Sunil Pabbi

Cyanobacteria: A Potential Biofertilizer for Rice

Application of high input technologies has resulted in significant increase in agricultural productivity. There is, however, a growing concern about the adverse effects of indiscriminate use of chemical fertilizers on soil productivity and environmental quality. Cyanobacteria offer an economically attractive and ecologically sound alternative to chemical fertilizers for realizing the ultimate goal of increased productivity, especially in rice cultivation. In a wetland rice ecosystem, nitrogen fixation by free living cyanobacteria also significantly supplements soil nitrogen.

Effects of paraquat on lipid peroxidation and antioxidant enzymes in aquatic fern Azolla microphylla

Paraquat is most extensively used methyl viologen herbicide to control weeds in the rice-Azolla ecosystem. The effects of different paraquat (PQ) dosages on growth, lipid peroxidation, and activity of antioxidant enzymes of Azolla microphylla Kaul. were investigated. The results indicated that Azolla fronds survived only at the concentrations of 2–6 μM PQ. Frond fragmentation and browning occurred after 24 h at 8 μM PQ. At 24 h, the amount of proteins decreased by 48.7 % in Azolla fronds exposed to 10 μM PQ than that in control fronds. The supplementation of 10 μM PQ increased the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) by 2,4-, 1,8-, 3,0-, and 2,2-fold, respectively, as compared with control. The content of PQ and activities of SOD, CAT, GPX, and APX were found to be positively correlated. Our study showed that PQ (2–6 μM) caused ROS overproduction in Azolla fronds, which were scavenged by induced activities of antioxidant enzymes.

Studies on mineral phosphate solubilization by cyanobacteria Westiellopsis and Anabaena

Two diazotrophic cyanobacteria, Westiellopsis prolifica and Anabaena variabilis were evaluated for elucidating the possible mechanism of mineral phosphate solubilization. Phosphate starved cyanobacteria evaluated for the presence of organic acids, extracellular compounds or enzymes that might have been produced and promoted the mineral phosphate solubilization with Mussorie Rock Phosphate and Tricalcium Phosphate as substrates. Both the cultures did not reveal production of organic acids throughout the incubation period when checked for decrease in media pH of the media and thin layer chromatography. Thin layer chromatography of culture filtrates showed the presence of hydrocarbon like compound. Further analysis of the culture filtrates with gas liquid chromatography, a single peak near to the retention time of 7.6 was observed in all extracts of culture filtrates irrespective of phosphate source. UV-visible spectra of culture filtrates revealed the absorption maxima of 276 nm. Gas chromatographic-mass spectrometric analysis of culture filtrates showed most intense peak in the electron impact (EI) ionization was at m/z 149 and molecular ion peaks at m/z 207 and 167, inferring the presence of phthalic acid. Among the mechanisms in mineral phosphate solubilization, it was evident that these cyanobacteria used phthalic acid as possible mode of P solubilization.

Morphological characterization and molecular fingerprinting of Nostoc strains by multiplex RAPD

Morphological parameters studied for the twenty selected Nostoc strains were mostly found to be consistent with the earlier reports. But the shape of akinetes observed in this study was a little deviation from the existing descriptions and heterocyst frequency was also found to be different in different strains in spite of growing in the same nitrogen free media. Multiplex RAPD produced reproducible and completely polymorphic amplification profiles for all the strains including some strain specific unique bands which are intended to be useful for identification of those strains. At least one to a maximum of two unique bands was produced by different dual primer combinations. For ten strains out of twenty, strain specific bands were found to be generated. Cluster analysis revealed a vast heterogeneity among these Nostoc strains and no specific clustering based on geographical origin was found except a few strains. It was also observed that morphological data may not necessarily correspond to the genetic data in most of the cases. CCC92 (Nostoc muscorum) and CCC48 (Nostoc punctiforme) showed a high degree of similarity which was well supported by high bootstrap value. The level of similarity of the strains ranged from 0.15 to 0.94. Cluster analysis based on multiplex RAPD showed a good fit revealing the discriminatory power of this technique.

