Aerobic biotransformation of the antibiotic ciprofloxacin by Bradyrhizobium sp. isolated from activated sludge

Abstract

Ciprofloxacin (CIP) is an antibiotic that is widely used to treat bacterial infections and is poorly biodegraded during wastewater treatment. In this study, a CIP-degrading bacterial strain (GLC_01) was successfully retrieved from activated sludge by enrichment and isolation. The obtained bacterial strain shares over 99% nucleotide identity of the 16S rRNA gene with Bradyrhizobium spp. Results show that Bradyrhizobium sp. GLC_01 degraded CIP via cometabolism with another carbon substrate following a first-order kinetics degradation reaction. CIP degradation by Bradyrhizobium sp. GLC_01 increased when the concentration of the primary carbon source increased. The biodegradability of the primary carbon source also affected CIP degradation. The use of glucose and sodium acetate (i.e. readily biodegradable), respectively, as a primary carbon source enhanced CIP biotransformation, compared to starch (i.e. relatively slowly biodegradable). CIP degradation decreased with the increase of the initial CIP concentration. Over 70% CIP biotransformation was achieved at 0.05 mg L whereas CIP degradation decreased to 26% at 10 mg L. The phylogenetic identification and experimental verification of this CIP-degrading bacterium can lead to a bioengineering approach to manage antibiotics and possibly other persistent organic contaminants during wastewater treatment.

Ecological impact of the antibiotic ciprofloxacin on microbial community of aerobic activated sludge

“…The widespread use of CIP leads to its occurrence at relatively high concentration than others in its group. (Nguyen et al, 2018). As expected based on previous work (Larsson et al, 2007;Nguyen et al, 2017;Tran et al, 2018), Secondary effluent, hospital wastewater and pharmaceutical wastewater have been found with CIP at concentration of 10 -200 µg/L and 6.5 -31 mg/L.…”

“…Another six reactors were exposed to 50 and 500 µg/L of CIP for two months. The exposure concentrations were environmentally relevant levels in wastewater (Nguyen et al, 2018).…”

Cometabolic biotransformation and impacts of the anti-inflammatory drug diclofenac on activated sludge microbial communities

“…For instance, Terzic et al (2018) observed an increase from none to 99% removal of antibiotic macrolide after two months of exposure. Likewise, Nguyen et al (2018) retrieved a Bradyrhizobium sp. from AS via an enrichment and isolation process, which showed the ability to cometabolite antibiotic ciprofloxacin.…”

Insights into the Fate and Removal of Antibiotics in Engineered Biological Treatment Systems: A Critical Review

“…For some antibiotics of sulfonamides class (e.g., SMX and SDZ) and trimethoprim (TMP), sorption onto biological sludge plays a minor role in their removal in engineered biological treatment systems, , and therefore, biodegradation is the principal pathway for their removal. Biodegradation is a process that involves the breakdown of complex organic compounds including antibiotics either through biotransformation, resulting in formation of different metabolic intermediates (i.e., dead end and/or transitory intermediates) − or through complete mineralization to CO 2 and H 2 O ,, by pure or mixed microbial culture. The terms biotransformation and biodegradation are interchangeably used in the literature.…”

“…Different intermediates could be formed either by breakdown of the parent antibiotic compounds ,,, or by hydroxylation, acetylation of the amino group in SMX, ,− and loss of N -methyl group by demethylation of the dimethyl amino group at C4 position of TET molecule without breakdown of the parent compound. Microorganisms have the ability to degrade antibiotics utilizing them as a sole carbon and energy source and/or via cometabolism. ,, Several recent studies focused on possible biodegradation mechanisms (including intermediates, pathways, functional microorganisms, catabolic enzymes, and genes) of antibiotics in different microbial sludge systems, which are important to elucidate the fate of antibiotics in the environment. ,− The following section examines the biodegradation mechanisms of the selected target classes of antibiotics. Moreover, the biotransformation and mineralization by pure and mixed cultures under different redox conditions, intermediates, pathways, catabolic enzymes, and genes involved are also discussed.…”