Rice-field Cyanobacterium Research Articles

Effects of temperature on morphology, physiology, and metabolic profile of diazotrophic cyanobacteria inhabiting diverse habitats

Global population expansion has increased the demand for food supply and agricultural productivity. Abiotic stressors like temperature have significantly restricted agriculture in cropland and jeopardized food security. Cyanobacteria play a crucial role in fostering sustainable agriculture and ensuring global food security. In the present study, we have assessed the effect of temperatures on diazotrophic free living rice-field and hot-spring cyanobacteria. They were treated to a variable range of temperatures to see the changes in cellular morphology, physiology, and biochemical characteristics. The rise of temperatures induces growth (60 %), total protein (54 %) contents of rice-field cyanobacterium until 25 °C, further treatment results in decline (20 %) at 45 °C. However, growth indices were increased till 35 °C (90 %) in hot-spring cyanobacterium and further treatment did not exhibit a significant decline in the same. However, the reactive oxygen species (ROS) generation and lipid peroxidation (LPO) were higher in rice-field (2.8 and 1.7 fold) as compared to hot-spring cyanobacterium (2.2 and 1.6 fold). In response to temperature, enzymatic antioxidant contents were much higher in hot-spring as compared to rice-field cyanobacterium. Similarly, carotenoid and carbohydrate content was also higher in hot spring (2 fold) as compared to rice-field cyanobacterium (1.5 and 1.2 fold). All these data collectively suggest that hot-spring (Nostoc sp. strain VKB02) has a higher thermoprotective capacity with novel defense mechanisms as compared to rice-field cyanobacterium (Anabaena sp. strain VKB01). These findings contributed to a better understanding of the temperature stress, improvement of agricultural productivity and future welfare of green ecosystems.

Synergistic effects of salt and ultraviolet radiation on the rice-field cyanobacterium Nostochopsis lobatus HKAR-21.

Environmental variation has a significant impact on how organisms, including cyanobacteria, respond physiologically and biochemically. Salinity and ultraviolet radiation (UVR)-induced variations in the photopigments of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21 and its photosynthetic performance was studied. We observed that excessive energy dissipation after UVR is mostly caused by Non-Photochemical Quenching (NPQ), whereas photochemical quenching is important for preventing photoinhibition. These findings suggest that ROS production may play an important role in the UVR-induced injury. To reduce ROS-induced oxidative stress, Nostochopsis lobatus HKAR-21 induces the effective antioxidant systems, which includes different antioxidant compounds like carotenoids and enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). The study indicates that Nostochopsis lobatus HKAR-21 exposed to photosynthetically active radiation + UV-A + UV-B (PAB) and PAB + NaCl (PABN) had significantly reduced photosynthetic efficiency. Furthermore, maximum ROS was detected in PAB exposed cyanobacterial cells. The induction of lipid peroxidation (LPO) has been investigated to evaluate the impactof UVR on the cyanobacterial membrane in addition to enzymatic defensive systems. The maximal LPO level was found in PABN treated cells. Based on the findings of this research, it was concluded that salinity and UVR had collegial effects on the major macromolecular components of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21.

UV-induced physiological changes and biochemical characterization of mycosporine-like amino acid in a rice-field cyanobacterium Fischerella sp. strain HKAR-13

Mycosporine-like amino acids (MAAs) are valuable secondary metabolite with notable photoprotective potential. The present study investigateS the imрасts of рhоtоsynthetiс асtive rаdiаtiоn (РАR) and ultraviolet radiation (UVR) on various physiological processes in the cyanobacterium Fischerella sp. strain HKAR-13. Cell viability was reduced by 36 and 65% after 72h of exроsure to РАR+UV-А (PA) and РАR+UV-А+UV-B (PAB) radiations respectively. Significant decline in Chl a content was observed during PA and PAB exposure after 36h. Carotenoid content increased significantly after 48h of exposure, thereafter began to decline. Cultures exposed to PAB showed maximum detrimental effect on protein synthesis. In PAB and PA, the levels of intracellular reactive oxygen species (ROS) increased significantly. Fluorescence microscopic images of cyanobacteria revealed generation of ROS in UVR as indicated by increase in green fluorescence. Besides, Fischerella sp. strain HKAR-13 was also tested for the рresenсe of MААs and their induction under UVR. UV-Vis spectrophotometry and high-рerfоrmаnсe liquid сhrоmаtоgrарhy аnаlyses revealed the рresenсe of a MAA having absorption maxima λmax 334 nm and retention time of 1.5 min. Maximum induction of MAA was found in samples exposed to PAB followed by PA. Based on electrospray ionization-mass sрeсtrоsсорy (m/z: 333+1), fourier transform infrared and nuclear magnetic resоnаnсe sрeсtrоsсорy, the MAA was identified as shinorine. Shinorine was found to be highly stable under some abiotic stress factors such as UV-B, temperature and H2O2. It also showed efficient antioxidant activity in a dose-dependent manner as depicted by in vitro antioxidant assays.

