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The blue-green microalgae Arthrospira was firstly introduced in Vietnam in the 1970s. Until now, the production of Arthrospira is still far from meeting the growing demand for dietary supplements, feeds, and biofertilizers. It was a paradox that most Arthrospira production plants located in the Northern provinces were characterized by cold winter with a temperature of about 10–15°C while only a few production plants in the South where the climate was favourable for large-scale production year around. Therefore, it is necessary to have better strategies and suitable techniques to increase productivity and yield. Based on the data obtained from the investigation, the production areas of Arthrospira should be set up in the South rather than in the Northern regions to take advantage of the natural condition for better yield. This paper outlines the history, current situation, and prospects of Arthrospira production in Vietnam.

Four thymol derivatives and two phenolic compounds were isolated from the aerial parts of Eupatorium fortunei. The new structures were elucidated to be 7,8,9-trihydroxythymol (1), and 8,10-didehydro-7,9-dihydroxythymol (2) by means of MS and NMR analysis. The known compounds were identified as 8,9,10-trihydroxythymol (3), 10-acetoxy-8,9-dihydroxythymol (4), o-coumaric acid (5) and 4-(2-hydroxyethyl)benzaldehyde (6). Compound 3 showed strongest inhibitory effect on the growth of Microcystis aeruginosa in comparison with CuSO4.

The occurrence of increasing blooms of toxic cyanobacteria in freshwaters has received much attention due to the ability of many cyanobacteria to produce potent cyanotoxins. In this paper, the occurrence of dominant cyanobacteria and the concentration of microcystins (MCs) analysis were investigated monthly from July 2008 to April 2009 in the Hoan Kiem Lake and from February to April 2009 in the Nui Coc reservoir. Concentrations of intracellular MCs from water, bloom samples, and isolated strains were quantified by using high performance liquid chromatography (HPLC). During the study period, the microscopic examination of the phytoplankton samples showed the dominance of the genus Microcystis in the water environment of the Hoan Kiem Lake and the Nui Coc reservoir. The toxin analysis by HPLC demonstrated the presence of two MC variants: MC-LR and MC-RR in water samples. Total concentrations of the toxins in filtered samples from surface water ranged from non-detected to 0.91 μg L−1 at Nui Coc reservoir and they ranged from 2.1 to 46.0 μg L−1 at Hoan Kiem Lake. The results of the HPLC analysis confirmed the production of MCs in bloom samples (ranged from 115.9 to 184.6 μg L−1 in the Hoan Kiem Lake and from 726.5 to 1116 μg L−1 in the Nui Coc reservoir) and isolated strains of Anabaena sp. and Microcystis with the concentration of MC ranging from 152 to 396.2 μg g−1 dry mass, respectively.

In order to understand the environmental varia- bles which promote the proliferation of cyanobacteria and variation in microcystin concentrations in the Nui Coc res- ervoir, Vietnam, physicochemical parameters, the occur- rence, and abundance of phytoplankton, cyanobacteria, and microcystin concentration were monitored monthly through the year 2009-2010. The relationships between these parameters were explored using principal component analysis (PCA) and Pearson correlation analysis. The phy- toplankton community was mainly dominated by the cya- nobacterium Microcystis with higher cyanobacteria abundance during summer and autumn season. PCA and Pearson correlation results showed that water temperature and phosphate concentration were the most important vari- ables accounting for cyanobacteria, Microcystis, and micro- cystin occurrence. Analysis of the toxins by high- performance liquid chromatography demonstrated the pres- ence of two microcystin variants: microcystin-LR (MC-RR) and microcystin-ddRR (MC-ddRR) with total concentra- tions of the toxins in filtered samples from surface water ranging from 0.11 to 1.52 μg MC-LR equiv L �1 . The high concentrations of microcystin in the Nui Coc reservoir high- lighted the potential risk for human health in the basin. Our study underlined the need for regular monitoring of cyano- bacteria and toxins in lakes and reservoirs, which are used for drinking water supplies, not only in Vietnam but also in tropical countries.

Several Vietnamese freshwater cyanobacteria were collected and evaluated for their effects on the transcriptional nuclear factor κB (NF-κB) which are involving in the cancer and inflammatory diseases. Five extraction conditions were tested and a solution of 2% acetic acid in methanol provided highest yield of extract from bacterial biomass. The Microcystis aeruginosa TC-1 and TC-3 strains showed strong NF-κB inhibitory activity with IC50 values of 6.1 and 5.3 μg/ml, respectively. Moreover, all tested cyanobacteria exhibited cytotoxicity on human cervical cancer HeLa cells in a dose-dependent manner. Ergosterol (1) isolated from M. aeruginosa TC-3 strains strongly inhibited NF-κB activation with IC50 values of 0.91 μg/ml.

