International Research Symposium on Pure and Applied Sciences (IRSPAS)

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Author: search.filters.author.Manage, P.M.Subject: search.filters.subject.Degradation

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    Bacterial degradation of tetracycline (TET) by TET resistant bacteria; A green solution for antibiotic pollution.
    (4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Liyanage, G. Y.; Manage, P.M.
    Tetracyclines (TET) have been extensively used in aquaculture for chemotherapy against various fish diseases such as fin rot, skin ulcers. Overuse and misuse of antibiotics are widely regarded as two of the major factors promoting antibiotic resistance. Resistance to TET occurs via two primary mechanisms; ribosomal protection and enzyme inactivation. To minimize the development of resistance, excess amount of TET should be removed from the aquatic environment. Therefore, studies on the biodegradability of TET can be taken as a very first step of an environmental risk assessment. The present study reports the biodegradation of TET by Enterobacter sp., Micrococcus luteus, Enterobacter ludwigii, Bacillus sp. and Streptomyces sp., which were isolated as TET resistance, non-pathogenic bacteria. In a previous study, TET resistant bacterial isolates were identified using the 16s rRNA sequencing. Overnight bacterial cultures grown in a medium without TET, were introduced into a medium containing TET at final concentration of 5 μg/ml. Triplicate samples were incubated at 28 °C with shaking at 100 rpm under dark conditions. Subsamples (0.5 ml) were removed at 2 days interval for a period of 14 days. Remaining TET in the subsamples was analyzed using High Performance Liquid Chromatography (HPLC). Complete degradation of TET by M. luteus and E. ludwigii was detected at the end of 14 days of incubation. Descending degradation percentages were followed by Enterobacter sp. (74%), Streptomyces sp. (72%) and Bacillus sp. (70%) at 14 days, respectively. Lowest half-life time of TET was shown by M. luteus and E. ludwigii (6 days), whereas half-life time of 8 days, 11 days and 12 days were recorded for Enterobacter sp, Streptomyces sp. and Bacillus sp., respectively. According to the degradation results obtained, it can be concluded that the selected bacterial strains can be used as potential candidates to be introduced into wastewater effluents to remove TET in effluent water, before reaching natural environments
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    Isolation of laccase producing fungi: Aspergillus niger from Sri Lankan textile wastewater effluents and its potential applicability on decolorization of an azo dye: CI Direct Blue 201
    (4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Ekanayake, E. M. M. S.; Wijesekara, I.; Manage, P.M.
    The complex aromatic structural nature of synthetic dyes show resistance to natural oxidation processes and persist in the surface water and sediments for a long time. The existing physical and chemical treatment methods are costly and create secondary pollution. Therefore, the present study was focused on the degradation of an azo dye: CI Direct Blue 201 (DB 201), by myco-remediation. Aspergillus niger, a filamentous fungus, was isolated from textile wastewater effluent site in Sri Lanka and pure cultures were maintained on Potato Dextrose Agar (PDA) plates. Four cylinders (10 mm diameter in each) of actively growing A. niger cultures were cut and inoculated into mineral salt medium consisted of 50 mgL-1 DB 201 dye. All the experiments were carried out in triplicates, while controls were maintained without addition of the fungus. Flasks were incubated at 28 °C for seven days with shaking at 100 rpm. Three milliliters of sample aliquots were removed at 6 hrs intervals, centrifuged and the changes of the absorbance in the supernatant was analyzed through UV-Vis spectrophotometer at 570 nm. The laccase activity was determined by measuring the increase in the optical density at 420 nm. The reaction mixture for laccase assay contained 5 mM of 2,20-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) in 50 mM sodium acetate buffer (pH 4.5) and 50 μL of decolorized dye solution (ε420 = 36000 M−1 cm−1). Decolorized dye sample was analyzed through Fourier Transform Infrared (FTIR) Spectroscopy. A Bio-sorption test was carried out by providing the same incubation conditions using 3-day-old live and autoclaved fungi. The control without adding fungus, remained the same without showing any decolorization. The enzyme activity of laccase has increased during the decolorization processes from 18 Uml-1 to 254 Uml-1. The changes of the FTIR spectra relevant to the N=N Vibration (1723.3 cm-1), S=O Stretching (1227.3 cm-1) and N-O Stretching (742.88 cm-1) indicated the changes of the initial DB 201 dye structure after the treatment by A. niger. Furthermore, the bio-sorption assay by live (100%) and autoclaved fungi (12 ± 2%) confirmed the decolorization and the degradation of DB 201 dye would be based on the metabolic activity of the fungus rather than surface adsorption. Therefore, the present study emphasizes the potency of A. niger as an eco-friendly candidate for degradation of azo dyes. Further studies regarding the application of enzymes for real textile dye treatments are currently in progress.