Study On Microbial Growth Model Based On Metabolites

As one of the key technologies driving human development in the 21st century,microorganisms are continuously applied in the fields of environmental management,fermentation industry,medical health,etc.The microbial growth kinetics model including Logistic,Gompertz,Schunte,Lopz models quantitatively describes microbial growth in mathematical form.These models describe the corresponding relationship between biomass and growth time.These models have been applied to detection methods whose results are linearly related to the number of microbial,such as plate colony counting,PCR,biochip technology,and microcalorimetry.However,for some metabolites that are continuously accumulated during the growth process,such as oxygen consumption,viscosity,electrical impedance,etc.,there is still no corresponding kinetic model that can describe the relationship between biomass and growth time and give the microbial growth parameters.So,this paper studied the S-shaped curve described by Logistic model,Gompertz model,Baranyi model and Huang model,and analyzed the influence of various parameters on the model.The possibility that existing models can be directly used for microbial growth studies in metabolite methods has also been discussed.The study found that the three parameters:the maximum growth amount,the maximum growth rate,and the lag time have the same effect on different models,the increase in their values corresponds to the maximum value of the model,the slope of the inflection point,and the increase in the tangent of the inflection point and the focus of the coordinate axis.However,in the models mentioned above,the Logistic model and the Gompertz model has only three stages?the lag phase,the exponential growth phase and the stationary phase?owing to their mathematical equations,and the Baranyi model has central symmetry points,so these three models are not suitable for direct description of metabolites.Only the curve described by the Huang model has the possibility of corresponding to the metabolite curve.But further research found that the description of Huang model of microbial death is not in line with the actual situation.Therefore,taking the four stages of microbial growth as the premise,starting from the definition of each parameter in the microbial growth model,and referring to the Huang model,a new metabolite-based microbial growth kinetics model is proposed in this paper.This model is used to describe the cumulative product of the metabolites,and obtain the growth parameters such as the lag phase,the maximum growth rate,and the death rate of the microorganisms.The parameters in the newly established model are verified according to the four models mentioned.Combining the fitted image and taking the absolute value of the relative error,the estimated standard error,and the root mean square error as the evaluation parameters,this paper verified the application of the new model in actual measurement.The CO₂ produced during the growth of Staphylococcus aureus and yeast was used as an indicator of metabolites in the experiment.The comparison results show that the Gompertz model is more suitable than the Logistic model and the Baranyi model for the S-shaped growth curve with obvious asymmetry of the curve,but the opposite is true for the curve with symmetric center curve.However,the Huang model and the newly established model do not have such preference,and show good goodness of fit and very small fitting error for both curves.For the fitting of the Huang model to Staphylococcus aureus,the MARE was0.064,the SEP was 47.217,and the RMSE was 0.057.And for the fitting of the Huang model to yeast,the MARE was0.055,the SEP was 26.769,and the RMSE was 1.0378.For the fitting of the new established model to Staphylococcus aureus,the MARE was 0.039,the SEP was 35.985,and the RMSE was 0.05.And for the fitting of the Huang model to yeast,the MARE was 0.042,the SEP was 14.302,and the RMSE was 0.012.The experimental results show that the new model can better express the measurement results when the metabolic products are accumulated during the growth of microorganisms.Finally,the paper measured the growth kinetics of Staphylococcus aureus,Candida albicans and yeast at 25 degrees Celsius.Moreover,the effect of temperature on microbial growth was studied in the range of 24-34 degrees Celsius.The results show that in this temperature range,the increase in temperature can increase the maximum growth rate and reduce the length of the lag phase,but after exceeding the optimum growth temperature,the maximum growth rate will be decreased.And this result is also consistent with the literature.In this paper,a new metabolite-based microbial growth kinetics model was established,and the goodness of fit of the model was verified by taking CO₂ as an example of metabolite.The newly established model can be used to fit the growth of microorganisms under different environmental conditions such as temperature and pH,and obtain the complete microbial growth curve and the growth parameters of various stages of the microorganism in metabolite measurement methods.