Detection and analysis of Bacillus subtilis growth with piezoelectric quartz crystal impedance based on starch hydrolysis

A piezoelectric quartz crystal (PQC) impedance method based on the alpha-am ylase-catalyzed hydrolysis of starch:present in a culture medium has been d eveloped for in situ monitoring of the whole growth process of Bacillus sub tilis and the variation in the activity of alpha-amylase during bacterial g rowth. An S-shaped response behavior was observed for Delta f(0), and simul taneously inverse S-shaped responses were found for Delta R-1 and Delta L-1 . The ratio of Delta R-1 to Delta f(0) or Delta L-1 coincided well with tha t calculated from Martin's equations reflecting the solution density-viscos ity effect, suggesting that the continuing change in liquid loading onto th e PQC surface causes significant variation in Delta f(0), Delta R-1, and De lta L-1. Bacterial growth equations were derived from-the kinetics of the e nzyme-catalyzed hydrolysis of starch, which fit well with the experimental responses of Delta f(0), Delta R-1, and Delta L-1. Kinetic parameters of ba cterial growth, including the asymptote (A), the maximum specific growth ra te (mu(m)), and the lag time (lambda), were obtained and were in good agree ment with those obtained from the pour plate count method. The variation in the activity of alpha-amylase exhibited peak-type behavior with its maximu m value at the later stage of the log phase. In addition, the influence of initial bacterial concentration was also investigated. (C) 2000 Academic Pr ess.