Lal Chand Rai

PHYCOLOGY AND HEAVY-METAL POLLUTION

1. All heavy metals, including those that are essential micronutrients (e.g. copper, zinc, etc.), are toxic to algae at high concentrations.

Ni (II) and Cr (VI) sorption kinetics by Microcystis in single and multimetallic system

The kinetics of Ni (II) and Cr (VI) sorption by Microcystis, was studied in single and multimetal systems. External mass transfer and intraparticle diffusion data suggested that Microcystis resembles a physical sorbent and therefore holds great potential for employment as a substitute (but requires revalidation at large scale) of physical sorbents in wastewater treatment. Microcystis showed better Ni (II) sorption efficiency than Cr (VI) in a single metal system at pH 6.4±0.1 and 6.0±0.3. However, in a multimetal system Ni (II) showed an insignificant difference from Cr (VI) due to a competitive effect. Sorption of Ni (II) and Cr (VI) was dependent on their initial concentration. The initial sorption rate showed non-proportionality with initial concentration (Co), and intraparticle diffusion rate parameters (Ki) which were not directly related to initial concentration (Ki=(Co)n where n=0.5). This suggests that neither external mass transfer rate nor intraparticle diffusion was a rate limiting factor. On fitting the experimental data both in first and second order equations, the regression analysis of second order equation gave a better r2 value. Thus, external mass transfer and intraparticle diffusion together are involved in the sorption process and pseudo second order equation provides an appropriate description than the first order equation.

Proteomics combines morphological, physiological and biochemical attributes to unravel the survival strategy of Anabaena sp. PCC7120 under arsenic stress

Proteomics in conjunction with morphological, physiological and biochemical variables has been employed for the first time to unravel survival strategies of the diazotrophic cyanobacterium Anabaena sp. PCC7120 under Arsenic (As) stress. Significant reduction in growth, carbon fixation, nitrogenase activity and chlorophyll content after 1 day (1d) and recovery after 15 days (15d) of As exposure indicates the acclimation of the test organism against As stress. The formation of akinete like structures is a novel observation never reported before in Anabaena sp. PCC7120. Proteomic characterization using 2-DE showed average 537, 422 and 439 spots in control, 1 and 15d treatment respectively. MALDI-TOF and LC-MS of As-treated Anabaena revealed a total of 45 differentially expressed proteins, of which 13 were novel (hypothetical) ones. Down-regulation of phosphoglycerate kinase (PGK), fructose bisphosphate aldolase II (FBA II), fructose 1,6 bisphosphatase (FBPase), transketolase (TK), and ATP synthase on day 1 and their significant recovery on the 15th day presumably maintained the glycolysis, pentose phosphate pathway (PPP) and turnover rate of Calvin cycle, hence survival of the test organism. Up-regulation of catalase (CAT), peroxiredoxin (Prx), thioredoxin (Trx) and oxidoreductase appears to protect the cells from oxidative stress. Appreciable induction in phytochelatin content (2.4 fold), GST activity (2.3 fold), and transcripts of phytochelatin synthase (5.0 fold), arsenate reductase (8.5 fold) and arsenite efflux genes - asr1102 (5.0 fold), alr1097 (4.7 fold) reiterates their role in As sequestration and shielding of the organism from As toxicity. While up-regulated metabolic and antioxidative defense proteins, phytochelatin and GST work synchronously, the ars genes play a central role in detoxification and survival of Anabaena under As stress. The proposed hypothetical model explains the interaction of metabolic proteins associated with the survival of Anabaena sp. PCC7120 under As stress.

