Biodegradation of cephalexin in wastewater by Glutamicibacter sp. S2 and Herbaspirillum sp. S8: Performance, pathway, genomes and synergistic bio-augmentation

Microbial degradation of β-lactams is an effective bioremediation method. In the present study, Glutamicibacter nicotianae S2 and Herbaspirillum seropedicae S8, capable of effectively biodegrading cephalexin are isolated from untamed activated sludge. Culture parameters are optimized by response surface methodology: 5 % (v/v) dosage, pH 7.5 around, and 30 °C; achieving the maximum cephalexin removal of 84.12 % (S2) and 82.35 % (S8) ultimately. S2 has an excellent ability for biotransformation, while S8 removes cephalexin mainly by adsorption at high initial concentrations. Enzymatic assays reveal that both functional strains are able to produce β-lactamase and the addition of a co-substrate significantly increased the dehydrogenase activity. Combined with whole genome sequencing and LC-Q-TOF-MS analysis of degradation products, genes associated with ring opening hydrolysis, demethylation, and deamination may be involved in the biotransformation of cephalexin. Moreover, twelve possible biodegradation products are identified and three biodegradation pathways are proposed. Based on the identification of main biodegradation byproducts and the biotoxicity assessment using the ecological structure–activity relationship (ECOSAR) model, applying the microbial consortia constructed by the two functional strains achieves significant synergistic degradation effects, with markable enhancement of cephalexin and TOC removal and a substantial increase in biomass. The different mechanisms of resistance to cephalexin in S2 and S8 are analyzed in-depth, and the synergistic bio-augmented innovative approach of “adsorb storage-degrade conversion” and its potential mechanism are proposed for the first time. Overall, this study is the first to describe a detailed cephalexin degradation mechanism of single functional strains and microbial consortia. This will provide new insights into the bioremediation of β-lactam antibiotic wastewater and broad a wide range of prospects in the field of popularizing and applying bioaugmentation wastewater treatment technologies.