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.