Development of a novel heterologous β-lactam-specific whole-cell biosensor inBacillus subtilis

Background Whole-cell biosensors are a powerful and easy-to-use screening tool for the fast and sensitive detection of chemical compounds, such as antibiotics. beta-Lactams still represent one of the most important antibiotic groups in therapeutic use. They interfere with late stages of the bacterial cell wall biosynthesis and result in irreversible perturbations of cell division and growth, ultimately leading to cell lysis. In order to simplify the detection of these antibiotics from solutions, solid media or directly from producing organisms, we aimed at developing a novel heterologous whole-cell biosensor inBacillus subtilis, based on the beta-lactam-induced regulatory system BlaR1/BlaI fromStaphylococcus aureus. Results The BlaR1/BlaI system was heterologously expressed inB. subtilisand combined with theluxABCDEoperon ofPhotorhabdus luminescensunder control of the BlaR1/BlaI target promoter to measure the output of the biosensor. A combination of codon adaptation, constitutive expression ofblaR1andblaIand the allelic replacement ofpenPincreased the inducer spectrum and dynamic range of the biosensor. beta-Lactams from all four classes induced the target promoter P(blaZ)in a concentration-dependent manner, with a dynamic range of 7- to 53-fold. We applied our biosensor to a set ofStreptomycetessoil isolates and demonstrated its potential to screen for the production of beta-lactams. In addition to the successful implementation of a highly sensitive beta-lactam biosensor, our results also provide the first experimental evidence to support previous suggestions that PenP functions as a beta-lactamase inB. subtilis. Conclusion We have successfully established a novel heterologous whole-cell biosensor inB. subtilisthat is highly sensitive for a broad spectrum of beta-lactams from all four chemical classes. Therefore, it increases the detectable spectrum of compounds with respect to previous biosensor designs. Our biosensor can readily be applied for identifying beta-lactams in liquid or on solid media, as well as for identifying potential beta-lactam producers.