Periphytic diatom communities’ colonization patterns were studied at three sampling stations of the Red–Nhue–Tolich hydrosystem presenting different urban pollution levels by using artificial substrates for 6 weeks in dry season 2005. Structural characteristics of periphytic diatoms developed on glass substrates at each sampling site were followed and compared. This experiment showed, through various general criteria (total diatom density, dry weight biomass) and specific criteria (relative diatom abundances, indices) that the structure of benthic diatoms developed on these substrates was strongly affected by pollution as early as the second week of colonization. Communities exposed to heavily and moderately polluted sites contained species which are known to be saprophilous or tolerant to organic pollution such as Nitzschia umbonata , Nitzschia palea , Cyclotella meneghiniana , Eolimna minima . Growth inhibition of diatom communities at the heavily polluted site was mostly related to a strong increase of organic load rather than to low metallic input, though metallic (Cd and Zn) burdens have been successfully quantified in the biofilms developed at the three studied sites. Nevertheless, no significant difference in species richness and diversity index between colonization duration times was observed. Based on values of diatom indices Indice de Polluosensibilite (IPS) and diatom assemblage index to organic water pollution (DAIPo), water quality could be classified as medium quality at Red site, polluted at NT 2 and heavily polluted at TL. Thus, the use of diatoms as a tool for water assessment appears suitable for monitoring rivers in Vietnam, as it is in several other countries.

The effects of urban pollution from Hanoi city on the benthic diatom communities of the Nhue–Tolich river system were studied during the 2003 dry season. Benthic diatoms were allowed to grow on glass slides suspended in the water flow for 4 weeks. To reveal the relationship between water quality and diatom communities, Canonical correspondence analysis (CCA) was used on data concerning relative abundances of diatom species and environmental variables. Two diatom indices, IPS and DAIpo, were applied to evaluate water quality in the three rivers. A total of 291 diatom taxa were found in the Red, Nhue and Tolich Rivers. These were mainly cosmopolitan taxa, with some tropical, subtropical and endemic taxa. The most abundant taxa at the Red site were Aulacoseira granulata, Achnanthidium minutissimum, Encyonema minutum, Navicula recens and other halophilous taxa such as Nitzschia kurzii, Seminavis strigosa, Entomoneis paludosa, Bacillaria paradoxa. Diatom assemblages at the Tolich site consisted mainly of Nitzschia umbonata, Nitzschia palea and Eolimna minima. Diatom density ranged from 660 to 30,000 cells/cm2. Environmental variables and diatom assemblage composition at all sites were significantly correlated. Two diatom indices gave similar results and indicate the Tolich River with the lowest values as a highly polluted site.

International audience; Field transfer experiments of periphytic diatom assemblages developed on artificial substrates were set up to assess the responses of those communities to environmental disturbances. The glass slides were positioned for colonization at the relatively unpolluted site (Red, in the Red River) and at the heavily polluted site (TL, in the To Lich River) in the beginning of the experiment. After a period of 2 weeks, the colonized glass slides were concomitantly transferred from the unpolluted Red site to the heavily polluted TL site and to the moderate polluted site (NT 2, in the Nhue River) and, conversely, from the TL site to the Red site, and then to the NT 2 site. The responses and the adapting capacity of periphytic diatom communities to environmental changes were assessed through the cell density, diversity index, species richness, taxonomic composition, and diatom indices after 2 and 4 weeks of transfer periods. For all transfers except for the transfer from the Red to the TL site in which the growth inhibition of diatom cells was found, the diatom density significantly increased until the end of the experiment. Thus, the diatom communities have expressed their pollution tolerance or sensitivities by changing their composition to adapt themselves to environmental changes. Characteristic species of the Red site (Gyrosigma scalproides, Navicula recens) were replaced by Nitzschia palea, Nitzschia umbonata, Aulacoseira granulate typical species of the NT 2 site, in the biofilm transferred from the Red site to the NT 2 site. The relative abundances of typical diatom species of the Red site proliferated in the biofilm transferred from the TL site to the Red site. The replacement of periphytic diatom communities appeared after the transfer from the second week at the different sites. The slow shift of the species towards the typical species at the TL site could result from the organized structure of diatoms within biofilm before the transfer from the Red site to the TL site. The shifts in values of the Index of Specific Polluosensitivity and Diatom Assemblage Index to organic pollution throughout the experiment indicated the clear sensitivity of these indices to water quality changes.