Exogenous application of phytohormones modulates pesticide-induced injury in two rice field cyanobacteria: Toxicity alleviation by up-regulation of ascorbate-glutathione cycle

Injudicious usage of insecticides poses a harmful impact on non-targeted biological nitrogen fixers i.e. cyanobacteria, thereby causing substantial loss to paddy productivity. Phytohormones are emerging novel tools to optimize the adverse effect of stress factors. The current study aimed to explore the impact of insecticide cypermethrin (Cyp1; 2 μg ml−1 and Cyp2; 4 μg ml−1) on growth, protein, and exopolysaccharides (EPS) contents, oxidative stress, and ascorbate- glutathione cycle in two paddy field cyanobacteria Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120; it also attempted to understand the regulatory role of two phytohormones: kinetin (KN, 20 nM) and indole acetic acid (IAA, 240 nM) on insecticide-induced toxicity. Insecticide at Cyp1 and Cyp2 doses diminished the growth by 10% and 30% in Anabaena sp. and by 7% and 23% in N. muscorum, respectively, and a similar reduction was documented in protein (excepts at Cyp1) and exopolysaccharides contents in both the cyanobacteria. Cypermethrin at tested doses caused cellular accumulation of oxidative biomarkers (SOR, H2O2, and MDA equivalents contents) in a concentration-dependent manner. At similar doses, the activity of AsA-GSH cycle enzymes ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR) was stimulated (except at Cyp2 dose) while the levels of metabolites ascorbate (AsA), glutathione (GSH), AsA+DHA (dehydroascorbate) and GSH+ GSSG (oxidized GSH) and the ratios of AsA/DHA and GSH/GSSG were declined. Exogenous application of KN and IAA alleviated the toxic impact of cypermethrin as evident by a reduction in cellular accumulation of oxidative biomarkers in both the cyanobacteria by further improving the activity of enzymes (APX, MDHAR, DHAR, and GR) and the levels of metabolites (AsA, GSH, AsA+DHA, GSH+GSSH, AsA/DHA, and GSH/GSSG) of AsA-GSH cycle. The current study suggests that enhanced efficiency of the AsA-GSH cycle regulates the level of H2O2 under limit due to exogenous application of both the phytohormones, directly favoring the growth of both the cyanobacteria and this effect of KN and IAA was more pronounced in N. muscorum suggesting its resistivity against stress.

Response of a rice-field cyanobacterium Anabaena sp. HKAR-7 upon exposure to ultraviolet-B radiation and ammonium chloride

Interactive effects of ultraviolet radiation (UVR), photosynthetically active radiation (PAR) and exogenously supplied ammonium chloride (NH4Cl) was studied in the rice-field cyanobacterium Anabaena sp. HKAR-7. The cyanobacterium was cultured under varying NH4Cl concentrations i.e., 0, 50, 200, 500, 1000 and 5000 μM and 200 μM (concentration) was found to be optimum for the growth of the cyanobacterium. Detrimental effects of UV-B exposure were observed on photosynthetic pigments such as chlorophyll a (Chl a), carotenoids and phycocyanin (PC). However, damage to these pigments was less in the cyanobacterial samples supplemented with NH4Cl. Contents of Chl a and PC in cyanobacterial cells decreased upon UV-B exposure but decrement was less in the samples supplemented with NH4Cl. Upon UV-B exposure, carotenoids content enhanced initially (till 15 days) during the course of treatment (21 days) but significant decrease (in carotenoids content) was observed in later phase of the experiment. From the results of photosynthetic activity, maximum quantum efficiency of PSII (Fv/Fm) and maximum electron transport rate (ETRmax), it could be concluded that exogenous supplementation of NH4Cl (optimum concentration) helped in protecting the cyanobacterial cells from highly energetic UVR to certain extent. Another interesting observation was significantly higher levels of biosynthesis and accumulation of mycosporine-like amino acids (MAAs) in the cyanobacterial cells supplemented with NH4Cl in comparison to non-supplemented cells. The purified MAA was identified to be phorphyra-334 as evidenced by UV/VIS absorption spectra, high performance liquid chromatography (HPLC) and electrospray ionization-mass spectrometry (ESI–MS).

