruginosa to construct the microcosm systems, and then the cyanobacteria number, the ratio of bacterial to cyanobacterial abundance, the content of dissolved nitrogen, phosphorus and organic carbon in different water layers were investigated. The results showed that the distribution difference of Microcystis among the vertical water layers was further enlarged due to the short-term influence of algicidal bacteria Brevundimonas diminuta and Pseudomonas stutzeri. The number of Microcystis in the lower layer was further reduced by the inhibitory effect of the algicidal bacteria. However, there was a dramatic increase in the number of Microcystis in the upper layer, even when the ratio of algicidal bacteria to cyanobacteria increased significantly. B. diminuta and P. stutzeri both greatly promoted the removal of dissolved total nitrogen in the upper and middle layers of cyanobacteria blooming water, but they also boosted the release of dissolved phosphorus in all layers. These results enable us to better understand the possible limitations of algicidal bacteria in their application to control cyanobacteria blooms.

Recent Advances in the Research on the Anticyanobacterial Effects and Biodegradation Mechanisms of Microcystis aeruginosa with Microorganisms

Harmful algal blooms (HABs) have attracted great attention around the world due to the numerous negative effects such as algal organic matters and cyanobacterial toxins in drinking water treatments. As an economic and environmentally friendly technology, microorganisms have been widely used for pollution control and remediation, especially in the inhibition/biodegradation of the toxic cyanobacterium Microcystis aeruginosa in eutrophic water; moreover, some certain anticyanobacterial microorganisms can degrade microcystins at the same time. Therefore, this review aims to provide information regarding the current status of M. aeruginosa inhibition/biodegradation microorganisms and the acute toxicities of anticyanobacterial substances secreted by microorganisms. Based on the available literature, the anticyanobacterial modes and mechanisms, as well as the in situ application of anticyanobacterial microorganisms are elucidated in this review. This review aims to enhance understanding the anticyanobacterial microorganisms and provides a rational approach towards the future applications.

Algicidal Properties of Microbial Fermentation Products on Inhibiting the Growth of Harmful Dinoflagellate Species

The fermentation processes of algicidal bacteria offer an eco-friendly and promising approach for controlling harmful algae blooms (HABs). The strain Ba3, previously isolated and identified as Bacillus sp., displays robust algicidal activity against HABs dinoflagellate in particular. Microbial fermentation products have also been found to provide metabolites with multiple bioactivities, which has been shown to reduce harmful algae species’ vegetative cells and thus reduce red tide outbreaks. In this study, the microbial fermentation of algicidal bacterium Ba3 was analyzed for its potential ability of algicidal compounds. A treatment time increased the algicidal efficiency of the fermentation products against Prorocentrum donghaiense (91%) and Alexandrium tamarense (82%). Among the treatment groups, the changing trend for the 2% treatment group was faster than that for the other treatments, showing that the inhibition rate could reach 99.1% in two days. Active components were separated by organic solvent extraction and macroporous resin, and the molecular weight of the active components was analyzed by LC-MS. The result shows that the microbial fermentation products offer a potential, not practical use for controlling the outbreaks of dinoflagellate blooms. As a result of its potential application for inhibiting HABs, these findings provide an encouraging basis for promoting large-scale fermentation production and the controlling the outbreaks of red tide.

Algicidal effect of tryptoline against Microcystis aeruginosa: Excess reactive oxygen species production mediated by photosynthesis

Cyanobacterial blooms significantly decrease water quality and can damage ecosystems and, as such, require efficient control methods. Algicidal bacteria and their associated substances are promising tools for controlling cyanobacterial blooms; however, their specific algicidal mechanisms remain unclear. Therefore, the current study sought to investigate the algicidal mechanism of tryptoline (1,2,3,4-tetrahydro-9 h-pyrido[3,4-b]indole) against Microcystis aeruginosa, with a specific focus on the contribution made by reactive oxygen species (ROS), the underlying mechanisms of ROS increase, as well as the photosystem response. Results show that the algicidal ratio of tryptoline significantly and positively correlates with algal ROS. Moreover, 93.79% of the algicidal ratio variation is attributed to ROS in the tryptoline group, while only 47.75% can be attributed to ROS in the tryptoline + N-acetyl-L-cysteine (NAC) group, where ROS are partially scavenged by NAC. In the presence of tryptoline, algicidal effect and ROS levels were significantly enhanced in the presence of light as compared to those in the dark (P < 0.001). Hence, the increase in ROS production attributed to tryptoline is primarily affected by the presence of light and photosynthesis. Additionally, tryptoline significantly reduces F_v/F_m, PI_ABS, ET_o/RC, and the expression of psaB and psbA genes related to photosynthesis, while increasing V_j and DI_o/RC (P < 0.05). These results suggest that tryptoline hinders algal photosynthesis by significantly decreasing photosynthetic efficiency and carbon assimilation, inhibiting photochemical electron transfer, and increasing closed reaction centers and energy loss. Moreover, following partial blockade of the photosynthetic electron transfer from Q_A to Q_B by diuron (3-(3-4-dichlorophenyl)-1,1-dimethylurea), the ROS of algae exposed to tryptoline is significantly decreased. Thus, tryptoline inhibits electron transfer downstream of Q_A, which increase the number of escaping electron and thereby increase ROS generation. Collectively, this study describes the algicidal mechanism of tryptoline against M. aeruginosa and highlights the critical factors associated with induction of algicidal activity.

