Bhavanath Jha

Isolation and characterization of extracellular polymeric substances from micro-algae Dunaliella salina under salt stress

Extracellular polymeric substances (EPSs), produced by Dunaliella salina strain, increase concomitantly with salt concentration and maximum (944 mg/l) were obtained at 5M NaCl, whereas minimum (56 mg/l) at 0.5M salinity. Emulsifying activity was measured in terms of strength to retain the emulsion and comparatively 85.76% retention was observed at 0.5M salinity thereafter it intends to decline. The FT-IR-spectra reveal characteristic functional groups NH stretching, asymmetrical CH stretching vibration of aliphatic CH(2)-group, CC stretching of aromatic, CN stretch of aliphatic amine, NH wag of primary amine and CX stretch of alkyl-halides with a stretching of COC, CO corresponding to the presence of carbohydrates. The FT-IR-spectra substantiated the presence of primary amine-group, aromatic-compound, halide-group, aliphatic alkyl-group and polysaccharides. Four monosaccharides (glucose, galactose, fructose and xylose) were also detected by HPLC analysis. Production of EPSs may allow further exploration of D. salina as potential EPSs producer and make it as a promising candidate for biotechnological and industrial exploitation.

Salt tolerance mechanisms in mangroves: a review

Mangroves are woody plants which form the dominant vegetation in tidal, saline wetlands along tropical and subtropical coasts. The current knowledge concerning the most striking feature of mangroves i.e., their unique ability to tolerate high salinity is summarized in the present review. In this review, we shall discuss recent studies that have focused on morphological, anatomical, physiological, biochemical, molecular and genetic attributes associated with the response to salinity, some of which presumably function to mediate salt tolerance in the mangroves. Here we shall also review the major advances recently made at both the genetic and the genomic levels in mangroves. Salinity tolerance in mangroves depends on a range of adaptations, including ion compartmentation, osmoregulation, selective transport and uptake of ions, maintenance of a balance between the supply of ions to the shoot, and capacity to accommodate the salt influx. The tolerance of mangroves to a high saline environment is also tightly linked to the regulation of gene expression. By integrating the information from mangroves and performing comparisons among species of mangroves and non-mangroves, we could give a general picture of salt tolerance mechanisms of mangroves, thus providing a new avenue for development of salt tolerance in crop plants through effective breeding strategies and genetic engineering techniques.

Selenium and spermine alleviate cadmium induced toxicity in the red seaweed Gracilaria dura by regulating antioxidants and DNA methylation.

The protective role of exogenously supplied selenium (Se) and polyamines (PAs) such as putrescine (Put) and spermine (Spm) in detoxifying the cadmium (Cd) induced toxicity was studied in the marine red alga Gracilaria dura in laboratory conditions. The Cd exposure (0.4 mM) impede the growth of alga while triggering the reactive oxygen species (ROS viz. O(2)(•-) and H(2)O(2)) generation, inhibition of antioxidant system, and enhancing the lipoxygenase (LOX) activity, malondialdehyde (MDA) level and demethylation of DNA. Additions of Se (50 μM) and/or Spm (1 mM) to the culture medium in contrast to Put, efficiently ameliorated the Cd toxicity by decreasing the accumulation of ROS and MDA contents, while restoring or enhancing the level of enzymatic and nonenzymatic antioxidants and their redox ratio, phycobiliproteins and phytochelatins, over the controls. The isoforms of antioxidant enzymes namely superoxide dismutase (Mn-SOD, ~150 kDa; Fe-SOD ~120 kDa), glutathione peroxidase (GSH-Px, ~120 and 140 kDa), glutathione reductase (GR, ~110 kDa) regulated differentially to Se and/or Spm supplementation. Furthermore, it has also resulted in enhanced levels of endogenous PAs (specially free and bound insoluble Put and Spm) and n-6 PUFAs (C20-3, n-6 and C20-4, n-6). This is for the first time wherein Se and Spm were found to regulate the stabilization of DNA methylation by reducing the events of cytosine demethylation in a mechanism to alleviate the Cd stress in marine alga. The present findings reveal that both Se and Spm play a crucial role in controlling the Cd induced oxidative stress in G. dura.