Physiological and Biochemical Characteristics of a Copper Tolerant and a Wild Type Strain of Anabaena doliolum Under Copper Stress

Summary Copper tolerance in Anabaena doliolum has been studied by comparing the physiological properties of its wild type and Cu-tolerant strains. A concentration dependent reduction in growth, pigments, protein, sugar, lipid and ATP content, photosynthetic electron transport chain, O2-evolution, carbon fixation, nutrient uptake (NH+4 and NO--3), nitrate reductase, nitrogenase, glutamine synthetase and alkaline phosphatase activities was noticed in both the strains following Cu-supplementation. The reduction in all parameters was higher in wild type than the tolerant strain. The latter produced a larger (19.5 %) lipid fraction than the wild type even in the absence of added metal. As compared to the wild strain, the tolerant strain showed enhanced enzyme activities, especially of alkaline phosphatase (20 % higher), low copper uptake and insignificant loss of K+ and Na+. The data on lipid production, loss of K+ and Na+, and uptake of copper collectively indicate a change in the permeability of the plasma membrane and a possible operation of «exclusion mechanism» in the tolerant strain thereby reducing the toxic effect of copper even at a high concentration.

Influence of culture density, pH, organic acids and divalent cations on the removal of nutrients and metals by immobilized Anabaena doliolum and Chlorella vulgaris

The potential of alginate-immobilized Anabaena doliolum and Chlorella vulgaris was assessed for removal of nutrients (NOinf3sup-and NHinf4sup+) and metals (Cr2Oinf7sup2-and Ni2+) at different biomass concentrations (0.05, 0.1, 0.25, 0.49 and 1.22 g dry wt l-1) and pH values (4 to 10). Though uptake of all these substances was higher in concentrated algal beads (0.25, 0.49 and 1.22 g dry wt l-1), their rate of uptake was significantly (P<0.001) lower than that of low (0.05 g dry wt l-1) cell density beads. For A. doliolum, there was no significant difference in uptake rates for beads having densities of 0.05 and 0.1 g dry wt l-1. Chlorella vulgaris, however, showed maximum efficiency at 0.1 g dry wt l-1. Uptake of both the nutrients and the metals was maximal at pH 7 followed by pH 8, 6, 9, 10, 5 and 4. Of the different substances (organic acids and divalent cations) used, humic acid was most efficient in decreasing metal uptake. Mg2+ was, however, more efficient than Ca2+ in decreasing Ni2+ uptake. Immobilized algae with a cell density of 0.1 g dry wt l-1 were the most efficient for nutrient and metal removal at pH 6 to 8.

Interactive effects of UV-B and heavy metals (Cu and Pb) on nitrogen and phosphorus metabolism of a N2-fixing cyanobacterium Anabaena doliolum

Abstract This study demonstrated a general decrease in uptake of NH4+, urea and PO43−, activities of nitrogenase, glutamine synthetase, urease, alkaline phosphatase and ATPase following ultraviolet-B (UV-B) treatment and metal exposure, separately. As compared with an individual stressor the effect of their combination was more detrimental to the above processes. In contrast, a significant increase in NO3− uptake and nitrate reductase activity, following exposure of Anabaena doliolum to UV-B was observed. Kinetic study of all the processes demonstrated that the UV-B-induced structural change(s) in the enzymes/carriers could be responsible for uptake and assimilation of these nutrients. However, the metals seem to compete for the binding sites of the above enzymes/carriers. A synergistic interaction of UV-B and metals (Cu/Pb) seems to be due to an increased metal uptake by an altered membrane permeability, as a result of peroxidation of membrane lipids in UV-B exposed cells.

Protective effects of certain environmental factors on the toxicity of zinc, mercury, and methylmercury to Chlorella vulgaris

The specific growth rate and final yield of Chlorella vulgaris treated with zinc, mercury, and methylmercury declined with increase in metal concentration. Methylmercury was most toxic and at 1 × 10−3 mg/liter concentration it reduced survival by about 50%. Approximately 50% mortality occurred at 25 and 0.4 mg/liter concentration of zinc and mercury, respectively. The total chlorophyll content decreased and the carotenoids/chlorophyll ratio increased with increase in heavy metal concentration. Of the various factors investigated, pH, phosphate, and calcium produced a highly significant (P < 0.001) effect on metal toxicities, and magnesium produced a less significant effect (P < 0.1). The present study suggests that alkaline and hard eutrophic waters might help protect freshwater organisms against heavy metal toxicity.