Algicidal mechanism of Raoultella ornithinolytica against Microcystis aeruginosa: Antioxidant response, photosynthetic system damage and microcystin degradation

Water eutrophication caused by harmful algal blooms (HABs) occurs worldwide. It causes huge economic losses and has serious and potentially life-threatening effects on human health. In this study, the bacterium Raoultella sp. S1 with high algicidal efficiency against the harmful algae Microcystis aeruginosa was isolated from eutrophic water. The results showed that Raoultella sp. S1 initially flocculated the algae, causing the cells to sediment within 180 min and then secreted soluble algicidal substances that killed the algal cells completely within 72 h. The algicidal activity was stable across the temperature range -85.0 to 85.0 °C and across the pH range 3.00-11.00. Scanning electron microscopy (SEM) revealed the crumpling and fragmentation of cells algal cells during the flocculation and lysis stages. The antioxidant system was activated under conditions of oxidative stress, causing the increased antioxidant enzymes activities. Meanwhile, the oxidative stress response triggered by the algicidal substances markedly increased the malondialdehyde (MDA) and glutathione (GSH) content. We investigated the content of Chl-a and the relative expression levels of genes related to photosynthesis, verifying that the algicidal compounds attack the photosynthetic system by degrading the photosynthetic pigment and inhibiting the expression of key genes. Also, the results of photosynthetic efficiency and relative electric transport rate confirmed that the photosynthetic system in algal cells was severely damaged within 24 h. The algicidal effect of Raoultella sp. S1 against Microcystis aeruginosa was evaluated by analyzing the physiological response and photosynthetic system impairment of the algal cells. The concentration of microcystin-LR (MC-LR) slightly increased during the process of algal cells ruptured, and then decreased below its initial level due to the biodegradation of Raoultella sp. S1. To further investigate the algicidal mechanism of Raoultella sp. S1, the main components in the cell-free supernatant was analyzed by UHPLC-TOF-MS. Several low-molecular-weight organic acids might be responsible for the algicidal activity of Raoultella sp. S1. It is concluded that Raoultella sp. S1 has the potential to control Microcystis aeruginosa blooms.

Effects of two algicidal substances, ortho-tyrosine and urocanic acid, on the growth and physiology of Heterosoigma akashiwo

Heterosigma akashiwo is a commonly found harmful microalgae, however, there are only few studies on its control using algicidal components particularly those identified from algicidal bacteria. In our previous study, ortho-tyrosine and urocanic acid identified from Bacillus sp. B1 showed a significantly high algicidal effect on H. akashiwo. The growth inhibition rates of H. akashiwo after 96 h of treatment with 300 μg/mL o-tyrosine and 500 μg/mL urocanic acid were 91.06% and 88.07%, respectively. Through non-destructive testing by Pulse Amplitude Modulation fluorometry and flow cytometer, the effects of o-tyrosine and urocanic acid on H. akashiwo PS II and physiological parameters (cell volume, mitochondrial membrane potential, and membrane permeability) were estimated. This study shows that o-tyrosine affected the photosynthesis system of H. akashiwo, decreased the mitochondrial membrane potential, and increased the membrane permeability of the algal cells. Treatment with urocanic acid decreased the mitochondrial membrane potential, resulting in the inhibition of algal cell growth and reproduction, but had little effect on membrane permeability and photosynthetic system. Our results may imply that when uridine degrades, surviving H. akashiwo cells may be reactivated. Therefore, o-tyrosine and urocanic acid have the potential to become new biological algicides, which can effectively control the growth of H. akashiwo.

Cyanobacterial bloom induces structural and functional succession of microbial communities in eutrophic lake sediments

Cyanobacterial blooms have considerable effects on lacustrine microbial communities. The current study explored the temporal pattern of sedimentary archaea and bacteria during cyanobacterial bloom in a eutrophic lake. With the sampling period divided into bloom phase, interval phase and end phase according to the variation of physicochemical parameters, the structures and functions of both kingdoms presented a significant difference among phases. Bloom phases could be characterized with the lowest diversity and up-regulated functions in biodegradation of cyanobacterial metabolites driven by bacteria. Archaeal community showed an increased metabolic function during interval phases, including active methanogenesis sensitive to carbon input. The highest diversity and an enrichment of hub genera in microbial network were both observed in end phase, allowing for closer cooperation among groups involved in cyanobacteria-derived organic matter transformation. Although the archaeal community was less variable or diverse than bacteria, methanogenic functions dramatically fluctuated with cyanobacterial dynamics. And microbial groups related to methane cycling played an important role in microbial network. The results provided new insights into temporal dynamics of lacustrine microbial communities and microbial co-occurrence, and highlighted the significant ecological role of methane cycling-related microbes in lake sediments under the influence of cyanobacterial blooms.

