Generation of reactive oxygen species undergoing redox cycle of nostocine A: a cytotoxic violet pigment produced by freshwater cyanobacterium Nostoc spongiaeforme

Generation of Reactive Oxygen Species (ROS) by Harmful Algal Bloom (HAB)-Forming Phytoplankton and Their Potential Impact on Surrounding Living Organisms

Most marine phytoplankton with relatively high ROS generation rates are categorized as harmful algal bloom (HAB)-forming species, among which Chattonella genera is the highest ROS-producing phytoplankton. In this review, we examined marine microalgae with ROS-producing activities, with focus on Chattonella genera. Several studies suggest that Chattonella produces superoxide via the activities of an enzyme similar to NADPH oxidase located on glycocalyx, a cell surface structure, while hydrogen peroxide is generated inside the cell by different pathways. Additionally, hydroxyl radical has been detected in Chattonella cell suspension. By the physical stimulation, such as passing through between the gill lamellas of fish, the glycocalyx is easily discharged from the flagellate cells and attached on the gill surface, where ROS are continuously produced, which might cause gill tissue damage and fish death. Comparative studies using several strains of Chattonella showed that ROS production rate and ichthyotoxicity of Chattonella is well correlated. Furthermore, significant levels of ROS have been reported in other raphidophytes and dinoflagellates, such as Cochlodinium polykrikoides and Karenia mikimotoi. Chattonella is the most extensively studied phytoplankton in terms of ROS production and its biological functions. Therefore, this review examined the potential ecophysiological roles of extracellular ROS production by marine microalgae in aquatic environment.

Structure Simplification of Natural Products as a Lead Generation Approach in Agrochemical Discovery

Natural products (NPs) have a long history as sources of compounds for crop protection. Perhaps a more important role for NPs has been as models and inspiration for the discovery and development of synthetic crop protection compounds. NPs and their synthetic mimics account for 18% of all crop protection compounds, whereas another 38% of all crop protection compounds have a NP that could have served as a model. Because NPs are often complex molecules, have limited availability, or possess structural features that constrain their suitability for use in agricultural settings, a key element in NP-inspired compounds is the simplification of the NP structure to provide a synthetically accessible molecule that possesses the physicochemical properties needed for use in crop protection. Herein we review a series of examples of NP mimics that demonstrate the structural or synthetic simplification of NPs as a guide for the discovery of future NP-inspired agrochemicals focused on fungicides, herbicides, and insecticides.

Oxidative stress measurement in different morphological forms of wild-type and mutant cyanobacterial strains: Overcoming the limitation of fluorescence microscope-based method

Monitoring of oxidative stress caused by a wide range of reactive oxygen species (ROS) is essential to have an idea about the fitness and growth of photosynthetic organisms. The imaging-based oxidative stress measurement in cyanobacteria using 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) dye has the limitation of small sample size as the only selected number of cells are analyzed to measure the ROS levels. Here, we developed a method for oxidative stress measurement by DCFH-DA and flow cytometer (FCM) using unicellular Synechococcus elongatus PCC 7942 and filamentous Fremyella diplosiphon BK14 cyanobacteria. F. diplosiphon BK14 inherently possess high levels of ROS and showed higher sensitivity to hydrogen peroxide treatment in comparison to S. elongatus PCC 7942. We successfully measured oxidative stress in glutaredoxin lacking strain (Δgrx3) of S. elongatus PCC 7942, and wild-type Synechocystis sp. PCC 6803 using FCM based method. Importantly, ROS were not detected in these two strains of cyanobacteria by fluorescence microscope-based method due to their small spherical morphology. Δgrx3 strain showed high ROS levels in comparison to its wild-type strain. Treatment of abiotic factors such as high PAR in wild-type and Δgrx3 strains of S. elongatus PCC 7942, low PAR or low PAR + UVR in wild-type S. elongatus PCC 7942, and high PAR or high PAR + NaCl in Synechocystis sp. PCC 6803 increased oxidative stress. In summary, the FCM based method can measure ROS levels produced due to physiological conditions associated with genetic changes or abiotic stress in a large population of cells regardless of their morphology. Therefore, the present study shows the usefulness of the method in monitoring the health of organisms in a large scale cultivation system.

