Encapsulation and Algicidal Properties of Fermentation Products From Vibrio brasiliensis H115

Algicidal bacteria offer an eco-friendly and promising approach for controlling harmful algae blooms (HABs). In this study, repeated batch fermentation of immobilized algicidal bacterium Vibrio brasiliensis H115 was preformed to enhance the productivity of the algicidal compounds. The highest algicidal efficiency of the fermentation products against Akashiwo sanguinea (100%) was achieved when the fermentation time was decreased from 24 to 14 h. The cell-free fermentation broth was then spray-dried and floating microcapsules were prepared from the dried powder. The optimum preparation conditions for floating microcapsules were: sodium alginate (SA), 3%; CaCO3: SA (mass ratio), 3:4; CaCl2, 3%; citric acid, 4%; ethylcellulose, 2%; crosslinking time, 30 min. Under the optimal conditions, the floating microcapsules displayed efficient A. sanguinea cell lysis ability and the algicidal efficiency increased from 10.62% (4 h) to 100% (24 h). These results suggest that the floating microcapsules could potentially be practically used for controlling the outbreaks of A. sanguinea.

The Roseobacter-group bacterium Phaeobacter as safe probiotic solution for aquaculture

Phaeobacter inhibens has been assessed as a probiotic bacterium for application in aquaculture. Studies addressing the efficacy and safety indicate that P. inhibens maintains it antagonistic activity against pathogenic vibrios in aquaculture live cultures (live feed and fish egg/larvae), while having no or a positive effect on the host organisms, and a minor impact on the host microbiomes. While producing antibacterial and algicidal compounds, no study has so far found a virulent phenotype of P. inhibens cells against higher organisms. Additionally, an in silico search for antibiotic resistance genes using published genomes of representative strains did not raise concern regarding the risk for antimicrobial resistance. P. inhibens occurs naturally in aquaculture systems supporting its safe usage in this environment. Concluding, at the current state of knowledge, P. inhibens is a “safe-to-use” organism.

Questiomycins, Algicidal Compounds Produced by the Marine Bacterium Alteromonas sp. D and Their Production Cue

Questiomycin A (1) along with three new compounds, questiomycins C–E (2–4), were isolated from culture of Alteromonas sp. D, an algicidal marine bacterium, guided by algal lethality assay using the raphidophyte, Chattonella antiqua, one of the causative organisms of harmful algal bloom. The structures of 1–4 were assigned on the basis of their spectrometric and spectroscopic data. Compounds 1 to 4 exhibited algicidal activity against C. antiqua with LC50 values ranging from 0.18 to 6.37 M. Co-cultivation experiment revealed that 1 was produced only when the microalgae and the bacterium are in close contact, suggesting that some interactions between them trigger the biosynthesis of questiomycins. These results suggested that the algicidal bacteria such as Alteromonas sp. D can control microalgae chemically in marine ecosystem.

Combined treatment of toxic cyanobacteria Microcystis aeruginosa with hydrogen peroxide and microcystin biodegradation agents results in quick toxins elimination

In some conditions the growth of toxic cyanobacteria must be controlled by treatment with algicidal compounds. Hydrogen peroxide has been proposed as an efficient and relatively safe chemical which can remove cyanobacteria from the environment selectively, without affecting other microorganisms. However, the uncontrolled release of secondary metabolites, including toxins may occur after such a treatment. Our proposal presented in this paper is fast biodegradation of microcystin released after cell lysis induced by hydrogen peroxide. The effectiveness of both Sphingomonas sp. and heterologously expressed MlrA enzyme in the removal of the toxin from Microcystis aeruginosa culture has been investigated. The results indicate that neither Sphingomonas cells nor MlrA are affected by hydrogen peroxide in the concentrations which stop the growth of cyanobacteria. A several-fold microcystin reduction was documented in the presence of these agents with biodegradation ability. Our results provide evidence that such a combined treatment of water reservoirs dominated by microcystin-producing cyanobacteria may be a promising alternative which allows fast elimination of toxins from the environment.

Algicidal Activity of Streptomyces eurocidicus JXJ-0089 Metabolites and Their Effects on Microcystis Physiology

ABSTRACTCopper sulfate (CuSO4) has been widely used as an algicide to control harmful cyanobacterial blooms (CyanoHABs) in freshwater lakes. However, there are increasing concerns about this application, due mainly to the general toxicity of CuSO4to other aquatic species and its long-term persistence in the environment. This study reported the isolation and characterization of two natural algicidal compounds, i.e., tryptamine and tryptoline, fromStreptomyceseurocidicusJXJ-0089. At a concentration of 5 μg/ml, both compounds showed higher algicidal efficiencies than CuSO4onMicrocystissp. FACHB-905 and some other harmful cyanobacterial strains. Tryptamine and tryptoline treatments induced a degradation of chlorophyll and cell walls of cyanobacteria. These two compounds also significantly increased the intracellular oxidant content, i.e., superoxide anion radical (O2−) and malondialdehyde (MDA), but reduced the activity of intracellular reductants, i.e., superoxide dismutase (SOD), of cyanobacteria. Moreover, tryptamine and tryptoline treatments significantly altered the internal and external contents of microcystin-LR (MC-LR), a common cyanotoxin. Like CuSO4, tryptamine and tryptoline led to releases of intracellular MC-LR fromMicrocystis, but with lower rates than CuSO4. Tryptamine and tryptoline (5 μg/ml) in cyanobacterial cultures were completely degraded within 8 days, while CuSO4persisted for months. Overall, our results suggest that tryptamine and tryptoline could potentially serve as more efficient and environmentally friendly alternative algicides than CuSO4in controlling harmful cyanobacterial blooms.IMPORTANCECyanobacterial harmful algal blooms (CyanoHABs) in aquatic environments have become a worldwide problem. Numerous efforts have been made to seek means to prevent, control, and mitigate CyanoHABs. Copper sulfate (CuSO4), was once a common algicide to treat and control CyanoHABs. However, its application has become limited due to concerns about its general toxicity to other aquatic species and its long-term persistence in the environment. There is a great need for algicides with higher specificity and low environmental impacts. This study reports the isolation and characterization of two natural algicidal compounds from a streptomycete strain,Streptomyces eurocidicusJXJ-0089. Our results suggest that the identified algicides could potentially serve as more efficient and environmentally friendly alternative algicides than CuSO4in controlling harmful cyanobacterial blooms.