Endophytic Colonization of Rice (Oryza sativa L.) by the Symbiotic Strain Nostoc punctiforme PCC 73102

Cyanobacteria are phototrophic microorganisms able to establish nitrogen-fixing symbiotic associations with representatives of all four of the major phylogenetic divisions of terrestrial plants. Despite increasing knowledge on the beneficial effects of cyanobacteria in rice fields, the information about the interaction between these microorganisms and rice at the molecular and structural levels is still limited. We have used the model nitrogen-fixing cyanobacterium Nostoc punctiforme to promote a long-term stable endophytic association with rice. Inoculation with this strain of hydroponic cultures of rice produces a fast adherence of the cyanobacterium to rice roots. At longer times, cyanobacterial growth in the proximity of the roots increased until reaching a plateau. This latter phase coincides with the intracellular colonization of the root epidermis and exodermis. Structural analysis of the roots revealed that the cyanobacterium use an apoplastic route to colonize the plant cells. Moreover, plant roots inoculated with N. punctiforme show both the presence of heterocysts and nitrogenase activity, resulting in the promotion of plant growth under nitrogen deficiency, thus providing benefits for the plant.

Dynamic population of N2-fixing cyanobacteria in an organic rice field

Abstract. Hendrayanti D, Rusmana I, Santosa DA, Hamim. 2019. Dynamic population of N2-fixing Cyanobacteria in an organic rice field. Biodiversitas 20: 2883-2890. The existence of free living N2-fixing cyanobacteria in rice fields has been acknowledged as an advantage for rice crops. At present, implementation of organic rice-systems has been increasing as an alternative way for keeping rice fields healthy. Therefore, investigation of N2-fixing cyanobacteria as a part of the soil components is important. Dynamic populations of the filamentous N2-fixing cyanobacteria assemblage in organic rice field at Ciparay, South Bandung, was investigated during the crop’s growth cycle (January-March 2018). Soil samples were collected from four plots of 20 ha rice fields. At each plot, soil from three random stations with three replications was taken using a 3-cm-diameter plastic cylinder. Composite samples from each station were analyzed for colony enumeration (TPC method), relative abundance and frequency, and species identification. The results show that population reached peak on the 80 days after planting (194 x 106 cfu/g soil). Species number decreased following increased density of the rice canopy. Among the 23 morphospecies found along the rice growth, four species were always found during all stages of growth: Halotia wernerae CSO2, Roholtiella mojavensis CSO6, Hapalosiphon welwitschii CSO7, and Desmonostoc danxiaense CSO3. The community of N2-fixing cyanobacteria found in the organic rice field was different to those reported from non-organic rice field.

Tolerance of wetland rice field's cyanobacteria to agrochemicals in cultural condition

