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

Role of microalgae-bacterial consortium in wastewater treatment: A review

In the global effort to reduce CO2 emissions, the concurrent enhancement of pollutant degradation and reductions in fossil fuel consumption are pivotal aspects of microalgae-mediated wastewater treatment. Clarifying the degradation mechanisms of bacteria and microalgae during pollutant treatment, as well as regulatory biolipid production, could enhance process sustainability. The synergistic and inhibitory relationships between microalgae and bacteria are introduced in this paper. The different stimulators that can regulate microalgal biolipid accumulation are also reviewed. Wastewater treatment technologies that utilize microalgae and bacteria in laboratories and open ponds are described to outline their application in treating heavy metal-containing wastewater, animal husbandry wastewater, pharmaceutical wastewater, and textile dye wastewater. Finally, the major requirements to scale up the cascade utilization of biomass and energy recovery are summarized to improve the development of biological wastewater treatment.

Revealing the algicidal characteristics of Maribacter dokdonensis: An investigation into bacterial strain P4 isolated from Karenia mikimotoi bloom water

Harmful algal blooms (HABs) are a global environmental concern, causing significant economic losses in fisheries and posing risks to human health. Algicidal bacteria have been suggested as a potential solution to control HABs, but their algicidal efficacy is influenced by various factors. This study aimed to characterize a novel algicidal bacterium, Maribacter dokdonensis (P4), isolated from a Karenia mikimotoi (Hong Kong strain, KMHK) HAB and assess the impact of P4 and KMHK's doses, growth phase, and algicidal mode and the axenicity of KMHK on P4's algicidal effect. Our results demonstrated that the algicidal effect of P4 was dose-dependent, with the highest efficacy at a dose of 25% v/v. The study also determined that P4's algicidal effect was indirect, with the P4 culture and the supernatant, but not the bacterial cells, showing significant effects. The algicidal efficacy was higher when both P4 and KMHK were in the stationary phase. Furthermore, the P4 culture at the log phase could effectively kill KMHK cells at the stationary phase, with higher algicidal efficacy in the bacterial culture than that of the supernatant alone. Interestingly, P4's algicidal efficacy was significantly higher when co-culturing with xenic KMHK (~90% efficacy at day 1) than that with the axenic KMHK (~50% efficacy at day 1), suggesting the presence of other bacteria could regulate P4's algicidal effect. The bacterial strain P4 also exhibited remarkable algicidal efficacy on four other dinoflagellate species, particularly the armored species. These results provide valuable insights into the algicidal effect of M. dokdonensis on K. mikimotoi and on their interactions.

Influence of different cyanobacterial treatment methods on phosphorus cycle in shallow lake microcosms

Cyanobacterial bloom is a pressing issue affecting water supply security and ecosystem health. Phosphorus (P) released from cyanobacterial bloom during recession is one of the most important components involved in the lake P cycle. However, little is known about the consequences and mechanisms of the P cycle in overlying water and sediment due to the anthropogenic treatments of cyanobacterial blooms. In this study, treatment methods using hydrogen peroxide (H2O2), polyaluminum chloride (PAC), and the feces of silver carp were investigated for their influence on the P cycle using microcosm experiments. Results showed that H2O2 treatment significantly increased the internal cycle of sediment-related P, while PAC treatment showed minor effects. H2O2 and PAC treatment suppressed the release of P from sediment before day 10 but promoted the release of P on day 20, while silver carp treatment suppressed the release of P during the whole experiment. The reductive dissolution of iron oxide-hydroxide was the major factor affects the desorption of P. Path analyses further suggested that overlying water properties such as dissolved oxygen (DO) and oxidation-reduction potential (ORP) play critical roles in the treatment-induced sediment P release. Our results quantify the endogenous P diffusion fluxes across the sediment-water interface attributed to cyanobacterial treatments and provide useful guidance for the selection of controlling methods, with silver carp being the most recommended of the three methods studied.