Characterization of 2,3-butanediol-forming and valine-sensitive α-acetolactate synthase of Enterobacter cloacae

Abstractα-Acetolactate synthase (α-ALS) of Enterobacter cloacae ATCC 27613 was purified to homogeneity by ammonium sulphate precipitation, Sephadex G-200 gel filtration and hydroxyapatite affinity chromatography. The molecular weight of the enzyme was found to be 60 kDa by SDS–polyacrylamide gel electrophoresis and ∼200 kDa by gel filtration through Sephadex G-200, showing that the enzyme is a homotrimer. The Km and Vmax of the enzyme were 20 mM and 200 μmol min−1 mg (protein)−1 respectively. The enzyme was optimally active at pH 6.0–8.0, 37 °C and showed concentration-dependent sensitivity to cofactors viz. FAD, NADP and NADPH and branched chain amino acids: leucine, isoleucine and valine. Substances like sodium formate, sodium acetate and sodium propionate, sugars and the selected intermediates of glycolytic pathway inhibited the enzyme. Glycerol, BSA and pyruvate-TPP stabilized the α-ALS. The enzyme showed the properties of both a catabolic as well as an anabolic α-ALS.

Cyanobacterial pigments: Perspectives and biotechnological approaches

Cyanobacteria are the oxygenic photosynthesis performing prokaryotes and show a connecting link between plastids of eukaryotic autotrophs and prokaryotes. A variety of pigments, like chlorophyll, carotenoids and phycobiliproteins which exhibit different colors are present in cyanobacteria. Increasing consciousness about the harmful effects of synthetic or chemical dyes encouraged people to give more preference towards the usage of natural products, such as plant or microbial-derived colors in food and cosmetics. That is why cyanobacteria are exploited as a source of natural colors and have high commercial value in many industries. This review mainly focuses on different cyanobacterial pigments, their applications and modern biotechnological approaches such as genetic engineering, systems biology to enhance the production of biopigments for their potential use in pharmaceuticals, food, research, and cosmetics industries.

A comparative study reveals the higher resolution of RAPD over ARDRA for analyzing diversity of Nostoc strains

Nostoc is a diverse genus of filamentous cyanobacteria with tremendous potential for agricultural and industrial applications. Morphometric methods and routine 16S rDNA-based identification undermines the genetic diversity and impedes strain-level differentiation. A comparative study to deduce the discriminatory power of random amplified polymorphic DNA (RAPD) and amplified ribosomal DNA restriction analysis (ARDRA) for analyzing the genetic diversity of 20 Nostoc strains of diverse geographical origin was carried out. The RAPD primer used in the study generated 100% polymorphic profile. HIP TG primer produced the highest number of bands and fragments. Five primers, viz. OPA 08, OPA 11, HIP GC, OPAH 02 and OPF 05 could produce unique bands for 11 strains. Cluster analysis using the RAPD profile showed 12.5–25% similarity among the strains. Following in silico restriction analysis, two restriction enzymes, viz. HaeIII and HinfI were selected for ARDRA. However, clustering based on the restriction pattern showed 22.5–100% similarity. Results of the present study clearly indicate higher resolution of RAPD which can be reliably used for strain-level differentiation of Nostoc strains.

