A d,l-lactate biosensor based on allosteric transcription factor LldR and amplified luminescent proximity homogeneous assay

Lactate, a hydroxycarboxylic acid commercially produced by microbial fermentation, is widely applied in diverse industrial fields. Lactate exists in two stereoisomeric forms (d-lactate and l-lactate). d-Lactate and l-lactate are often simultaneously present in many biological samples. Therefore, a biosensor able to detect both d- and l-lactate is required but previously unavailable. Herein, an allosteric transcription factor LldR from Pseudomonas aeruginosa PAO1, which responds to both d-lactate and l-lactate, was combined with amplified luminescent proximity homogeneous assay technology to develop a d,l-lactate biosensor. The proposed biosensor was optimized by mutation of DNA sequence in binding site of LldR. The optimized biosensor BLac-6 can accurately detect the concentration of lactate independent on ratio of the two isomers in pending test samples. The biosensor was also tentatively used in quantitative analysis of d-lactate, l-lactate, or d,l-lactate in fermentation samples produced by three recombinant strains of Klebsiella oxytoca. With its desirable properties, the biosensor BLac-6 may be a potential choice for monitoring the concentration of lactate during industrial fermentation.