Periodic Addition of Glucose Suppressed Cyanobacterial Abundance in Additive Lake Water Samples during the Entire Bloom Season

Previously, we showed that prophylactic addition of glucose to Harsha Lake water samples could inhibit cyanobacteria growth, at least for a short period of time. The current study tested cyanobacterial control with glucose for the entire Harsha Lake bloom season. Water samples (1000 ml) were collected weekly from Harsha Lake during the algal-bloom season starting June 9 and lasting until August 24, 2022. To each of two 7-liter polypropylene containers, 500 ml of Harsha Lake water was added, and the containers were placed in a controlled environment chamber. To one container labeled "Treated," 0.15 g of glucose was added, and nothing was added to the container labeled "Control." After that, three 25 ml samples from each container were collected and used for 16S rRNA gene sequencing each week. Then 1000 ml of Harsha Lake water was newly collected each week, with 500 ml added to each container, along with the addition of 0.15 g glucose to the "Treated" container. Sequencing data were used to examine differences in the composition of bacterial communities between Treated and Control containers. Treatment with glucose altered the microbial communities by 1) reducing taxonomic diversity, 2) largely eliminating cyanobacterial taxa, and 3) increasing the relative abundance of subsets of non-cyanobacterial taxa (such as Proteobacteria and Actinobacteriota). These effects were observed across time despite weekly inputs derived directly from Lake water. The addition of glucose to a container receiving weekly additions of Lake water suppressed the cyanobacterial populations during the entire summer bloom season. The glucose appears to stimulate the diversity of certain bacterial taxa at the expense of the cyanobacteria.

Sustainable bioremediation technologies for algal toxins and their ecological significance

The emergence of algal toxins in water ecosystems poses a significant ecological and human health concern. These toxins, produced by various algal species, can lead to harmful algal blooms, and have far-reaching consequences on biodiversity, food chains, and water quality. This review explores the types and sources of algal toxins, their ecological impacts, and the associated human health risks. Additionally, the review delves into the potential of bioremediation strategies to mitigate the effects of algal toxins. It discusses the role of microorganisms, enzymes, and algal-bacterial interactions in toxin removal, along with engineering approaches such as advanced oxidation processes and adsorbent utilization. Microbes and enzymes have been studied for their environmentally friendly and biocompatible properties, which make them useful for controlling or removing harmful algae and their toxins. The challenges and limitations of bioremediation are examined, along with case studies highlighting successful toxin control efforts. Finally, the review outlines future prospects, emerging technologies, and the need for continued research to effectively address the complex issue of algal toxins and their ecological significance.

Synthesis of Cu2+ doped biochar and its inactivation performance of Microcystis aeruginosa: Significance of synergetic effect

The harmful cyanobacteria bloom is frequently occurring in the aquatic environment and poses a tremendous threat to both aquatic organisms and ecological function. In this study, a series of Cu2+ doped biochar (BC) composites (Cu-BCs) with different loading ratios (0.1 %-5 wt %) (Cu-BC-0.1/0.5/1/2.5/5) was successfully fabricated through a one-step adsorption method for in-situ inactivation of Microcystis aeruginosa and simultaneous removal of microcystin-LR (MC-LR). Compared with the single BC/CuSO4 and other Cu-BCs composites, the Cu-BC-2.5 exhibited the best algae inactivation performance with the lowest 72 h medium effective concentration (EC50) value of 0.34 mg/L and highest chlorophyll α degradation efficiency of 8.31 g/g. Notably, the as-prepared Cu-BC-2.5 maintained good inactivation performance in the near-neutral pH (6.5-8.5), and the presence of humic acid and salts such as Na2CO3 and NaCl. The outstanding inhibitory effect of the Cu-BC-2.5 could be explained by the synergetic effect between biochar and Cu2+, which greatly elevated reactive oxygen species (ROS) intensity and in turn led to severe membrane damage and collapse of the antioxidant system. Additionally, the Cu-BC-2.5 could simultaneously remove the released microcystin-LR (MC-LR) throughout the inactivation process and prevent secondary pollution, thus offering a new insight into the alleviation of harmful cyanobacteria in aquatic environment.

Meta-organism gene expression reveals that the impact of nitrate enrichment on coral larvae is mediated by their associated Symbiodiniaceae and prokaryotic assemblages

BACKGROUND

Coral meta-organisms consist of the coral, and its associated Symbiodiniaceae (dinoflagellate algae), bacteria, and other microbes. Corals can acquire photosynthates from Symbiodiniaceae, whilst Symbiodiniaceae uses metabolites from corals. Prokaryotic microbes provide Symbiodiniaceae with nutrients and support the resilience of corals as meta-organisms. Eutrophication is a major cause of coral reef degradation; however, its effects on the transcriptomic response of coral meta-organisms remain unclear, particularly for prokaryotic microbes associated with corals in the larval stage. To understand acclimation of the coral meta-organism to elevated nitrate conditions, we analyzed the physiological and transcriptomic responses of Pocillopora damicornis larvae, an ecologically important scleractinian coral, after 5 days of exposure to elevated nitrate levels (5, 10, 20, and 40 µM).

