Biodegradation of levofloxacin by an acclimated freshwater microalga, Chlorella vulgaris

Abstract

The extensive contamination of levofloxacin (LEV) in aquatic ecosystems has attracted increasing attention because of the potential for development of bacterial resistance and its eco-toxicity to non-target organisms. Biodegradation of LEV was significantly improved upon the acclimation of a freshwater microalga, Chlorella vulgaris and in the presence of elevated salinity. Among the six wild species (Chlamydomonas mexicana, Chlamydomonas pitschmannii, Chlorella vulgaris, Ourococcus multisporus, Micractinium resseri, Tribonema aequale), C vulgaris showed the highest removal capacity (12%) of LEV at 1 mg L-1. The acclimated C vulgaris, which was pre-exposed to 200 mg L-1 of LEV for 11 days, exhibited enhanced removal of 1 mg LEV L-1 by 16% after 11 days of cultivation. The addition of 1% (w/v) sodium chloride into the microalgal media significantly improved LEV removal by > 80% in the C vulgaris culture. The bioaccumulation of LEV at day 11 in C vulgaris cells without NaCI was 34 rg g-1, which was elevated to 101 mu g g(-1) LEV at 1% NaCl. The bioconcentration factor for LEV was 34 and 1004 in 0 and 1% NaCl, respectively. The mass balance analysis of LEV showed that more than 90% of LEV was biodegraded by C vulgaris at day 11 with the addition of 1% NaCI. These results demonstrated that the enhanced removal of LEV by salinity was mainly through bioaccumulation and subsequent intracellular biodegradation by C vulgaris cells.