Bioengineering for Salinity Tolerance in Plants: State of the Art

Genetic engineering of plants for abiotic stress tolerance is a challenging task because of its multifarious nature. Comprehensive studies for developing abiotic stress tolerance are in progress, involving genes from different pathways including osmolyte synthesis, ion homeostasis, antioxidative pathways, and regulatory genes. In the last decade, several attempts have been made to substantiate the role of “single-function” gene(s) as well as transcription factor(s) for abiotic stress tolerance. Since, the abiotic stress tolerance is multigenic in nature, therefore, the recent trend is shifting towards genetic transformation of multiple genes or transcription factors. A large number of crop plants are being engineered by abiotic stress tolerant genes and have shown the stress tolerance mostly at laboratory level. This review presents a mechanistic view of different pathways and emphasizes the function of different genes in conferring salt tolerance by genetic engineering approach. It also highlights the details of successes achieved in developing salt tolerance in plants thus far.

Enzymatic hydrolysis and production of bioethanol from common macrophytic green alga Ulva fasciata Delile

The green seaweed Ulva which proliferates fast and occurs abundantly worldwide was used as a feedstock for production of ethanol following enzymatic hydrolysis. Among the different cellulases investigated for efficient saccharification, cellulase 22119 showed the highest conversion efficiency of biomass into reducing sugars than Viscozyme L, Cellulase 22086 and 22128. Pre-heat treatment of biomass in aqueous medium at 120°C for 1h followed by incubation in 2% (v/v) enzyme for 36 h at 45°C gave a maximum yield of sugar 206.82±14.96 mg/g. The fermentation of hydrolysate gave ethanol yield of 0.45 g/g reducing sugar accounting for 88.2% conversion efficiency. These values are substantially higher than those of reported so far for both agarophytes and carrageenophytes. It was also confirmed that enzyme can be used twice without compromising on the saccharification efficiency. The findings of this study reveal that Ulva can be a potential feedstock for bioethanol production.

Expression of SbGSTU (tau class glutathione S-transferase) gene isolated from Salicornia brachiata in tobacco for salt tolerance

Tau class glutathione transferases (GSTU) genes are plant specific, induced by different abiotic stress, and important for protecting plants against oxidative damage. GST gene was isolated using 5′ RACE from an extreme halophyte Salicorniabrachiata, cloned, sequenced and its protein structure was predicted. Transcript profiling of SbGST gene expression was studied under different abiotic stress conditions and plant growth regulator treatments, viz. salt, cold, drought, ABA and salicylic acid, with time period point and concentration point. The expression of SbGST gene was up-regulated in all stress conditions, except SA treatment. Seed germination percentage, GST enzyme assay, fresh weight and other growth parameters (root length, shoot length and leaf area) were studied and results indicate that over-expression of SbGST gene in transgenic tobacco leads to enhanced seed germination and growth under salt stress. Transgenic lines were evaluated for their performance under salt stress and tobacco plants over-expressing SbGST showed higher seed germination and survival compared to wild type. These results confirm that expression of SbGST gene is up-regulated by different stresses and over-expression of tau class SbGST gene in transgenic tobacco plays a vital role in abiotic stress tolerance. SbGST gene expressed conspicuously under salt stress leading to enhance seed germination and better growth. Furthermore, GST is a potential candidate gene to be used in genetic engineering for enhancing abiotic stress tolerance.

Fatty acid profiling of tropical marine macroalgae: An analysis from chemotaxonomic and nutritional perspectives

The lipid and fatty acid (FA) compositions for 100 marine macroalgae were determined and discussed from the context of chemotaxonomic and nutritional perspectives. In general, the lipid contents in macroalgae were low (2.3-20 mg/g fr. wt.) but with substantially high amounts of nutritionally important polyunsaturated fatty acids (PUFAs) such as LA, ALA, STA, AA, EPA and DHA, that ranged from 10% to 70% of TFAs. More than 90% of the species showed nutritionally beneficial n6/n3 ratio (0.1:1-3.6:1) (p≤0.001). A closer look at the FA data revealed characteristic chemotaxonomic features with C18 PUFAs (LA, ALA and STA) being higher in Chlorophyta, C20 PUFAs (AA and EPA) in Rhodophyta while Phaeophyta depicted evenly distribution of C18 and C20 PUFAs. The ability of macroalgae to produce long-chain PUFAs could be attributed to the coupling of chloroplastic FA desaturase enzyme system from a photosynthetic endosymbiont to the FA desaturase/elongase enzyme system of a non-photosynthetic eukaryotic protist host. Further, the principal component analysis segregated the three macroalgal groups with a marked distinction of different genera, families and orders, Hierarchical cluster analyses substantiated the phylogenetic relationships of all orders investigated except for those red algal taxa belonging to Gigartinales, Ceramiales, Halymeniales and Rhodymeniales for which increased sampling effort is required to infer a conclusion. Also, the groups deduced from FA compositions were congruent with the clades inferred from nuclear and plastid genome sequences. This study further indicates that FA signatures could be employed as a valid chemotaxonomic tool to differentiate macroalgae at higher taxonomic levels such as family and orders.

