Activity of the enzyme system in thermally killed Bacillus cells

Abstract

Bacillus subtilis and Bacillus licheniformis 7B were killed by exposure to isothermal dry heat in the temperature range 160-280°C. The exposure time required to completely kill an entire cell population varied from 30 to 2.5 min. The enzyme system in the dead cells was found to remain viable and active as shown by its oxidation characteristics for lactic, formic, and glutamic acids. The oxidation kinetics followed the Michaelis-Menten rate equation incorporating the effect of pH described by one of the Michaelis pH functions based on the protonation and deprotonation of the active sites of the enzymes. The activity of the enzyme system in these dead cells was observed to be comparable with that of the living cells. Better enzymatic activity was obtained with higher temperature exposure corresponding to a shorter dead time. A higher oxidation rate was observed under conditions facilitating the diffusion of the substrates through the cell membranes. These results are significant to bioprocessing and biosensor fabrication since dead cells with their enzyme systems remaining viable and active are relatively free from maintenance and control of the growth environment which is often necessary when living cells are used. They also have the advantage of enzyme protection by the cell membrane over the purified enzymes.