Algicidal activity of Aeromonas hydrophila sdPS-7 isolate against toxic marine dinoflagellate Alexandrium minutum KB- 5

Aims: Several harmful dinoflagellate species are widely found in Malaysian marine waters. These microalgae are capable of producing a variety of toxins that can intoxicate humans through consumption of contaminated seafood. Therefore, the present work aimed to investigate the potential of a marine bacterium sdPS-7 isolate as a biological control agent against Alexandrium minutum KB-5. Methodology and results: The isolate sdPS-7 was obtained from marine sediments in Malaysia and examined for its algicidal activity toward the toxic dinoflagellate A. minutum KB-5 in laboratory culture. Based on morphological and molecular characterization, this isolate was identified as Aeromonas hydrophila sdPS-7. Alexandrium minutum KB-5 cultures were exposed to cell free bacteria culture filtrate and the effect on dinoflagelate growth was evaluated based on direct cell counts in the treated samples compared to non-treated control cultures. The bacterial filtrate was treated at different temperatures, salinities and exposed to repeated freezing and thawing five times to study its algicidal activity stability thereafter. The results showed a potent inhibition of the growth of A. minutum KB-5. The strongest effect was observed when the bacterium culture filtrate was mixed with A. minutum KB-5 cultures that were in lag phase, resulting in 99% or higher mortality. The cell-free filtrate proved to be heat- stable when exposed to temperatures of 2 °C to 100 °C for one hour each. There was also no substantial salinity as well as (freezing – thawing) effect on the filtrate algicidal activity. Conclusion, significance and impact of study: This study illustrated the potential use of the marine bacterial Aeromonas hydrophila sdPS-7 filtrates in controlling the growth of the toxic dinoflagellate A. minutum KB-5.

Evaluation of the Antioxidant and Antimicrobial Properties of Nostoc Linckia Isolated from Kukkarahalli Lake, Mysore.

The present study evaluates the antioxidant and antimicrobial activity of Nostoc linckia which was isolated from Kukkarahalli lake, Mysore and maintained in BG-12 medium. The antioxidant potential of the N. linckia extract was investigated using 2,2- Diphenyl, 1- Picryl Hydrazyl and 2, 2´- Azino- bis-(3- ethylbenzothiazoline- 6- sulfonic acid) radical scavenging assays and ferric reducing power assay. It expressed DPPH radical scavenging activity at 1.58 mMTrolox Equivalent/g extract, ABTS˙ radical scavenging activity at 3.8 mMTE/g extract and total ferric reducing power at 1.05mgButylated Hydroxy Anisole Equivalents/ g extract. The radical scavenging activity was compared with BHA as standard wherein it expressed DPPH and ABTS˙+ radical scavenging activity of 2.8 mMTE/g and 4.3 mMTE/g respectively. In vitro bactericidal screening of ethanol extract of Nostoc linckia was carried out against six species of bacteria namely Bacillus cereus, Bacillus subtilis, Escherichia coli, Klebsiella oxytoca, Proteus vulgaris and Staphylococcus aureus wherein B. cereus, B. subtilis and E.coli expressed minimum bactericidal concentration values more than 1 mg/ml while K. oxytoca, P. vulgaris and S. aureus expressed MBC values of 0.51, 0.77 and 0.79 mg/ml respectiviely. The study also revealed minimum algicidal concentration of the extract at 0.625 mg/ml against Nostoc sp., Spirullina sp. Synecocystis sp., and 1.25 mg/ml against Gleocapsia sp by the 6th day after inoculation. The antimicrobial assay was carried out using micro titre plate method.

Isolation and characterization of an algicidal bacterium indigenous to lake Taihu with a red pigment able to lyse microcystis aeruginosa / 生物医学与环境科学（英文）

<p><b>OBJECTIVE</b>To isolate and characterize indigenous algicidal bacteria and their algae-lysing compounds active against Microcystis aeruginosa, strains TH1, TH2, and FACHB 905.</p><p><b>METHODS</b>The bacteria were identified using the Biolog automated microbial identification system and 16S rDNA sequence analysis. The algae-lysing compounds were isolated and purified by silica gel column chromatography and reverse-phase high performance liquid chromatography. Their structures were confirmed by Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FT-IR) spectroscopy. Algae-lysing activity was observed using microscopy.</p><p><b>RESULTS</b>The algae-lysing bacterium LTH-2 isolated from Lake Taihu was identified as Serratia marcescens. Strain LTH-2 secreted a red pigment identified as prodigiosin (C20H25N3O), which showed strong lytic activity with algal strains M. aeruginosa TH1, TH2, and FACHB 905 in a concentration-dependent manner. The 50% inhibitory concentration (IC50) of prodigiosin with the algal strains was 4.8 (± 0.4)× 10⁻² μg/mL, 8.9 (± 1.1)× 10⁻² μg/mL, and 1.7 (± 0.1)× 10⁻¹ μg/mL in 24 h, respectively.</p><p><b>CONCLUSION</b>The bacterium LTH-2 and its pigment had strong Microcystis-lysing activity probably related to damage of cell membranes. The bacterium LTH-2 and its red pigment are potentially useful for regulating blooms of harmful M. aeruginosa.</p>

Enrichment and Molecular Characterization of a Bacterial Culture Involved in Lysis of Microcystis aeruginosa / 微生物学通报

An enrichment culture showing specific algae-lysing activity was isolated from the mixtures of different samples and Microcystis aeruginosa. The process of algal lysis was monitored by chlorophyll measurement, PCR, and denaturing gradient gel electrophoresis (DGGE). The result showed that the enrichment culture had still high algicidal activity against M. aeruginosa after 1/100000 dilution. Rubritepida sp. C1, Pseudomonas sp. C2 and Sphingomonas sp. C3, as accompanying bacteria, existed in M.aeruginosa. The bacterial community in M. aeruginosa showed significant change after adding the enrichment culture, where uncultured Flavorbacterium sp. A2, Sphingomonas sp. C3 and Hydrogenophaga sp. A3 were observed, and A2 became a dominant species. The obvious correlation can be seen between change of bacterial population and extinction of M. aeruginosa. Compared identification of pure bacterium with sequencing of DGGE band, it was inferred that uncultured bacteria were probably play an important role in controlling the growth and abundance of M. aeruginosa.

ADVANCES ON ALGICIDAL SUBSTANCES PRODUCED BY ALGICIDAL BACTERIA / 微生物学通报

In recent years,more and more researchers have realized the possibility that algicidal bacteria could be a useful tool in reducing the impact of harmful algae blooms. In this review, the ecological roles of algicidal substances was briefly discussed, then special emphasis placed on the categories and extract methods of algicidal substances which have been reported. Some ideas for the further studies on algicidal substances were also proposed.