Dynamics of microbial growth in single substrate culture

In this study the results of continuous to batch mode experiments conducted to characterize the initial transient response of carbon limited microbial cells growing in a chemostat to a pulse of the growth limiting substrate are presented. Changes in cellular rates of growth, substrate uptake, carbon dioxide evolution, and organic carbon excretion were recorded for three different preculture conditions. To ensure the validity of the data, ninety percent of added carbon was accounted for in generated biomass, evolved carbon dioxide, and in excreted organic products before and after the substrate pulse.; The continuous shifts revealed that values of growth and respiration were proportional to the preculture dilution rate while the capacity to increase the respiration and growth rate was inversely proportional to the preculture dilution rate. Saturation of respiration and biosynthetic capacity led to a high amount of excretion at the intermediate and highest preculture dilution rates tested. Only the highest preculture dilution rate was able to utilize the excreted carbon before the specific carbon dioxide evolution rate fell considerably due to lack of substrate.; The identity of the biosynthetic growth limitation was also explored in this study using similar continuous to batch shift experiments. Evidence was found to support the hypothesis that the biosynthetic limitation is an amino acid supply limitation and not a protein production capacity limitation. Continuous to batch mode shifts followed by a pulse of growth limiting carbon substrate show the transient response of the biosynthetic enzyme glutamate dehydrogenase qualitatively matched the transient response of the intracellular RNA concentration suggesting the enzyme was more likely to be the cause of the biosynthetic growth limitation rather than the intracellular ribosome concentration.