Abstract
The study of growth of Lactococcus lactis NCIM 2114, a nisin producer, was modeled using continuously generated concentration data for growth in fermenter. The sigmoidal growth functions, Logistic, Gompertz, and Richards were used to fit the data. A nonlinear regression method was used to fit the data and estimate growth parameter values of L. lactis, using Marquardt algorithm with Statistical Software SPSS, version 20. Bacterial growth data from the exponential phase of the bacteria’s growth was analyzed. An F test showed that the Gompertz and Logistic functions were acceptable 92% and 67% of times respectively in the batch fermenter runs where this particular application was used to derive the lag time, growth rates, and time to maximum growth rates of L. lactis. The maximal specific growth rate ranged between 0.23 h−1 to 0.30 h−1 and the lag time lasted up to a maximum of 1.63 h depending upon aeration conditions provided to the organism. This study will help to estimate specific growth rates and lag time of L. lactis under different growth conditions. Predicted values can be accurately determined.
Highlights
The growth of an organism in a growth medium can be monitored by measuring absorbance, cell biomass (BM as cell dry weight) or cell counts per unit cell volume
Because the Gompertz function is a general deterministic model used with differential equations at constant temperature [9], it was used most successfully to determine lag time (λ) and specific growth rate maxima μm of the organism [3]
Of the two three-parameter functions used, the Gompertz function showed a higher acceptance (92%), to model the growth of L. lactis, than the Logistic function (67%), when each was compared to the four-parameter Richards function on fd values (Table 3)
Summary
The growth of an organism in a growth medium can be monitored by measuring absorbance, cell biomass (BM as cell dry weight) or cell counts per unit cell volume. Modified equations for bacterial growth can be derived for conditions to determine the lag time and growth rate of an organism. There was no nutrient limitation in the medium for growth of L. lactis This organism produced nisin as a primary metabolite [8]. The maximum specific growth rate of the organism and lag time to enter exponential growth was determined under the different levels of agitation and aeration. Because the Gompertz function is a general (dynamic) deterministic model used with differential equations at constant temperature [9], it was used most successfully to determine lag time (λ) and specific growth rate maxima μm of the organism [3]. Our results point to the acceptability of Gompertz function as compared to Logistic function
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