Abstract The wetland rice fields are favorable for cyanobacterial growth, which play an important role in building soil fertility. Since agrochemicals are intensively being applied in rice fields to boost crop productivity, this study was undertaken to observe their effects on dominant N2-fixing cyanobacteria i.e. filamentous, heterocystous Nostoc linckia and unicellular Aphanothece pallida. These cyanobacteria were isolated from flooded rice fields and used to find out the effects of urea N-fertilizer, herbicide benthiocarb and insecticide metacid (in isolation and combinations) on their growth and N2-fixation ability. It was observed that N. linckia and A. pallida grew up to 25 days after inoculation (DAI) whereas acetylene reduction activity (ARA) increased up to 15 DAI in N-free medium without supplementation of agrochemicals in both cyanobacteria where N. linckia exhibited higher growth and ARA than A. pallida. Urea-N (30 ppm) was inhibitory for the growth of N. linckia whereas it stimulated the growth of A. pallida. Addition of benthiocarb (0.5 ppm) was found to have no significant impact on the growth of N. linckia but showed initial enhancement in the growth of A. pallida up to 10 DAI. Metacid supplementation at 0.25 ppm supported growth and ARA of both the cyanobacteria. It was also revealed that the use of urea-N, benthiocarb and metacid in combination reduced the growth and N2-fixation of N. linckia, however, these chemicals together were promotary for A. pallida. Overall, it was observed that combinations of these agrochemicals caused additive toxicity to heterocystous cyanobacterium whereas these were promotary to unicellular ones.

Thành phần loài vi khuẩn Lam (Cyanobacteria) trong đất trồng lúa ở một số xã thuộc huyện Nghĩa Đàn, tỉnh Nghệ An

THE SPECIES COMPOSITION OF CYANOBACTERIA IN RICE FIELDS OF NGHIA DAN DISTRICT, NGHE AN PROVINCE
 Nguyen Canh Hieu et al.
 Nghia Dan is a mountainous district of Nghe An province, stretching from 19013’ to 19033’ north latidute and between 105018’ to 105035’ east longitude. In August and December 2014 and in May 2015 we have investigated the species composition of Cyanobacteria distributing in rice fields of Nghia Dan district. We have found 40 species and subspecies in soil samples collected in 4 communes: Nghia Hung, Nghia My, Nghia Lam and Nghia Thuan. The most diverse genera were Oscillatoria (14 species and subspecies), Anabaena (6), Phormidium (5). There are 10 species and subspecies cyanobacteria contain heterocyst cells. Sorenxen coefficients between the sampling phases were from 0.82 to 0.88. Our study also showed that the numbers of species distributing at sampling sites were from 19 to 29 species.

An Efficient Method for the Separation and Purification of Phycobiliproteins from a Rice-Field Cyanobacterium Nostoc sp. Strain HKAR-11

The wide applications of phycobiliproteins (PBPs) are essentially dependent on the purity ratio for the production of quality products. In this study, we present a novel method for the separation and purification of PBPs subunits such as phycocyanin (PC) and phycoerythrin (PE) from a rice-field cyanobacterium Nostoc sp. strain HKAR-11 using gel filtration and single step hydrophobic interaction chromatography. The separation of PBPs subunits was done using cycles of gel filtration chromatography (Sephacryl-S100 HR) with the addition of 0.5 M NaCl in 50 mM phosphate buffer. The final purification of PE and PC was performed using a HiTrap Phenyl FF column and yielded a quite high purity ratio of 11.53 and 5.75 with 83 and 73 % remaining concentrations for PE and PC, respectively. The purity of PE and PC was confirmed by emission fluorescence with excitation at 563 and 615 nm, respectively. The native molecular weight of purified PE (44 kDa) and PC (34 kDa) was determined by gel filtration chromatography. The purified PE and PC were analyzed by SDS-PAGE that showed the presence of only two bands of α and β subunits in comparison to the bands of crude PBPs. To the best of our knowledge, this is the most efficient methodology for obtaining quite high purity index of PC and PE from any rice-field cyanobacterial source.

Cyanobacteria, pesticides and rice interaction

Cyanobacteria (blue-green algae) are widely distributed in tropical wet land rice fields where they play important role in building soil fertility. Due to their ability to photosynthesize and fixing atmospheric nitrogen, these are used as inoculants in rice fields to obtain additional benefits. The fertilizers and pesticides are being extensively used and therefore, it is necessary to find out effects of agrochemicals particularly pesticides on non target organisms like cyanobacteria. In the present investigation interaction of pesticides and cyanobacteria has been studied at different stages of rice crop. It was observed that application of herbicide butachlor decreased growth and N2-fixation of both native and inoculated cyanobacteria whereas insecticide metacid application was found to increase these attributes. The interaction of algal inoculation and both the biocides application were superior than algal inoculation with the herbicide application on both algae and rice. It is concluded from this study that herbicides application affected adversely cyanobacteria but insecticide application was favorable to them and application of both biocides was better than herbicide alone. Therefore judicious use of these chemicals and cyanobacteria in rice fields are suggested.