RESULTS

The major differentially expressed transcripts in coral, Symbiodiniaceae, and prokaryotic microbes included those related to development, stress response, and transport. The development of Symbiodiniaceae was not affected in the 5 and 20 µM groups but was downregulated in the 10 and 40 µM groups. In contrast, prokaryotic microbe development was upregulated in the 10 and 40 µM groups and downregulated in the 5 and 20 µM groups. Meanwhile, coral larval development was less downregulated in the 10 and 40 µM groups than in the 5 and 20 µM groups. In addition, multiple larval, Symbiodiniaceae, and prokaryotic transcripts were significantly correlated with each other. The core transcripts in correlation networks were related to development, nutrient metabolism, and transport. A generalized linear mixed model, using least absolute shrinkage and selection operator, demonstrated that the Symbiodiniaceae could both benefit and cost coral larval development. Furthermore, the most significantly correlated prokaryotic transcripts maintained negative correlations with the physiological functions of Symbiodiniaceae.

CONCLUSIONS

Results suggested that Symbiodiniaceae tended to retain more nutrients under elevated nitrate concentrations, thereby shifting the coral-algal association from mutualism towards parasitism. Prokaryotic microbes provided Symbiodiniaceae with essential nutrients and may control Symbiodiniaceae growth through competition, whereby prokaryotes can also restore coral larval development inhibited by Symbiodiniaceae overgrowth. Video Abstract.

Complete genome sequence of one novel marine Pseudomonas sp. BSw22131 growing with dimethylsulfoniopropionate (DMSP) as the sole carbon source

Members of the genus Pseudomonas have been frequently isolated from the marine environment, indicating their ecological role in native habitats. One bacterial strain, Pseudomonas sp. BSw22131, was isolated from seawater in Kongsfjorden, Svalbard. The bacterium can grow with algae-derived dimethylsulfoniopropionate (DMSP) as the sole carbon source. Here, we sequenced the complete genome of strain BSw22131, which contained a single circular chromosome of 5,739,290 (G + C content of 58.23 mol%) without any plasmids. A total of 5362 protein-coding genes, 65 tRNA genes, and 16 rRNA genes were obtained. Genome sequence analysis revealed that strain BSw22131 was not only a potential novel species of the genus Pseudomonas but also different from Pseudomonas sp. DMSP-1 that was isolated from the same habitat and also utilized DMSP as the sole carbon source for growth. The results can be helpful for understanding the catabolism of the genus Pseudomonas in sulfur cycling in the Arctic fjord ecosystem.

Accelerating denitrification and mitigating nitrite accumulation by multiple electron transfer pathways between Shewanella oneidensis MR-1 and denitrifying microbial community

The bio-denitrification was usually retarded by the unbalance of electron generation and consumption. In this study, mixing S. oneidensis MR-1 with denitrifying microbial community increased the nitrogen removal rate by 74.74 % via the interspecies electron transfer (IET), and reduced the accumulated nitrite from 9.90 ± 0.81 to 0.02 ± 0.03 mg/L. Enhanced denitrification still appeared but relatively decreased, when S. oneidensis MR-1 was separated by a dialysis bag (MW < 3000), indicating mediated interspecies electron transfer (MIET) counted in IET. The results of electron transfer activity and sludge conductivity suggested DIET and MIET jointly transfer electrons from MR-1 to electroactive denitrifying bacteria (EDB), improving denitrifying reductase activities. Electron distribution among denitrifying reductases was found to be associated with the IET rate. Microbial insights showed the total abundance of EDB was increased, and denitrifying genes were correspondingly enriched. Pseudomonas was found to cooperate with exoelectrogens in a complicated microbial community.

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.

A novel algicidal bacteria isolated from native snail lived in Taihu Lake against algal blooms: identification, degradation kinetic, and algicidal mechanism

Harmful algal blooms (HABs) impacted negatively the water ecosystem, and produced toxic microcystins that poses toxic effect on liver, nervous, and genital system. The introduction of useful and adaptive algae-degrading microbes or bio-augmentation can be regarded as an efficient way to inhibit the outbreak of HABs. The purpose of this study is to evaluate the application potential of algicidal bacteria named XMC, which is isolated from native snails. Response surface methodology (RSM) experiments showed that self-characteristic and various external conditions affected the actual algae inhibition ability of XMC. In particular, actual algicidal efficiency was strongly depend on the temperature and growth stage of XMC, and the maximum algicidal rate could reach 93.95% within 7 days. The degradation curve of Microcystis aeruginosa was compliant with the first-order kinetic model, which could be used to predict the degradation effect of Microcystis aeruginosa in engineering applications. The analysis results of algae dissolution products showed that algicidal bacteria XMC had both direct and indirect algicidal capacity. In addition, XMC had strong algicidal ability and greater environmental adaptability, and its algae dissolution products were environmentally friendly. All results indicated that XMC had the potential to be used in the bio-degradation of cyanobacteria bloom.