Transcriptional Analysis of Microcystis aeruginosa Co-Cultured with Algicidal Bacteria Brevibacillus laterosporus

Harmful algal blooms caused huge ecological damage and economic losses around the world. Controlling algal blooms by algicidal bacteria is expected to be an effective biological control method. The current study investigated the molecular mechanism of harmful cyanobacteria disrupted by algicidal bacteria. Microcystis aeruginosa was co-cultured with Brevibacillus laterosporus Bl-zj, and RNA-seq based transcriptomic analysis was performed compared to M. aeruginosa, which was cultivated separately. A total of 1706 differentially expressed genes were identified, which were mainly involved in carbohydrate metabolism, energy metabolism and amino acid metabolism. In the co-cultured group, the expression of genes mainly enriched in photosynthesis and oxidative phosphorylation were significantly inhibited. However, the expression of the genes related to fatty acid synthesis increased. In addition, the expression of the antioxidant enzymes, such as 2-Cys peroxiredoxin, was increased. These results suggested that B. laterosporus could block the electron transport by attacking the PSI system and complex I of M. aeruginosa, affecting the energy acquisition and causing oxidative damage. This further led to the lipid peroxidation of the microalgal cell membrane, resulting in algal death. The transcriptional analysis of algicidal bacteria in the interaction process can be combined to explain the algicidal mechanism in the future.

Biotechnological applications of Bacillus licheniformis

Bacillus licheniformis is a Gram positive spore-forming bacterial species of high biotechnological interest with numerous present and potential uses, including the production of bioactive compounds that are applied in a wide range of fields, such as aquaculture, agriculture, food, biomedicine, and pharmaceutical industries. Its use as an expression vector for the production of enzymes and other bioproducts is also gaining interest due to the availability of novel genetic manipulation tools. Furthermore, besides its widespread use as a probiotic, other biotechnological applications of B. licheniformis strains include: bioflocculation, biomineralization, biofuel production, bioremediation, and anti-biofilm activity. Although authorities have approved the use of B. licheniformis as a feed additive worldwide due to the absence of toxigenic potential, some probiotics containing this bacterium are considered unsafe due to the possible transference of antibiotic resistance genes. The wide variability in biological activities and genetic characteristics of this species makes it necessary to establish an exact protocol for describing the novel strains, in order to evaluate its biotechnological potential.

Facilitating harmful algae removal in fresh water via joint effects of multi-species algicidal bacteria

Harmful algae blooms posing serious threats to the ecological environment occur frequently across the world. Multi-species algicidal bacteria were enriched by utilizing immobilized carriers in a pilot scale experiment, which significantly promoted the effect of algal control in the reactors. Under the optimal condition, the algicidal ratio and chlorophyll a degradation rate reached 87.69% and 47.00 μg/(L·d), respectively. The growth of Cyanophyta, diatom, Dinoflagellate and Cryptophyta was inhibited significantly by the joint action of algicidal bacteria and light shading of fillers, accounting for 53.74% and 36.47%, respectively. The results of 16S rRNA high-throughput sequencing suggested algicidal bacteria (10.17%) belonging to 13 genera were enriched. Among the algicidal process, Bacillus and Pseudomonas played crucial roles. Fluorescence spectroscopy and UV₂₅₄ were adopted to assess the release of dissolved organic matter (DOM) and the precursors of disinfection by-products (DBPs). Two efficient algicidal strains (C1, C4) were isolated which showed high homology with Enterobacter asburiae JCM6051(T) and Pseudomonas simiae oli(T), respectively. This study provided new insights into the in-situ bioremediation of eutrophication in fresh water.

Isolation and Identification of Two Algae-Lysing Bacteria against Microcystis aeruginosa

Algae blooms present an environmental problem worldwide. In response to the outbreak of harmful algal blooms in cyanobacteria, the role of biological control has drawn wide attention, particularly for algicidal bacteria. The mechanism underlying algicidal activity was determined in our study. Algae-lysing bacteria used were separated from water and sediment collected from the Fenhe scenic spot of Taiyuan. Genetic and molecular identification was conducted by polymerase chain reaction amplification based on 16S rDNA gene. These bacterial strains were identified as Raoultella planticola and Aeromonas sp. The algae-lysing characteristics were evaluated on Microcystis aeruginosa. For the two algicidal bacteria, the high inoculation ratio (>8%) of bacteria strains contributed to the lytic effect. M. aeruginosa could be completely removed by these strains at different cell ages. However, the time used decreased with an increase in cell age. The removal rate was increased while M. aeruginosa was in the lag and logarithmic phases. The earlier bacteria strains could be inoculated, the sooner all algae could be removed. Both algicidal substances were protein, which could destroy the photosynthetic systems and break the cell of M. aeruginosa. The algicidal bacteria strain has important theoretical and practical significance for economic and feasible algae removal and provides good germplasm resources and technical support for the control of cyanobacterial bloom.