Cyanobacterial Phycobilins: Production, Purification, and Regulation

The cyanobacteria are a diverse group of prokaryotic organisms that carry out oxygenic photosynthesis and are thought to be responsible for the oxygenation of our atmosphere. Like red algae and cryptomonads, cyanobacteria also contain phycobiliproteins (PBPs) which serve as major accessory pigments during photosynthesis. PBPs are large water-soluble supramolecular protein aggregates involved in light harvesting and can be divided broadly into three classes, viz., phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (APC) based on their spectral properties. PBPs have been extracted and purified from Spirulina spp., Synechococcus sp., Oscillatoria sp., etc., and produced commercially from Spirulina platensis, Anabaena sp., and Galdieria sulphuraria. Since cyanobacteria exhibit wide variations in nutrient availability, light intensity, light quality (wavelength), temperature, water activity, etc., these variations also result in altered metabolic activity of these organisms as a result of differential expression of different genes. The expression of phycobiliprotein coding genes is also accordingly modulated to adapt to a particular condition. Many workers have reported changes in phycobilisome structure and expression of cpc genes in response to light quality, light quantity, and nutrients like nitrogen, sulfur, etc. The composition and function of phycobiliproteins in cyanobacteria have also been reported to change under stress conditions. In the present paper, we have reviewed the production, purification, and regulation of cyanobacterial phycobilins including their importance in the commercial sector, as they have several applications as natural dyes in food and cosmetic industry, immunological assays, health-promoting properties, and broad range of other pharmaceutical applications.

Blue Green Algae: A Potential Biofertilizer for Rice

The biofertilizers, which are low cost inputs, renewable and pollution free have a crucial role in augmenting nutrient supply to crops by increasing their availability through exploitation of natural processes like biological nitrogen fixation, solubilization of insoluble P and decomposition of organic wastes etc. Blue Green Algae (BGA) find a highly favourable abode in the waterlogged conditions of rice fields and provide cheap nitrogen to plants besides increasing crop yield by making soil vital, fertile and productive. BGA biofertilizer in rice popularly known as “Algalization” helps in creating an environmentally safe agro ecosystem that ensures economic viability in paddy cultivation while saving energy intensive inputs. The agricultural importance of these organisms lies in their capacity to metabolize the molecular nitrogen, liberation of part of fixed nitrogen and growth promoting substances as extra metabolites, solubilising the insoluble phosphates, addition of organic matter and improving the physical and chemical nature of soil. Based on the natural ecology of these organisms, a rural oriented algal biofertilizer technology was developed which could be easily adopted by farmer for multiplication at their own level. The technology was introduced as a package of practices in a number of Indian states and showed positive results in terms of saving on chemical nitrogenous fertilizers and increasing crop yield. The technology has been substantially improved and the basic changes include; indoor production of algal biomass under semi-controlled conditions in a polyhouse for round the year production, a suitable and cheap growth medium for faster growth of the organisms and mixing with a suitable carrier material in desired quantities that supports higher microbial load with longer shelf life. This has also considerably reduced the quantity of inoculum per unit area. The product has been extensively tested in the field and established the advantage of using cyanobacterial inoculation in rice crop and its adoption as a management practice. It leads not only to saving on expensive inorganic chemical fertilizer but also sustains productivity by maintaining a continuous supply of crop nutrients. Considering the immense market potential, it is now desired that these products be exploited commercially.

Differential responses of hydrogen peroxide, lipid peroxidation and antioxidant enzymes in Azolla microphylla exposed to paraquat and nitric oxide

The present investigation was carried out to decipher the interplay between paraquat (PQ) and exogenously applied nitric oxide (NO) in Azolla microphylla. The addition of PQ (8 μM) increased the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) by 1.7, 2.7, 3.9 and 1.9 folds respectively than that control in the fronds of Azolla. The amount of H2O2 was also enhanced by 2.7 times in the PQ treated plants than that of control. The supplementation of sodium nitroprusside (SNP) from 8–100 μM along with PQ, suppressed the activities of antioxidative enzymes and the amount of H2O2 compared to PQ alone. The drop in the activity of antioxidative enzymes — SOD, GPX, CAT and APX was highest (39.9%, 48.4%, 41.6% and 41.3% respectively) on the supplementation of 100 μM SNP with PQ treated fronds compared to PQ alone. The addition of NO scavengers along with NO donor in PQ treated fronds neutralized the effect of exogenously supplied NO. This indicates that NO can effectively protect Azolla against PQ toxicity by quenching reactive oxygen species. However, 200 μM of SNP reversed the protective effect of lower concentration of NO donor against herbicide toxicity. Our study clearly suggests that (i) SNP released NO can work both as cytoprotective and cytotoxic in concentration dependent manner and (ii) involvement of NO in protecting Azolla against PQ toxicity.