Removal of harmful algae by Shigella sp. H3 and Alcaligenes sp. H5: algicidal pathways and characteristics

Application of algicidal bacteria is a promising technology to control harmful algal blooms (HABs). In this study, algicidal bacteria strains Shigella sp. H3 and Alcaligenes sp. H5 were obtained via two different isolation methods from the same lake water sample, with optimal algicidal efficiencies 96% and 74% against algae mixture. The Shigella sp. H3 and Alcaligenes sp. H5 lysed algae cells through cells-to-cells direct contact and secretion of algicidal metabolites, respectively. The stronger algicidal capability of Shigella sp. H3 was also attributable to its higher efficiency for triggering reactive oxygen species, which led to broken down of the antioxidant system and more severe damage to the bacterial cells. The antioxidant enzyme activities in Alcaligenes sp. H5 group were still expressed because of its relatively weaker algicidal capability and some intact algal cells were remained. The liquid carbohydrates from algal lysis in both groups increased significantly, whereas the quantities of liquid protein decreased, which might be assimilated by algicidal bacteria. Nonetheless, the whole algicidal process resulted in the increase of total released organic matters content. This study revealed the algicidal pathways of diverse bacterial strains, and the possible secondary environmental problem caused by the algal released organic matters should be considered when applying bacteria to control HABs.

Spatiotemporal changes of bacterial communities during a cyanobacterial bloom in a subtropical water source reservoir ecosystem in China

Cyanobacterial blooms, which not only threaten the health and stability of aquatic ecosystems but also influence the microbial community within, emerges as one of the most concerning problems in China. However, how cyanobacterial blooms affect the spatiotemporal variation of aquatic microbial communities remains relatively unclear. In this study, we used high-throughput sequencing to investigate how the cyanobacterial and bacterial community spatiotemporally vary along with main cyanobacterial bloom phases in upstream rivers of a eutrophicated water source reservoir. Both cyanobacterial and bacterial diversities in each river were significantly lower (P < 0.05) during the bloom outbreak phase, showing the apparent influence of cyanobacterial bloom. Dominant cyanobacterial taxa included Cyanobacteriales and Synechococcales, and dominant bacterial taxa comprised Acinetobacter, CL500-29, hgcI clade, Limnohabitans, Flavobacterium, Rhodoluna, Porphyrobacter, Rhodobacter, Pseudomonas, and Rhizobiales, whose changes of relative abundance along with the bloom indicated distinct community composition. Non-metric multidimensional scaling analysis proved that community composition had significant difference amongst bloom phases. Linear discriminant analysis (LDA) with LDA effect size analysis (LEfSe) identified unique dominant cyanobacterial and bacterial OTUs at different phases in each river, indicating spatiotemporal variations of communities. Canonical correlation analysis or redundancy analysis revealed that at different bloom phases communities of each river had distinct correlation patterns with the environmental parameters (temperature, ammonium, nitrate, and total phosphorus etc.), implying the spatial variations of microbial communities. Overall, these results expand current understanding on the spatiotemporal variations of microbial communities due to cyanobacterial blooms. Microbial interactions during the bloom may shed light on controlling cyanobacterial blooms in the similar aquatic ecosystems.

Genome Analysis of Enterobacter asburiae and Lelliottia spp. Proliferating in Oligotrophic Drinking Water Reservoirs and Lakes

