The security and scarcity of clean water resource for the safe livelihoods of human beings are of growing concerns worldwide. It has become more critical due to the contamination of water resources by various pharmaceutical contaminants (PCs). These chemicals can be transported through the atmosphere and water and, in many cases, find their way into sediments and soils. Moreover, multidrug resistance efflux pumps are present in all organisms and can exist in large numbers within a single microorganism. Low concentrations of PCs may be beneficial for the bacteria through triggering specific transcriptional changes that are independent of the bacterial stress response pathways, especially antibiotics, which can develop the resistance of bacteria. Microalgae mediated bioremediation of PCs have recently gained scientific attention due to their wide distribution, mixotrophic capabilities, role in the fixation and turnover of carbon, and their recovered biomass for the production of bioenergy. In this study, the biodegradation and metabolic fate of levofloxacin (LEV) via a microalga, Scenedesmus obliquus in synthetic saline wastewater were investigated in this study. LEV removal (1 mg L−1) by S. obliquus was relatively low in the synthetic wastewater without the addition of sodium chloride (NaCl); however, its removal increased significantly from 4.5 to 93.4% with increasing of its salinity from 0 to 171 mM NaCl. Kinetic studies showed that the removal rate constant (k) increased from 0.005 to 0.289 d−1 and degradation half-life decreased from 272 to 5 d in the presence of NaCl (0-856 mM). The removal mechanism analysis showed that the major mechanism of NaCl mediated enhancement of LEV removal was the bioaccumulation and subsequent intracellular biodegradation of LEV in microalgal cells. Six metabolites were identified via gas chromatography-mass spectrometry analysis after biodegradation of LEV. A metabolic pathway was postulated with regard to various cellular biocatalytic reactions in S. obliquus, including decarboxylation, demethylation, dehydroxylation, side chain breakdown, and ring cleavage.

Biodegradation and metabolic fate of levofloxacin via a freshwater green alga, Scenedesmus obliquus in synthetic saline wastewater

254th National Meeting (2017)

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