Article

Effect of methylmercury on the carbohydrate production of Achnanthes longipes concomitant with sediment stabilization

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Achnanthes longipes cells were subjected to varying concentrations of methylmercury (6, 8, and 10 mM, and 6, 8and 10 µM) that were inoculated in the medium and allowed to incubate for seven days. Each set-up was prepared in three replicates and those without methylmercury added served as control. The amount of total carbohydrate produced from each setup was quantitated by phenol-sulfuric assay using spectrophotometric analysis. Varying absorbance values were observed in cultures treated with 6, 8, and 10 µM methylmercury but the differences were not statistically significant. Surprisingly, increasing the concentration of methylmercury even a thousand fold (6, 8, and 10mM) showed similar insignificantly varying results. To determine the effect on the stabilization of sediments, diatom cells were grown with sediment added as substrate. Overall, results indicated no significant difference between the control and the treatments. This implies that A.longipes is highly tolerant to methylmercury relative to the concentration used in the experiment. Mercury is one of the heavy metal toxicants in the aquatic environment which exists in the seawaters in its predominant organic complexes. This pollutant can have hazardous effects on the coastal environment including diatoms, which are important assemblage of algal community. Diatoms are a major component of marine and freshwater biofilms. Cells secrete extracellular polymeric substance composed of polysaccharides that vary in monosaccharide composition and serves a variety of functions; to include as main source of primary productivity, substratum adhesion, and its role in sediment stabilization. This research is conducted in an effort to understand the effect of methylmercury on the polysaccharide production by a benthic diatom Achnanthes longipes. Moreover, the consequent effect of the produced polysaccharide on sediment stabilization is also investigated as this may have important implications on coastal preservation and/or restoration. • Cells were grown in Erlenmeyer flasks with f/2 media at a salinity of ~30 psu in axenic condition. These were maintained in culture chamber at 18°C with an irradiance of 502.4 lux provided by fluorescent lamps. • Diatom cells were subjected to varying concentration of methylmercury (6, 8, and 10 µM and 6, 8 and 10 mM) that was inoculated in the medium and allowed to incubate for seven days. Each set-up was prepared in three replicates and the flasks without methylmercury added served as control. • The amount of total carbohydrate produced from each setup was quantitated by phenol-sulfuric assay at an absorbance of 485 nm using a spectrophotometer. A calibration curve was obtained with a regression value of 0.99 using glucose as standard. • To determine the effect on the stabilization of sediments, diatom cells were grown in the treatment conditions as previous but with sediment added as substrate. The sediment consisted of a mixture of sand (1%), silt (34%) and clay (65%), which were autoclaved to maintain the cultures in axenic condition. The cells were incubated for seven days. • Each culture was agitated using a mechanical stirrer at 160 rpm for 3 minutes. Sediment stability was measured according to the degree of re-suspension after agitation which was quantitated by spectrophotometric analysis. • Results showed highest carbohydrate concentration from the control (8.8µg/µL) with an average absorbance of 0.09AU. • Lower carbohydrate concentrations were obtained from the different treatments however, analysis of variance (ANOVA) showed that the difference was not statistically significant (p>0.05). Cultures treated with 6, 8, and 10 µM methylmercury showed carbohydrate concentrations of 6.5, 7.3, and 6.7 µg/µL, respectively with an average absorbance of ~0.07 AU. • Cultures treated with 6, 8, and 10 mM methylmercury produced 6.6, 6.9 and 6.7 µg/µL of carbohydrate, respectively with an average absorbance of ~0.07AU. Comparison between treatments was also analyzed using Tukey's test which showed no significant difference (p>0.05). Overall, results indicated no significant difference between the control and the treatments. • The absorbance values after re-suspension of the control and the sediments treated with 6, 8, and 10 µM, and 6, 8 and 10 mM did not vary significantly (p>0.05). Figure 1: Effect of methyl mercury on carbohydrate concentration and mean absorbance values of sediments with varying methyl mercury.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