Cross talk: Two way allelopathic interactions between toxic Microcystis and Daphnia

Due to eutrophication, freshwater ecosystems frequently experience cyanobacterial blooms, many of which produce bioactive metabolites that can affect vertebrates and invertebrates life traits. Zooplankton are able to develop tolerance as a physiological response to cyanobacteria and their bioactive compounds, however, this comes with energetic cost that in turn influence Daphnia life traits and may impair populations. Vice versa, it has been suggested that Daphnia are able to reduce cyanobacterial dominance until a certain cyanobacterial density; it remains unclear whether Daphnia metabolites alone influence the physiological state and bioactive metabolites production of cyanobacteria. Hence, this study investigates mutual physiological reactions of toxic Microcystis aeruginosa PCC7806 and Daphnia magna. We hypothesize that a) the presence of D. magna will negatively affect growth, increase stress response and metabolites production in M. aeruginosa PCC7806 and b) the presence of M. aeruginosa PCC7806 will negatively affect physiological responses and life traits in D. magna. In order to test these hypotheses experiments were conducted in a specially designed co-culture chamber that allows exchange of the metabolites without direct contact. A clear mutual impact was evidenced. Cyanobacterial metabolites reduced survival of D. magna and decreased oxidative stress enzyme activity. Simultaneously, presence of D. magna did not affect photosynthetic activity. However, ROS increase and tendencies in cell density decrease were observed on the same day, suggesting possible energy allocation towards anti-oxidative stress enzymes, or other protection mechanisms against Daphnia infochemicals, as the strain managed to recover. Elevated concentration of intracellular and overall extracellular microcystin MC-LR, as well as intracellular concentrations of aerucyclamide A and D in the presence of Daphnia, indicating a potential protective or anti-grazing function. However, more research is needed to confirm these findings.

Regioselective, one-pot, multi-component, green synthesis of substituted benzo[c]pyrazolo[2,7]naphthyridines

An efficient and environmentally benign synthetic protocol has been developed for the synthesis of benzo[c]pyrazolo[2,7]naphthyridine derivatives through regioselective multi-component "on-water" reaction of isatin, malononitrile and 3-aminopyrazole. The Knoevenagel condensation of isatin with malononitrile resulted in the formation of arylidene, which subsequently underwent Michael addition with 3-aminopyrazole followed by basic hydrolysis, cyclization, decarboxylation and aromatization to give the target naphthyridines in good to excellent yields. The one-pot multi-component protocol was also employed to obtain the said naphthyridines in a lower yield (10-15%) than obtained by basic hydrolysis of spiro-intermediates. The present study shows attractive features such as the use of water as a green solvent, short reaction time, reduced waste products and transition metal free C-C and C-N bond formation. The structures of the synthesized derivatives were established through FTIR, 1H-NMR, 13C-NMR spectroscopy and ESI-mass spectrometry.

An algal process treatment combined with the Fenton reaction for high concentrations of amoxicillin and cefradine

The goal of the current study was to create a combined technique for the removal of two common antibiotics (amoxicillin and cefradine) using Fenton and an algal action process.

Pyrazole containing natural products: synthetic preview and biological significance

A large number of structurally diverse natural compounds containing azole nucleus constitute an important class of biologically active heterocycles that are gaining more attention in the field of medicinal chemistry. Among azoles, pyrazoles are rarely found in nature probably due to difficulty in the formation of N-N bond by living organisms. However, they exhibit numerous biological activities, including anti-diabetic, antiviral, anticancer, anti-inflammatory, antibacterial and antifungal activities. The present review is an attempt to understand the chemistry along with medicinal importance of pyrazole containing natural products reported till date which would certainly help the scientific community to bring further developments in the isolation and synthetic methodologies for pyrazole based novel bioactive compounds.

Generation of reactive oxygen species in cyanobacteria and green algae induced by allelochemicals of submerged macrophytes

Inhibition of phytoplankton by allelochemicals released by submerged macrophytes is reported to be one of the mechanisms that maintain a clear-water state in shallow lakes. In order to elucidate this mechanism, the ability of six polyphenols and two long-chain fatty acids to induce the generation of reactive oxygen species (ROS) in phytoplankton was studied using the ROS sensitive probe 2',7'- dichlorodihydrofluorescein diacetate (DCFH-DA). The results showed that only (+)-catechin (CA) and pyrogallic acid (PA) could induce ROS formation in Microcystis aeruginosa and Pseudokirchneriella subcapitata. 25 mg L⁻¹ CA caused 1.2, 1.4 and 1.8 times increase of ROS levels in M. aeruginosa at 1, 2 and 4h exposure, respectively, and, correspondingly in P. subcapitata cells, these values were 3.7, 6.2 and 7.7, respectively. PA also significantly increased the levels of intracellular ROS in P. subcapitata (P < 0.01); however, significant ROS generation in M. aeruginosa was observed at only 4h exposure (P < 0.01). Light enhanced ROS generation in CA treated cells, but not in the cells treated with PA. CA and PA may act as redox cyclers after uptake by test organisms and produce ROS successively. These results suggest that the oxidative stress induced by the redox cycling property of allelochemicals may be one of the important causes for the inhibitory effect of some submerged macrophytes towards undesired phytoplankton in natural aquatic ecosystems.