A New Method for Estimating Growth Behavior of Bacterial Population under Restrictive Culture Conditions

Abstract

According to the changes in optical density ( A 600) of E. coli population in shake flask-culture and ferment culture and by using an improved data-smoothing method and then differential derivation, the two kinetic parameters, instantaneous rate ( v inst) and instantaneous increment ( v inc), as response variable were estimated and could be used to accurately characterize the kinetics of bacterial population growth. The v inst showed exponential decay pattern, while the kinetic pattern of v inc varied and depended on the inoculums size. In either case for v inst or for v inc, the kinetic curves appear neither delay period nor stable period. In fact, the pattern of kinetic growth curve were determined by the number of cells under division status, which was the result of the interaction between endogenous growth ability (which is from the continuous cell-cyclic division) and exogenous growth inhibitory force (caused by the decreased nutrients and increased metabolites). In addition, based on the dividing pattern of bacterial cell, another response variable, doubling time (Q), was also used to express the endogenous kinetic behavior. And then a bioengineering parameter, volumetric productivity, can be calculated according to the instantaneous increment ( v inc). This research can provide an effective mathematical analysis to resolve the problems of uncertainty in using logistic and Monod equation to fit the growth curve of E. coli .