Browsing by Author "Rathnayake, I. V. N."

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Biosurfactant production by bacteria isolated from petroleum contaminated soil
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Sandeepani, A. M. S.; Rathnayake, I. V. N.
Biosurfactants are surface-active biomolecules produced by microorganisms, which are useful biomolecules in the remediation of petroleum contaminated environments. Two bacterial strains isolated from petroleum-contaminated soil of selected motor vehicle workshops and filling stations were screened and characterized morphologically and biochemically. The biosurfactantproducing ability of the strains was determined qualitatively and quantitatively by enrichment culture, hemolytic activity assay, Cetyltrimethylammonium bromide (CTAB) assay, oil displacement assay, foaming activity, and emulsification activity measurement. After conducting various morphological and biochemical studies, the strains were identified as bacteria belonging to the genus Pseudomonas and the genus Micrococcus. Both bacteria gave positive results for hemolytic activity, CTAB assay, and foaming activity, which gives beta-hemolysis on blood agar, blue colour halos, and stable foam, respectively. The highest displacement was observed from Pseudomonas where the diameter was 6.0 cm, while Micrococcus showed 3.6 cm activity. Although both bacteria showed an emulsion after 1 minute, the Pseudomonas strain showed the highest maximum emulsification index (E24%) of 57.1%. This suggests that the Pseudomonas strain could have more potential to facilitate the remediation of hydrocarbon-contaminated sites and produce a higher yield of biosurfactants than the Micrococcus strain.
Characterization of lipolytic bacteria isolated from oil mill waste
(Faculty of Humanities, University of Kelaniya, 2023) Dias, P. P. C. M.; Rathnayake, I. V. N.
Microbial lipases are enzymes that can catalyze the hydrolysis of esters formed from glycerol and long-chain fatty acids. Microbial lipases are used as biocatalysts in various biotechnological applications due to their stability in organic solvents. In the present study, a bacterial culture isolated from oil mill waste was characterized using morphological, cultural, and biochemical properties. Isolate was subjected to qualitative screening of extracellular lipolytic activity using culture-based methods on Tween peptone agar, olive oil with phenol red agar, and egg yolk agar. The lipase was produced using submerged fermentation. Fermented culture supernatant was used as the crude lipase. The crude lipase was extracted, and the activity was measured using olive oil as the substrate, and the concentration of the free fatty acid in the reaction was determined by titrating with 0.1 M NaOH. The effect of detergent on crude lipase activity was also assessed using three different commercial detergents. Based on morphological, cultural, and biochemical characteristics, the strain was identified as a bacterium belonging to the genus Pseudomonas. This bacterium showed the opaque zone on tween peptone agar and egg yolk agar and it displayed a yellow zone on phenol red agar. Crude lipase of this bacterium showed 14.50 μmol/h/mL of activity at 37 ̊ C and pH 8. Crude lipase investigated in the study showed varying relative activities to the three detergents tested, 51.8% being the highest. The lipolytic capabilities of the isolated bacterial strain hold great promise for various biotechnological applications requiring the enzymatic breakdown of lipids.
Comparison of the tolerance of cadmium (Cd2+), lead (Pb2+) and their mixtures by Staphylococcus sp. isolated from a water body receiving textile effluent
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Aththanayake, A. M. K. C. B.; Rathnayake, I. V. N.; Deeyamulla, M. P.