Surface waters are one of the main sources for drinking water production, and thus microbial contamination should be as minimal as possible. However, high concentrations of coliform bacteria were detected in reservoirs and lakes used for drinking water production during summer months due to autochthonous proliferation processes. Here, we present the genomic analyses of 17 strains of Enterobacter asburiae and Lelliottia spp. proliferating in reservoirs and lakes with special focus on the hygienic relevance, antibiotic resistance, and adaptations to the oligotrophic environments. The genomes contain neither genes for the type III secretion system nor cytotoxins or hemolysins, which are considered typical virulence factors. Examination of antibiotic resistance genes revealed mainly efflux pumps and β-lactamase class C (ampC) genes. Phenotypically, single isolates of Enterobacter asburiae showed resistance to fosfomycin and ceftazidime. The genome analyses further suggest adaptations to oligotrophic and changing environmental conditions in reservoirs and lakes, e.g., genes to cope with low nitrate and phosphate levels and the ability to utilize substances released by algae, like amino acids, chitin, alginate, rhamnose, and fucose. This leads to the hypothesis that the proliferation of the coliform bacteria could occur at the end of summer due to algae die-off. IMPORTANCE Certain strains of coliform bacteria have been shown to proliferate in the oligotrophic water of drinking water reservoirs and lakes, reaching values above 10⁴ per 100 mL. Such high concentrations challenge drinking water treatment, and occasionally the respective coliform bacteria have been detected in the treated drinking water. Thus, the question of their hygienic relevance is of high importance for water suppliers and authorities. Our genomic analyses suggest that the strains are not hygienically relevant, as typical virulence factors are absent and antibiotic resistance genes in the genomes most likely are of natural origin. Furthermore, their presence in the water is not related to fecal contamination. The proliferation in reservoirs and lakes during stable summer stratification is an autochthonic process of certain E. asburiae and Lelliottia strains that are well adapted to the surrounding oligotrophic environment.

Enhanced wastewater treatment performance by understanding the interaction between algae and bacteria based on quorum sensing

In order to further obtain sustainable wastewater treatment technology, in-depth analysis based on algal-bacterial symbiosis, quorum sensing signal molecules and algal-bacterial relationship will lay the foundation for the synergistic algal-bacterial wastewater treatment process. The methods of enhancing algae and bacteria wastewater treatment technology were systematically explored, including promoting symbiosis, reducing algicidal behavior, eliminating the interference of quorum sensing inhibitor, and developing algae and bacteria granular sludge. These findings can provide guidance for sustainable economic and environmental development, and facilitate carbon emissions reduction by using algae and bacteria synergistic wastewater treatment technology in further attempts. The future work should be carried out in the following four aspects: (1) Screening of dominant microalgae and bacteria; (2) Coordination of stable (emerging) contaminants removal; (3) Utilization of algae to produce fertilizers and feed (additives), and (4) Constructing recombinant algae and bacteria for reducing carbon emissions and obtaining high value-added products.

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 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.

Prophylactic Addition of Glucose Suppresses Cyanobacterial Abundance in Lake Water

To mitigate harmful cyanobacterial blooms (HCBs), toxic algicides have been used, but alternative methods of HCB prevention are needed. Our goal was to test the prophylactic addition of glucose to inhibit HCB development, using Microcystis and the toxin microcystin as the HCB model. Water samples were collected weekly, from 4 June to 2 July, from Harsha Lake in southwestern Ohio during the 2021 algal bloom season. From each weekly sample, a 25 mL aliquot was frozen for a 16S rRNA gene sequencing analysis. Then, 200 mL of Harsha Lake water was added to each of the three culture flasks, and glucose was added to create concentrations of 0 mM (control), 1.39 mM, or 13.9 mM glucose, respectively. The microcystin concentration in each flask was measured after 1 and 2 weeks of incubation. The results showed an 80 to 90% reduction in microcystin concentrations in glucose-treated water compared to the control. At the end of the second week of incubation, a 25 mL sample was also obtained from each of the culture flasks for molecular analysis, including a 16S rRNA gene sequencing and qPCR-based quantification of Microcystis target genes. Based on these analyses, the glucose-treated water contained significantly lower Microcystis and microcystin producing gene (mcy) copy numbers than the control. The 16S rRNA sequencing analysis also revealed that Cyanobacteria and Proteobacteria were initially the most abundant bacterial phyla in the Harsha Lake water, but as the summer progressed, Cyanobacteria became the dominant phyla. However, in the glucose-treated water, the Cyanobacteria decreased and the Proteobacteria increased in weekly abundance compared to the control. This glucose-induced proteobacterial increase in abundance was driven primarily by increases in two distinct families of Proteobacteria: Devosiaceae and Rhizobiaceae. In conclusion, the prophylactic addition of glucose to Harsha Lake water samples reduced Cyanobacteria’s relative abundance, Microcystis numbers and microcystin concentrations and increased the relative abundance of Proteobacteria compared to the control.

