Diclofenac (DCF), a non-steroidal anti-inflammatory drug (NSAID) and sulfamethoxazole (SMX), an antimicrobial agent, are in common use and can be often detected in the environment. The constructed wetland systems (CWs) are one of the technologies to remove them from the aquatic environment. The final effect of the treatment processes depends on many factors, including the interaction between plants and the plant-associated microorganisms present in the system. Bacteria living inside the plant as endophytes are exposed to secondary metabolites in the tissues. Therefore, they can possess the potential to degrade aromatic structures, including residues of pharmaceuticals. The endophytic strain MG7 identified as Microbacterium sp., obtained from root tissues of Phalaris arundinacea exposed to DCF and SMX was tested for the ability to remove 2 mg/l of SMX and DCF in monosubstrate cultures and in the presence of phenol as an additional carbon source. The MG7 strain was able to remove approximately 15% of DCF and 9% of SMX after 20 days of monosubstrate culture. However, a decrease in the optical density of the MG7 strain cultures was observed, caused by an insufficient carbon source for bacterial growth and proliferation. The adsorption of pharmaceuticals onto autoclaved cells was negligible, which confirmed that the tested strain was directly involved in the removal of DCF and SMX. In the presence of phenol as the additional carbon source, the MG7 strain was able to remove approximately 35% of DCF and 61% of SMX, while an increase in the optical density of the cultures was noted. The higher removal efficiency can be explained by adaptive mechanisms in microorganisms exposed to phenol (i.e. changes in the composition of membrane lipids) and by a co-metabolic mechanism, where non-growth substrates can be transformed by non-specific enzymes. The presence of both DCF and SMX and the influence of the supply frequency of CWs with the contaminated wastewater on the diversity of whole endophytic bacterial communities were demonstrated. The results of this study suggest the capability of the MG7 strain to degrade DCF and SMX. This finding deserves further investigations to improve wastewater treatment in CWs with the possible use of pharmaceuticals-degrading endophytes.
Keywords: biodegradation; constructed wetlands; diclofenac; endophytic bacteria; sulfamethoxazole.
© 2018 Anna Węgrzyn and Ewa Felis.