Biodegradation of sulfamethoxazole by individual and mixed bacteria

Abstract

Antibiotic compounds, like sulfamethoxazole (SMX), have become a concern in the aquatic environment due to the potential development of antibacterial resistances. Due to excretion and disposal, SMX has been frequently detected in wastewaters and surface waters. SMX removal in conventional wastewater treatment plants (WWTPs) ranges from 0% to 90%, and there are opposing results regarding its biodegradability at lab scale. The objective of this research was to determine the ability of pure cultures of individual and mixed consortia of bacteria (Bacillus subtilis, Pseudomonas aeruginosa, Pseudomonas putida, Rhodococcus equi, Rhodococcus erythropolis, Rhodococcus rhodocrous, and Rhodococcus zopfii) known to exist in WWTP activated sludge to remove SMX. Results showed that R. equi alone had the greatest ability to remove SMX leading to 29% removal (with glucose) and the formation of a metabolite. Degradation pathways and metabolite structures have been proposed based on the potential enzymes produced by R. equi. When R. equi was mixed with other microorganisms, a positive synergistic effect was not observed and the maximum SMX removal achieved was 5%. This indicates that pure culture results cannot be extrapolated to mixed culture conditions, and the methodology developed here to study the biodegradability of compounds under controlled mixed culture conditions offers an alternative to conventional studies using pure bacterial cultures or inocula from activated sludge sources consisting of unknown and variable microbial populations.

Biodegradation of sulfamethoxazole: current knowledge and perspectives

“…Although exploratory and conducted using high initial SMX concentrations, these studies illustrate that certain Larcher and Yargeau (2011) MMSM minimum mineral salt medium types of bacteria may possess greater SMX-degrading capabilities. Rhodococcus sp.…”

“…(Bouju et al 2012). Batch experiments were also conducted using pure bacterial cultures in an aqueous matrix consisting of minimum mineral salt medium in order to determine the SMXdegrading efficacy of specific bacterial strains that have been previously isolated from biological WW treatment systems (Gauthier et al 2010;Larcher and Yargeau 2011). One study focused on the ability of Rhodococcus rhodochrous and observed 20 % SMX degradation only in the presence of glucose (30 mg/L SMX+3 g/L glucose); SMX was not removed when it was the sole carbon source.…”

“…A metabolite peak was consistently detected during HPLC analysis, and based on the enzymes known to be produced by Rhodococcus sp. and R. equi, it was proposed that the most likely degradation products would be an acetylated SMX compound or its alcohol derivative (Larcher and Yargeau 2011).…”

Biodegradation of sulfamethoxazole and other sulfonamides by Achromobacter denitrificans PR1

“…Most studies on SMX biodegradation assessed its removal by activated sludge [14][15][16][17][18] and only few studies identified the bacterial strains involved in the process. The first examples were reported for members of the genus Rhodococcus, which were able to co-metabolize SMX with glucose in axenic culture [19,20]. Later, other organisms, all enriched from activated sludge, belonging to the genera Achromobacter, Ralstonia, Pseudomonas, Brevundimonas, Variovorax, Rhodococcus, and Microbacterium were reported as capable of degrading SMX [21][22][23].…”

Isolation of Bacterial Endophytes from Phalaris arundinacea and their Potential in Diclofenac and Sulfamethoxazole Degradation

“…In all three bacterial cultures, SMX was sequentially converted into 3-amino-5-methylisoxazole, 4-aminophenol, and hydroquinone. Larcher and Yargeau (2011) reported that the arylamine N-acetyltransferase, which shows high specificity for aromatic amines, is involved in the degradation of SMX in P. aeruginosa and Rhodococcus species. Hu et al (2017) proposed the pathways of SMX degradation by Enterobacter cloacae strain T2.…”