Different Algicidal Modes of the Two Bacteria Aeromonas bestiarum HYD0802-MK36 and Pseudomonas syringae KACC10292T against Harmful Cyanobacteria Microcystis aeruginosa

Blooms of harmful cyanobacteria Microcystis aeruginosa lead to an adverse effect on freshwater ecosystems, and thus extensive studies on the control of this cyanobacteria’s blooms have been conducted. Throughout this study, we have found that the two bacteria Aeromonas bestiarum HYD0802-MK36 and Pseudomonas syringae KACC10292^T are capable of killing M. aeruginosa. Interestingly, these two bacteria showed different algicidal modes. Based on an algicidal range test using 15 algal species (target and non-target species), HYD0802-MK36 specifically attacked only target cyanobacteria M. aeruginosa, whereas the algicidal activity of KACC10292^T appeared in a relatively broad algicidal range. HYD0802-MK36, as a direct attacker, killed M. aeruginosa cells when direct cell (bacterium)-to-cell (cyanobacteria) contact happens. KACC10292^T, as an indirect attacker, released algicidal substance which is located in cytoplasm. Interestingly, algicidal activity of KACC10292^T was enhanced according to co-cultivation with the host cyanobacteria, suggesting that quantity of algicidal substance released from this bacterium might be increased via interaction with the host cyanobacteria.

A novel co-graft tannin-based flocculant for the mitigation of harmful algal blooms (HABs): The effect of charge density and molecular weight

In this study, for the first time, we developed a series of co-graft tannin-based flocculants, TA-g-P(AM-DMDAAC), with different charge densities (CDs) and molecular weights (MWs) and evaluated their algal-removal performances. The effects of TA-g-P(AM-DMDAAC) on the cell integrity of Microcystis aeruginosa and release of extracellular organic matter (EOM) and microcystin-leucine-arginine (MC-LR) in flocculation and floc storage were also studied. Results suggested that TA-g-P(AM-DMDAAC) could not only efficiently remove algal cells over a wide pH range (pH 3-11) but also EOM. CD and MW significantly affected flocculation performance and floc characteristics of TA-g-P(AM-DMDAAC). A higher CD helped achieve a higher removal efficiency of algal cells and EOM, whereas a higher MW resulted in the formation of larger and more compact flocs. Furthermore, the larger and denser flocs could better protect algal cells and reduce the release of EOM during floc storage. Notably, algal cells in the TA-g-P(AM-DMDAAC) flocs did not appear to show signs of massive rupture nor did they release EOM and MC-LR extensively for at least 20 days of storage. The abundance and easy availability of tannin resources effectively reduce the cost of preparing tannin-based flocculants. Therefore, TA-g-P(AM-DMDAAC) can have broad application prospects in the management of cyanobacteria bloom.

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.

The algicidal efficacy and the mechanism of Enterobacter sp. EA-1 on Oscillatoria dominating in aquaculture system

The global escalation and intensification of cyanobacterial blooms require powerful algaecides. This study investigated the algicidal efficacy and mechanism of EA-1 against Oscillatoria. Bacteria EA-1, identified as Enterobacter, was isolated with high algicidal activity against harmful cyanobacteria. Results showed that a complete removal of Oscillatoria was observed within 3 days with the initial Chl-a concentration of 1.74 mg/L. Physiological responses of Oscillatoria revealed that EA-1 induced severe lipid peroxidation and the ultimate decline of antioxidant enzyme activities. Moreover, the contents for both intracellular protein and carbohydrate of each algae cell increased first and then decreased. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) analysis clarified that the possible process of Oscillatoria lysis included the breach of cross wall, followed by the disruption of photosynthetic membrane and incipient nucleus, and the ultimate outflow of inclusion. Confocal laser scanning microscopy (CLSM) analysis illustrated the degradation process of incipient nucleus in Oscillatoria.

Diatoms recovery from wastewater: Overview from an ecological and economic perspective

Alarming water pollution is toxic to the aquatic ecosystem leading to a sharp decline in species diversity. Diatoms have great potency to survive in contaminated water bodies, hence they can be compelling bioindicators to monitor the change in the environmental matrices effectively. Around the globe, researchers are intended to evaluate the impact of pollution on the diatoms recovery and techniques used for the assessment. The diatoms are precious for futuristic need viz. value-added products, energy generation, pharmaceuticals, and aquaculture feedstocks. All these applications led to a significant rise in diatoms research among the scientific community. This review presents different isolation practices, cultivation, and other challenges associated with the diatoms. A precise focus is given to diatoms isolation techniques from highly polluted water bodies with the main thrust towards obtaining an axenic culture to elucidate the significance of pure diatom cultures. Recovery of "jewels of the sea" from polluted water signifies the prospective ecological and economic aspects.