Biocidal spectrum of a rice field cyanobacterium <i>Nostoc</i> sp.

The antimicrobial efficacy of hexane, dichloromethane and ethyl acetate extracts of a rice-field cyanobacterium, Nostoc sp., were evaluated against cyanobacteria and phytopathogenic fungi. The maximum production of biocidal compounds was observed in cultures grown for 20 days under optimized conditions (phosphate =1.4 mg/l; light intensity ≈ 3000-4000 lux). Fractionation of the extracts showed six spots on silica-gel-coated plates. Hexane extract was the most potent biocide, showing marked (35-42%) reduction in the growth of fungi, but no negative influences on seed germination or seedling growth of wheat, rice and mung bean, emphasizing its suitability for use in agriculture.Keywords: Antifungal; extract; inhibition zone; metabolite; Pythium debaryanum; Rhizoctonia solani

Responses of a rice-field cyanobacterium Anabaena siamensis TISTR-8012 upon exposure to PAR and UV radiation

The effects of PAR and UV radiation and subsequent responses of certain antioxidant enzymatic and non-enzymatic defense systems were studied in a rice field cyanobacterium Anabaena siamensis TISTR 8012. UV radiation resulted in a decline in growth accompanied by a decrease in chlorophyll a and photosynthetic efficiency. Exposure of cells to UV radiation significantly affected the differentiation of vegetative cells into heterocysts or akinetes. UV-B radiation caused the fragmentation of the cyanobacterial filaments conceivably due to the observed oxidative stress. A significant increase of reactive oxygen species in vivo and DNA strand breaks were observed in UV-B exposed cells followed by those under UV-A and PAR radiation, respectively. The UV-induced oxidative damage was alleviated due to an induction of antioxidant enzymatic/non-enzymatic defense systems. In response to UV irradiation, the studied cyanobacterium exhibited a significant increase in antioxidative enzyme activities of superoxide dismutase, catalase and peroxidase. Moreover, the cyanobacterium also synthesized some UV-absorbing/screening substances. HPLC coupled with a PDA detector revealed the presence of three compounds with UV-absorption maxima at 326, 331 and 345nm. The induction of the biosynthesis of these UV-absorbing compounds was found under both PAR and UV radiation, thus suggesting their possible function as an active photoprotectant.

Developments in Cyanobacterial Biofertilizer

Rice is the world’s most important food crop as more than 40% of the world’s population depends on rice as a major source of calories. Rice yield in India is about 1990 kg/ha against a maximum of 3346 kg/ha in Punjab. Though the rice yields in Punjab is highest in the country, it is quite low compared to China (5807 kg/ha). Such diversity in yields is due to insufficient use of fertilizer nitrogen. Nitrogen is present as elemental nitrogen in the atmosphere and constitutes more than 79 per cent of total gases. However, crop plants cannot utilize nitrogen in elemental form. On global level, out of 180 million tonnes of nitrogen added annually on the earth’s surface, 2/3 is through biological processes, largely microbial activities. Cyanobacteria colonize rice fields and provide biologically fixed nitrogen to the rice crop to the extent of 25-30 kg nitrogen per hectare. In India, on an average, cyanobacteria accounts to about 33% of total algal flora of Indian rice field soils [66], whereas in some of the southern and eastern states this reaches up to 50%. Virtually all the dominant cyanobacteria in rice fields are nitrogen fixing. Apart from increase in yield and saving of fertilizer nitrogen, cyanobacterial inoculation improves the physico-chemical properties of soil, gradual build-up of residual soil nitrogen and carbon, improvement in soil pH and electrical conductivity. The grain quality in terms of protein content was improved. Our recent studies have shown that the cyanobacteria ( Nostoc and Anabaena ) were capable of forming associations with wheat roots grown in liquid culture. Probably, such cyanobacteria contribute nitrogen and growth promoting substances to plants in the rhizosphere.