Heavy Metal Tolerance in Algae

Algae are often exposed to heavy metal pollution due to the disposal of industrial and domestic wastes into waterways. Many algae growing in metal–polluted environments display an ability to tolerate high concentrations of toxic metals (De Filippis and Pallaghy 1994). In fact, even laboratory cultures of some algae can be acclimated to elevated concentrations of toxic metals (Shehata and Whitton 1982; Kuwabara and Leland 1986; Rai et al. 1991; Twiss et al. 1993). Metal tolerance in algae may be genetic or physiological, and the available reports often do not distinguish between these two different sets of mechanisms. The phrases tolerance and resistance have often been used interchangeably, although the latter phrase may be preferred if ability to withstand high concentrations of metals is genetically fixed.

Interactive effects of UV-B and copper on photosynthetic activity of the cyanobacterium Anabaena doliolum

Abstract This study presents information on the inhibition of carbon fixation, O2-evolution, photosynthetic electron transport chain, ATP pool and respiration rate of the cyanobacterium A. doliolum by UV-B and Cu. Interaction of UV-B (12.9 mWm−2 nm−1 for 12 and 25 min) and Cu2+ (0.3 and 0.5 μg ml−1) significantly increased the respiration rate and caused a shift from O2-evolution to O2-consumption. PSII exhibited the highest sensitivity to UV-B and Cu. A failure to restore DCPIP photoreduction by artificial electron donors (DPC, NH2OH and MnCl2) suggested that UV-B primarily inhibits the PSII reaction centre. Cu, however, reacts at multiple sites of the electron transport chain. The reduction and blue shifting of absorption peaks, suppression of fluorescence intensity and the excitation spectra indicate the involvement of phycobiliproteins in the inhibition of PSII activity. The synergistic interaction of UV-B and Cu appears due to increased Cu uptake brought about by an altered membrane permeability as a result of peroxidation of membrane lipids in the UV-B exposed cells.

Comparative proteomics unveils cross species variations in Anabaena under salt stress

UNLABELLED The present study compares protein diversity within three Anabaena species (Anabaena doliolum, Anabaena sp.PCC 7120 and Anabaena L31). 2-DE based analysis of 256 protein spots in control and 1, 3, 5, and 7days of salt treatment resulted into 96 proteins arching across fourteen functional categories were assigned to biochemical pathways using KOBAS 2.0. While 52.34% of the evaluated protein spots were common across three species, the remaining 47.66% fraction mainly comprised of the hypothetical and unknown proteins. PSORTb, CDD, Motifscan and Pfam revealed function and subcellular localization for 27 of the 31 hypothetical and unknown proteins. The differences in high salt tolerance (LC50) of A. doliolum over A. L31 was reflected by (i) many fold accumulation (as spot volumes) of Alr3090, Alr0803, peptidyl prolyl cis-trans isomerase and modulator of DNA gyrase proteins, and (ii) a better photosynthesis and energy homeostasis as indicated through photosystem activity, respiration, ATP and NADPH contents. Some common noteworthy salt effects include (i) photosystem damage, (ii) DNA damage repair, (iii) upregulated protein synthesis, (iv) enhanced sulphur metabolism, and (v) upregulated pentose phosphate pathway. 34 of the identified protein spots are novel entries to the Anabaena salt proteome. This study reveals the existence of separate strategies even within species to combat stress. BIOLOGICAL SIGNIFICANCE This study for the first time enumerates protein diversity in three Anabaena species employing their presence/absence and relative abundance. Proteomics integrated with physiology and bioinformatics deciphers differential salt tolerance among the studied species and is the first of its kind to predict the function of hypothetical and unknown proteins. Salt-induced proteomic alterations clearly demonstrate significant metabolic shifts and existence of separate molecular phenome among the species investigated. This may be responsible for niche specificity limiting their application as biofertilizer. Of the 96 identified proteins, a large chunk are new entries to the Anabaena salt proteome while some protein genes may be used as potential candidates for engineering salt tolerant cyanobacteria.