Effects of different cultivation conditions on the production of ß-cyclocitral and ß-ionone in Microcystis aeruginosa.

BACKGROUND: Cyanobacteria blooms have become a major environmental problem and concern because of secondary metabolites produced by cyanobacteria released into the water. Cyanobacteria produce volatile organic compounds (VOCs), such as the compounds ß-cyclocitral and ß-ionone, which comprise odors, off-flavors, defense compounds, as well as growth regulators. Therefore, the general objective of this work was to evaluate the VOCs produced by two strains of Microcystis aeruginosa, differing in their ability to produce microcystins (LTPNA 01-non-producing and LTPNA 08-toxin-producing). The analysis of VOC production was carried out in (1) normal culture conditions, (2) under different light intensities (LI), and (3) after the external application of ß-ionone in both cultures. RESULTS: The results showed that ß-cyclocitral and ß-ionone are produced in all growth phases of LTPNA 01 and LTPNA 08. Both strains were producers of ß-cyclocitral and ß-ionone in normal culture conditions. It was observed that the ß-cyclocitral concentration was higher than ß-ionone in all light intensities investigated in this study. Additionally, the strain LTPNA 01 produced more ß-cyclocitral than LTPNA 08 at almost all times and LIs analyzed. However, the strain LTPNA 08 produced more ß-ionone, mainly at the initial times. In addition, the experiment results with the external addition of ß-ionone in the cultures showed that the strain LTPNA 01 produced more ß-cyclocitral in control conditions than in treatment. Nonetheless, ß-ionone production was higher in treatment conditions in LTPNA 08, indicating that the addition of ß-ionone may favor the production of these compounds and inhibit the production of ß-cyclocitral. CONCLUSION: Our results showed that some abiotic factors, such as different light intensities and external application of ß-ionone, can be triggers that lead to the production of VOCs.

Cyanotoxins and water quality parameters as risk assessment indicators for aquatic life in reservoirs.

We assessed the extent of pollution in an essential public water supply reservoir (southeastern Brazil). An environmental monitoring study was performed at the Billings Reservoir (at the water catchment site) to assess the water quality in 2017, 2018, and 2019. Physicochemical parameters were analyzed, quantifying the total cyanobacteria and the cyanotoxins microcystins (MCs) and saxitoxins (SXTs), as well as their possible ecological risk to the aquatic environment. We also determined metals and metalloids (As, Ba, Cd, Pb, Cu, Cr, Fe, Mn, Ni, Zn, and Sb) and fecal bacteria (Escherichia coli). Monthly samplings were performed for 2017, 2018, and 2019 (totaling 36 sampling campaigns). Metals, metalloids, and E. coli values were below the maximum limit allowed by the Brazilian legislation. High concentrations of total cyanobacteria (3.07 × 104 - 3.23 × 105 cells/mL), microcystin variants MC-LR (0.67-23.63 µg/L), MC-LA (0.03-8.66 µg/L), MC-RR (0.56-7.92 µg/L), and MC-YR (0.04-1.24 µg/L), as well as the saxitoxins GTX2 (0.18-5.37 µg/L), GTX3 (0.13-4.40 µg/L), and STX (0.12-2.92 µg/L) were detected. From an ecotoxicological point of view, the estimated values for the risk quotient (RQ) for microcystins and saxitoxins were largely greater than 1, indicating a high risk to aquatic life. Therefore, further efforts need to be made to delay the eutrophication of the reservoir.

Responses of Aquatic Nontarget Organisms in Experiments Simulating a Scenario of Contamination by Imidacloprid in a Freshwater Environment.

Several studies have indicated the presence of the neonicotinoid insecticide imidacloprid (IMI) in aquatic ecosystems in concentrations up to 320.0 µg L-1. In the present study, we evaluated the effects of the highest IMI concentration detected in surface water (320.0 µg L-1) on the survival of Chironomus sancticaroli, Daphnia similis, and Danio rerio in three different scenarios of water contamination. The enzymatic activities of glutathione S-transferase (GST), catalase (CAT), and ascorbate peroxidase (APX) in D. rerio also were determined. For this evaluation, we have simulated a lotic environment using an indoor system of artificial channels developed for the present study. In this system, three scenarios of contamination by IMI (320.0 µg L-1) were reproduced: one using reconstituted water (RW) and the other two using water samples collected in unpolluted (UW) and polluted (DW) areas of a river. The results indicated that the tested concentration was not able to cause mortality in D. similis and D. rerio in any proposed treatment (RW, UW, and DW). However, C. sancticaroli showed 100% of mortality in the presence of IMI in the three proposed treatments, demonstrating its potential to impact the community of aquatic nontarget insects negatively. Low IMI concentrations did not offer risks to D. rerio survival. However, we observed alterations in GST, CAT, and APX activities in treatments that used IMI and water with no evidence of pollution (i.e., RW and UW). These last results demonstrated that fish are more susceptible to the effects of IMI in unpolluted environments.

Inhibition of Porcine Aminopeptidase M (pAMP) by the Pentapeptide Microginins.

Aminopeptidase M (AMP) inhibition is of interest for several diseases, such as highly vascularized cancer types. AMP can be inhibited by linear pentapeptides isolated from Microcystis aeruginosa LTPNA08 (MG7XX). Porcine AMP inhibition-a model for human AMP-activity was spectrophotometrically measured by the formation of p-nitroanilide from L-leucine-p-nitroanilide substrate by AMP. AMP inhibition by MG770 exhibited comparable inhibition levels to amastatin (IC50 values: 1.20 ± 0.1 µM and 0.98 ± 0.1 µM, respectively), while MG756 was slightly less potent (with IC50 values of 3.26 ± 0.5 µM). Molecular modelling suggests a potential binding mode, based on the interaction with the Zn2+ cofactor, where MG770's extra methyl group contributes to the disturbance of the Zn2+ cofactor complex and highlights the importance of hydrophobicity for the site.

'Floc and Sink' Technique Removes Cyanobacteria and Microcystins from Tropical Reservoir Water.

Combining coagulants with ballast (natural soil or modified clay) to remove cyanobacteria from the water column is a promising tool to mitigate nuisance blooms. Nevertheless, the possible effects of this technique on different toxin-producing cyanobacteria species have not been thoroughly investigated. This laboratory study evaluated the potential effects of the "Floc and Sink" technique on releasing microcystins (MC) from the precipitated biomass. A combined treatment of polyaluminium chloride (PAC) with lanthanum modified bentonite (LMB) and/or local red soil (LRS) was applied to the bloom material (mainly Dolichospermum circinalis and Microcystis aeruginosa) of a tropical reservoir. Intra and extracellular MC and biomass removal were evaluated. PAC alone was not efficient to remove the biomass, while PAC + LMB + LRS was the most efficient and removed 4.3-7.5 times more biomass than other treatments. Intracellular MC concentrations ranged between 12 and 2.180 µg L-1 independent from the biomass. PAC treatment increased extracellular MC concentrations from 3.5 to 6 times. However, when combined with ballast, extracellular MC was up to 4.2 times lower in the top of the test tubes. Nevertheless, PAC + LRS and PAC + LMB + LRS treatments showed extracellular MC concentration eight times higher than controls in the bottom. Our results showed that Floc and Sink appears to be more promising in removing cyanobacteria and extracellular MC from the water column than a sole coagulant (PAC).