Anilofos Tolerance and Its Mineralization by the Cyanobacterium Synechocystis sp. Strain PUPCCC 64

This study deals with anilofos tolerance and its mineralization by the common rice field cyanobacterium Synechocystis sp. strain PUPCCC 64. The organism tolerated anilofos up to 25 mg L−1. The herbicide caused inhibitory effects on photosynthetic pigments of the test organism in a dose-dependent manner. The organism exhibited 60, 89, 96, 85 and 79% decrease in chlorophyll a, carotenoids, phycocyanin, allophycocyanin and phycoerythrin, respectively, in 20 mg L−1 anilofos on day six. Activities of superoxide dismutase, catalase and peroxidase increased by 1.04 to 1.80 times over control cultures in presence of 20 mg L−1 anilofos. Glutathione content decreased by 26% while proline content was unaffected by 20 mg L−1 anilofos. The test organism showed intracellular uptake and metabolized the herbicide. Uptake of herbicide by test organism was fast during initial six hours followed by slow uptake until 120 hours. The organism exhibited maximum anilofos removal at 100 mg protein L−1, pH 8.0 and 30°C. Its growth in phosphate deficient basal medium in the presence of anilofos (2.5 mg L−1) indicated that herbicide was used by the strain PUPCCC 64 as a source of phosphate.

Induction of Sporulation By Different Nitrogen Sources InAnabaena naviculoides, A Diazotrophic Strain Capable of Colonizing Paddy Field Soil of Punjab (India)

Anabaena naviculoides is a filamentous cyanobacterium that is capable of heterotrophy and cellular differentiation into nitrogen-fixing heterocysts and desiccating thick walled spores, the akinetes. In the present study, the role of different nitrogen sources on akinete differentiation has been studied in the rice field cyanobacterium Anabaena naviculoides. All the vegetative cells transformrd into thick walled akinetes. In Chu-10 basal culture medium, the initiation of akinete differentiation was noticeable on 8th day and all the vegetative cells differentiated into akinetes by 50th day. Whereas among different nitrogen sources (ammonium sulphate, potassium nitrate, sodium nitrite, ammonium nitrate, Urea, ammonium chloride) employed, only potassium nitrate and sodium nitrite (2-10mM) enhanced the cyanobacterial growth and akinete development of the test organism. These two nitrogen sources shortened (32-36d) the period of akinete differentiation than the control cultures (50 d) and supported 100% (at 10mM) in a span of 32–36 days of culture. These akinetes (in dry state) remained viable for 105–150 days while vegetative cells under similar storage conditions (at 40°C) lost their viability after 15 days.

Toxicological impact of anilofos on some physiological processes of a rice field cyanobacterium Anabaena torulosa

This study deals with the toxicological impact of the herbicide anilofos on photosynthesis, respiration, nitrogen assimilation, and antioxidant system in a diazotrophic rice field cyanobacterium Anabaena torulosa. Treatment of anilofos (1.25, 2.5, and 5 mg L−1) affected growth, photosynthetic pigments, photosynthesis, and respiration of the cyanobacterium. Although all the photosynthetic pigments were affected, a maximum effect of the herbicide was observed on phycocyanin (51% reduction) followed by the carotenoids. The effect of the herbicide on photosynthetic pigments resulted in 57% decrease in photosynthetic O2 evolution. Studies on the photochemical activity demonstrated that both photosystems (PS I and PS II) were affected by the herbicide. Decrease in the photosynthesis rate resulted in decreased nitrogen assimilation, as revealed by reduced nitrate (20%) and ammonium (26%) uptake and decreased activities of nitrogenase (63% decrease) and glutamine synthetase (22% decrease). This ultimately resulted in the reduced growth of the organism. Activities of superoxide dismutase, catalase, and peroxidase in the presence of anilofos increased by 1.8–3.5 times over control cultures. Proline content increased by 1.6 times, while the content of ascorbate decreased slightly. These results indicate that the organism was able to tolerate the herbicide stress by activating oxidative stress defense mechanism.