Cd2+ and Pb2+ are widely used heavy metals in industries such as electroplating, battery, plastic and pigment production etc. These heavy metals are considered as highly threatening substances to human body, which can cause carcinogenic effects and organ dysfunctions. The isolated Staphylococcus sp. from waste effluent was exposed to a range of single and mixed metal concentrations of Cd2+ and Pb2+ in modified Tris-minimal medium. The growth patterns of Staphylococcus sp. during 24-hour intervals were monitored spectrophotometrically at 600 nm. The effective concentrations (EC50) of Staphylococcus sp. were calculated up to 72 hours. Staphylococcus sp. showed a gradually increasing growth in Pb2+ containing medium, where as a decreasing growth in Cd2+ containing medium was observed after 48 hours. It showed an increasing growth when grown in the presence of both metals. EC50 values at 24, 48 and 72 hours with Cd2+ and their mixture showed a gradual decrease while EC50 values of Pb2+ showed a gradual increase. Results of the study indicated that Staphylococcus sp. has comparatively high tolerance to Pb2+ than Cd2+ and their mixtures
Potential use of Chlorella vulgaris KCBAL01 from a freshwater stream receiving treated textile effluent in hexavalent chromium [Cr(VI)] removal in extremely acidic conditions
(Journal of Environmental Science and Health, 2022) Aththanayake, A. M. K. C. B.; Rathnayake, I. V. N.; Deeyamullab, M. P.; Megharaj, Mallavarapu
Remediation of hexavalent chromium with conventional chemical and physical methods is a costly process, while replacing some critical steps in physiochemical remediation with self-sustaining bioremediation agents are expected to be cost-effective and environmentally friendly implementation. In this study, a microalga isolated from a freshwater stream receiving treated textile wastewater was identified up to its molecular level and investigated its ability to tolerate and remove hexavalent chromium from extremely acidic conditions under different temperatures. The ability of microalgae to tolerate and remove Cr(VI) was investigated by growing it in BG11 media with different pH (1, 2, 3 & 7), amended with several concentrations of Cr(VI) and incubated under different temperatures for 96 hrs. Microalga was identified as Chlorella vulgaris and found that the isolated strain has a higher hexavalent chromium removal potential in extremely acidic conditions than in neutral pH conditions at 25 C. In contrast, its Cr(VI) removal potential is significantly influenced by the pH and temperature of the growth medium. Furthermore, it exhibited a permanent viability loss at extreme acidic conditions (pH 1 3) and prolonged exposure to the higher chromium content. The microalga investigated will be a highly useful bioagent in hexavalent chromium remediation in high acidic conditions.
Sol–Gel Immobilized Optical Microalgal Biosensor for Monitoring Cd, Cu and Zn Bioavailability in Freshwater
(Springer Nature, 2024) Rathnayake, I. V. N.
While analytical measurements provide the quantitative estimation of the total amount of metals present in a sample, they do not reflect the truly bioavailable fraction of metal which reflects the adverse biological effect. Hence the development of monitoring tools for detecting bioavailable toxic metals has become a priority in environmental monitoring activities. An optical whole-cell biosensor was constructed using the microalga Scenedesmus subspicatus MM1 immobilizing in inorganic silica hydrogels using the sol-gel technique to detect bioavailable Cadmium (Cd2+), Copper (Cu2+) and Zinc (Zn+) in freshwater. Conditions for optimum biosensor performance have been established regarding effective pH range, cell density, exposure time, and storage stability. The optimum response for the biosensor was dependent on the pH of the matrix, cell concentration and exposure time were derived. The biosensor was operational for four weeks. The limit of detection for the algal biosensor was determined as 9.0 × 10−1, 9.1 × 10−1, and 8.8 × 10−1 mg/L for Cd, Cu and Zn, respectively. Whole-cell cell biosensor will be highly useful since it comprises a single microalgal species able to detect the bioavailable content of Cd2+, Cu2+, and Zn2+ in freshwater.
Staphylococcus edaphicus KCB02A11 incorporated with natural adsorbents: first report on its tolerance and removal of hexavalent chromium [Cr(VI)]
(2023) Aththanayake, A. M. K. C. B.; Rathnayake, I. V. N.; Deeyamulla, M. P.; Megharaj, Mallavarapu
Deteriorating the quality of different parts of the ecosystem due to toxic metals is a serious global issue. Hexavalent chromium is a metal that can cause adverse effects on all living beings, including plants, animals, and microorganisms, on exposure to high concentrations for prolonged periods. Removing hexavalent chromium from various types of wastes is challenging; hence the present study investigated the use of bacteria incorporated with selected natural substrates in removing hexavalent chromium from water. Isolated Staphylococcus edaphicus KCB02A11 has shown higher removal efficiency with a wide hexavalent chromium range (0.025-8.5 mg/L) within 96 h. Incorporating the isolated strain with natural substrates commonly found in the environment (hay and wood husk) showed high removal potential [100% removal with 8.5 mg/L of Cr(VI)], even within less than 72 h, with the formation of biofilms on the used substrates applied for metal removal on a large scale for prolonged periods. This study is the first report investigating hexavalent chromium tolerance and removal by Staphylococcus edaphicus KCB02A11.