The roots of the halophyte Salicornia brachiata are a source of new halotolerant diazotrophic bacteria with plant growth-promoting potential

Soil salinity is the major cause limiting plant productivity worldwide. Nitrogen-fixing bacteria were enriched and characterised from roots of Salicornia brachiata, an extreme halophyte which has substantial economic value as a bioresource of diverse and valuable products. Nitrogen-free semisolid NFb medium with malate as carbon source and up to 4% NaCl were used for enrichment and isolation of diazotrophic bacteria. The isolates were tested for plant growth-promoting traits and 16S rRNA, nifH and acdS genes were analysed. For selected strains, plant growth-promoting activities were tested in axenically grown Salicornia seedlings at different NaCl concentrations (0–0.5M). New halotolerant diazotrophic bacteria were isolated from roots of S. brachiata. The isolates were identified as Brachybacterium saurashtrense sp. nov., Zhihengliuella sp., Brevibacterium casei, Haererehalobacter sp., Halomonas sp., Vibrio sp., Cronobacter sakazakii, Pseudomonas spp., Rhizobium radiobacter, and Mesorhizobium sp. Nitrogen fixation as well as plant growth-promoting traits such as indole acetic acid (IAA) production, phosphate solubilisation, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity were demonstrated. For Brachybacterium saurashtrense and Pseudomonas sp., significant plant growth-promoting activities were observed in Salicornia in salt stress conditions. Salicornia brachiata is a useful source of new halotolerant diazotrophic bacteria with plant growth-promoting potential.

Evidence for a plant-associated natural habitat for Cronobacter spp.

Cronobacter (Enterobacter sakazakii) species are responsible for rare cases of necrotising enterocolitis and bacteraemia in infants, as well as cases of meningitis with high case fatality rates in neonates and immunocompromised infants. Some physiological features, such as the production of a yellow pigment, the formation of a gum-like extracellular polysaccharide and the ability to persist in a desiccated state, suggest an environmental niche for these organisms. To date, the natural habitat of Cronobacter spp. remains unknown. In this report, the isolation and characterisation of two Cronobacter sakazakii strains from plant roots is described. Also, the root colonisation behaviour of Cronobacter strains originating from clinical and plant sources is assessed. The nine strains investigated showed features often found in plant-associated and rhizosphere microorganisms, including solubilisation of mineral phosphate and production of indole acetic acid. Siderophore production was observed for all except one strain. In addition, the capability to endophytically colonise tomato and maize roots was demonstrated for several strains, either by fluorescence in situ hybridisation, using fluorescently labelled oligonucleotide probes, or by using strains tagged with green fluorescent protein and confocal laser scanning microscopy. The results provide evidence that plants may be the natural habitat of Cronobacter spp.

Synthesis and characterization of agar-based silver nanoparticles and nanocomposite film with antibacterial applications

This study describes the synthesis and characterization of silver nanoparticles and nanocomposite material using agar extracted from the red alga Gracilaria dura. Characterization of silver nanoparticles was carried out based on UV-Vis spectroscopy (421 nm), transmission electron microscopy, EDX, SAED and XRD analysis. The thermal stability of agar/silver nanocomposite film determined by TGA and DSC analysis showed distinct patterns when compared with their raw material (agar and AgNO(3)). The TEM findings revealed that the silver nanoparticles synthesized were spherical in shape, 6 nm in size with uniform dispersal. The synthesized nanoparticles had the great bactericidal activity with reduction of 99.9% of bacteria over the control value. The time required for synthesis of silver nanoparticles was found to be temperature dependent and higher the temperature less the time for nanoparticles formation. DSC and XRD showed approximately the same crystalline index (CI(DSC) 0.73).