Changes in fatty acid profile and antioxidant systems in a Nostoc muscorum strain exposed to the herbicide bentazon

A rational use of native cyanobacteria for diverse biotechnology purposes requires the study of the local abiotic factors that could potentially affect their normal growth. The present study deals with the herbicide bentazon (0.75, 1.5 and 2mM)-induced changes in lipid profile and antioxidative defense system parameters related to oxidative stress in the rice field cyanobacterium strain Nostoc muscorum UTAD_N213 grown under laboratory conditions for 72-h. Results indicate that the 72-h exposure of the strain to increasing bentazon concentrations caused: (1) a decrease of the polyunsaturated fatty acids (FAs); (2) an increase of the saturated FAs; and (3) a decrease of the unsaturation index. The activities of all of the antioxidant enzymes except for glutathione reductase showed a significant increase upon bentazon exposure in a time- and concentration-dependent manner. When compared to untreated controls, the oxidized glutathione content increased by 42, 79 and 119% with 0.75, 1.5 and 2mM bentazon, respectively, whereas the reduced to oxidized glutathione ratio decreased by 32, 50 and 61%, respectively. The accumulation of proline in cells after herbicide exposure might prevent bentazon-induced production of reactive oxygen species and functions as a protecting agent against oxidative damage.

Chlorpyrifos degradation by the cyanobacterium Synechocystis sp. strain PUPCCC 64

Indiscriminate use of insecticides leads to environmental problems and poses a great threat to beneficial microorganisms. The aim of the present work was to study chlorpyrifos degradation by a rice field cyanobacterium Synechocystis sp. strain PUPCCC 64 so that the organism is able to reduce insecticide pollution in situ. The unicellular cyanobacterium isolated and purified from a rice field was identified by partial 16S rRNA gene sequence as Synechocystis sp. strain PUPCCC 64. Tolerance limit of the organism was determined by studying its growth in graded concentrations (2.5-20 mg/L) of chlorpyrifos. Chlorpyrifos removal was studied by its depletion from the insecticide supplemented growth medium, and its biodegradation products were identified in the cell extract, biomass wash, and growth medium. The organism tolerated chlorpyrifos up to 15 mg/L. Major fraction of chlorpyrifos was removed by the organism during the first day followed by slow uptake. Biomass, pH, and temperature influenced the insecticide removal and the organism exhibited maximum chlorpyrifos removal at 100 mg protein/L biomass, pH 7.0, and 30°C. The cyanobacterium metabolized chlorpyrifos producing a number of degradation products as evidenced by GC-MS chromatogram. One of the degradation products was identified as 3,5,6-trichloro-2-pyridinol. Present study reports the biodegradation of chlorpyrifos by Synechocystis sp. Biodegradation of the insecticide by the cyanobacterium is significant as it can be biologically removed from the environment. The cyanobacterium may be used for bioremediation of chlorpyrifos-contaminated soils.

Bentazon triggers the promotion of oxidative damage in the Portuguese ricefield cyanobacterium Anabaena cylindrica: Response of the antioxidant system

Rice fields are frequently exposed to environmental contamination by herbicides and cyanobacteria, as primary producers of these aquatic ecosystems, are adversely affected. Anabaena cylindrica is a cyanobacterium with a significantly widespread occurrence in Portuguese rice fields. This strain was studied throughout 72 h in laboratory conditions for its stress responses to sublethal concentrations (0.75-2 mM) of bentazon, a selective postemergence herbicide recommended for integrated weed management in rice, with special reference to oxidative stress, role of proline and intracellular antioxidant enzymes in herbicide-induced free radicals detoxification. Activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione S-transferase (GST) increased in a time- and herbicide dose-response manner and were higher than those in the control samples after 72 h. A time- and concentration-dependent increase of malondialdehyde (MDA) levels and the enhanced cell membrane leakage following bentazon exposure are indicative of lipid peroxidation, free radicals formation, and oxidative damage, while increased amounts of SOD, CAT, APX, GST, and proline indicated their involvement in free radical scavenging mechanisms. The appreciable decline in the reduced glutathione (GSH) pool after 72 h at higher bentazon concentrations could be explained by the reduction of the NADPH-dependent glutathione reductase (GR) activity. The obtained results suggested that the alterations of antioxidant systems in A. cylindrica might be useful biomarkers of bentazon exposure. As the toxic mechanism of bentazon is a complex phenomenon, this study also adds relevant findings to explain the oxidative stress pathways of bentazon promoting oxidative stress in cyanobacteria.