Study of chemical composition and microbial content of bulk depositions of selected sites in Gampaha district
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Navarathne, W. R. M. H. P.; Deeyamulla, M. P.; Rathnayake, I. V. N.
Wet atmospheric deposition, a natural primary scavenging process, removes organic and inorganic pollutants from the atmosphere. Significant variations in this process are observed depending on geographic conditions and anthropogenic factors. There is considerable research interest in the composition of atmospheric depositions, as it is important to decide the extent of atmospheric pollution and to predict the atmospheric quality of a selected area. However, in Sri Lanka, fewer previous studies have been reported on the chemical composition and microbial content of rainwater. In this study, three sites; Kerawalapitiya (Site A), University of Kelaniya (site B), and Keragala (Site C-control site), were selected from Gampaha district to investigate the chemical and microbial parameters of rainwater from November 2021 to March 2022. The bulk precipitation was analyzed for pH, conductivity, cations (Na+, Ca2+, NH4+, K+, Mg2+), anions (NO3-, SO42-, Cl-, Br-, F-) using ion chromatography and trace metal elements (Mg, Al, Zn, As Fe, Ni, Pb, Cu, Mn, Cr, Co, Cd) using Inductively coupled plasma-mass spectrophotometer. The pH range of all considered events was 5.98-7.31(±0.4). Volume Weighted Average (VWA) conductivity was 120, 72 and 55, respectively in sites A, B, and C. The highest VWA conductivity was observed in Kerawalapitiya. Although there were differences in the order of ions, Na+ and Ca2+ can be mentioned as the dominant cations in all the sites except in Keragala, where NH4+ was the dominant cation. Further, SO42-, Cl-, and NO3- can be mentioned as dominant anions in the selected sites. VWA of trace metal elements showed that the most abundant metal in all the sites was Mg, followed by Al and Zn. Co and Cr metal concentrations were comparatively the lowest in all three sites. The highest neutralization potential was associated with Na+, Ca2+ and NH4+ in sites A, B, and C, where the neutralization factors were 1.396, 0.655 and 0.310, respectively. Furthermore, the One -way ANOVA test revealed that there were significant differences in bacterial and fungal contents between all three sites (pbacteria= 0.000, pfungi = 0.027, ɑ=0.05).
Whole cell microalgal-cyanobacterial array biosensor for monitoring Cd, Cr and Zn in aquatic systems
(Water Science and Technology, 2021, 2021) Rathnayake, I. V. N.; Munagamage, T; Pathirathne, A.; Megharaj, M.
Bioavailable content of metals in aquatic systems has become critical in assessing the toxic effect of metals accumulating in the environment. Considering the need for rapid measurements, an optical microalgal-cyanobacterial array biosensor was developed using two strains of microalgae, Mesotaenium sp. and a strain of cyanobacteria Synechococcus sp. to detect Cd2+, Cr6+ and Zn2+ in aquatic systems. Microalgal and cyanobacterial cells were immobilized in a 96-well microplate using sol-gel method using silica. Optimum operational conditions for the biosensor array such as exposure time, storage stability, pH, and multiple metal effect were tested. A 10 min exposure time yielded optimum fluorescence values. Metal toxicity increased with decreasing pH, resulting in low relative fluorescence (%) and decreased with increasing pH, resulting in higher relative fluorescence (%). The optimum storage time for biosensor strains were 4 weeks for microalgal cultures and 8 weeks for cyanobacterial culture, at 4 °C storage temperature. The metal mixtures showed less effect on the inhibition of relative fluorescence (%) of microalgal/cyanobacterial cultures, displaying an antagonistic behavior among the metals tested. As a single unit, this photosynthetic array biosensor will be a valuable tool in detecting multi-metals in aquatic systems.