In Vitro and in Vivo Roles of Cyanobacterial Carbonic Anhydrase as a Biomarker for Monitoring Antibiotics

Environmental biomarkers represent an emerging tool in environmental monitoring by measuring variations in cellular or molecular exposure to chemical pollutants. Carbonic anhydrase, a widespread enzyme in organisms, has the potential to be utilized as a biomarker because of its sensitive activity to chemical pollutants. Here, we report the first extracellular carbonic anhydrase (EcaA) from cyanobacteria as a biomarker for monitoring antibiotics. A recombinant microbial factory that is capable of heterologously overexpressing EcaA was constructed, and the purified enzyme exhibited superior performance in monitoring various antibiotics in vitro. The IC50 values of the four selected antibiotics, ciprofloxacin, spectinomycin, tetracycline and ampicillin, were 1.45 ± 0.61, 10.40 ± 0.34, 18.92 ± 2.42 and 59.73 ± 2.56 μM, respectively. The feasibility of EcaA as a biomarker for monitoring antibiotics in vivo was also confirmed. Growth of wild-type cyanobacteria was more inhibited by ciprofloxacin and tetracycline than an EcaA-null mutant, demonstrating that EcaA responded physiologically to the two antibiotics, thus causing growth defects. Our results enable advanced development and optimization of carbonic anhydrase as a biomarker to monitor antibiotics in vitro and in vivo.