The use of dredge material is a well-known technique for creating or restoring salt marshes that is expected to become more common along the Gulf of Mexico coast in the future. However, the effectiveness of this restoration method is still questioned. Wetland structural characteristics were compared between four created and three natural salt marshes in southwest Louisiana, USA. The created marshes, formed by the pumping of dredge material into formerly open water areas, represent a chronosequence, ranging in age from 3 to 19 years. Vegetation and soil structural factors were compared to determine whether the created marshes become more similar over time to the natural salt marshes. Vegetation surveys were conducted in 1997, 2000, and 2002 using the line-intercept technique. Site elevations were measured in 2000. Organic matter (OM) was measured in 1996 and 2002, while bulk density and soil particle-size distribution were determined in 2002 only. The natural marshes were dominated by Spartina alterniflora, as were the oldest created marshes; these marshes had the lowest mean site elevations (<30 cm NGVD). The six-year-old created marsh (formed in 1996) was higher in elevation (> 35 cm NGVD) and became dominated by high marsh (S. patens, Distichlis spicata) and shrub (Baccharis halimifolia, Iva frutescens) species. The higher elevation marsh seems to be following a different plant successional trajectory than the other marshes, indicating a relationship between marsh elevation and species composition. The soils in both the created and natural marshes contain high levels of clays (30–65 %), with sand comprising < 1 % of the soil distribution. OM was significantly greater and bulk density significantly lower in two of the natural marshes when compared to the created marshes. The oldest created marsh had significantly greater OM than the younger created marshes, but it may still take several decades before equivalency is reached with the natural marshes. Vegetation structural characteristics in the created marshes take only a few years to become similar to those in the natural marshes, just so long as the marshes are formed at a proper elevation. This agrees with other studies from North Carolina and Texas. However, it will take several decades for the soil characteristics to reach equivalency with the natural marshes, if they ever will.
Article
Cells of the marine diatom Asterionella glacialis treated with the organomercurial p-chloromercuribenzoate (PCMB) and cadmium, at growth retarding concentrations, exhibit decreased total fatty acid, polyunsaturated fatty acid and sterol contents. The level of individual fatty acids and sterols was also affected by metal treatment with significant decreases in the major polyunsaturated fatty acids 20:5Δ5,8,11,14,17, 16:1Δ9 and 16:3Δ3,6,9 in PCMB-treated, and 20:5Δ5,8,11,14,17 in cadmium-treated cells; increased cholest-5-en-3β-ol, particularly in PCMB-treated cells; and a decrease in the ratio of 24-ethylcholest-5-en-3β-ol to 24-ethylcholesta-5,24(28)Z-dien-3β-ol which was most notable in cadmium-treated cells. These results can be explained in terms of the formation of mercury and cadmium complexes with thiol-containing enzymes involved in lipid biosynthesis and metabolism, and thus provide further support for the hypothesis that transition metal toxicity is mediated by metal inactivation of physiologically essential, thiol-containing enzymes and co-factors.
Article
Synedra, a fresh water diatom, took up mercuric chloride rapidly from the surrounding water into the cells attaining the maximum level during the first 7 h. The comparison of mercury uptake by dividing cells with that of non-dividing, heat killed cells and their silicate shells showed that some factors other than cell-division or photosynthesis were responsible for mercury uptake by Synedra cells. About 20% of the total amount of mercury found in dividing cells was taken up by passive adsorption and could be eliminated by washing with distilled water or medium. About 50% of the mercury could not be eluted even with cysteine solution and was accumulated in the inner part of cells. Synedra took up 0·45 μm filterable or ionic mercury rather than particulate mercury larger than 0·45 μm.
Sediment stabilization utilizing the benthic diatom Achnanthes longipes (Bacillariophyceae)
  • M D Apoya-Horton
  • J Robinson
  • L Marcantel
  • B Shrestha
Apoya-Horton, M.D., Robinson, J., Marcantel, L. & Shrestha, B. Sediment stabilization utilizing the benthic diatom Achnanthes longipes (Bacillariophyceae). Poster presented at the 3 rd Annual Quality Day of McNeese State University, Lake Charles, Louisiana, USA. 29 April, 2009.