Acute impact of tetracycline and erythromycin on the storage mechanism of polyhydroxyalkanoates

•Tetracycline and erythromycin increased polyhydroxyalkanoates storage.•Antibiotics severely affected internal utilization of polyhydroxyalkanoates.•Impaired oxygen balance was attributed to substrate binding mechanism.•Inhibitory effects should be evaluated considering growth and storage mechanisms.

The study investigated acute impact of tetracycline and erythromycin on substrate storage under aerobic conditions. A fill and draw reactor fed with peptone mixture was maintained at steady-state at a sludge age of 10 days; the acclimated biomass was used in a series of batch runs. The first run served as control reactor with organic substrate alone and the others were started with antibiotic doses of 50 mg/L and 200 mg/L for assessing intracellular storage. Parallel batch reactors were also conducted for recording oxygen uptake rate profiles. Both antibiotics enhanced substrate storage, leading to higher levels of polyhydroxyalkanoates incorporated into biomass, but they impaired its internal utilization for microbial growth. The observed decrease in oxygen consumption under the acute effect of antibiotics could partially be related to substrate storage – except for 50 mg/L of erythromycin dosing – suggesting an additional substrate binding mechanism by antibiotics, leading to residual biodegradable substrate.