Lipid- and Multivariate-Based Analyses to Determine Cell Response to pH Variations and Buffer Composition

During marine bioprocess development, pH control is of paramount importance. In shake flasks, aerobic fermentations usually have no pH control except from the buffering effect provided by buffers in the medium. However, the use of traditional buffers, such as phosphate buffer, can lead to the precipitation of medium components. Good's buffers may be a sound alternative. Using Serratia rubidaea cells and their production of prodigiosin as model system, several Good's buffers were tested and compared to phosphate buffer. Lipidomics analysis in conjugation with statistical multivariate analysis was performed to determine the cellular response to pH variations and buffer composition. Biomass productivity was similar when using the different buffers, but prodigiosin production was highly influenced and was highest with MES buffer at pH 5.5, reaching 249.8 mg/L, which corresponds to 43.7 mg/g_biomass. At pH 7.0, the best results were achieved with EPPS, HEPES and TRIS buffer, being these good substitutes for phosphate buffer in marine medium. The results also show that cells adapted the fatty acid composition of their membranes as response to the buffering species present in the growth medium. This is a clear indication that the buffer composition should not be disregarded when developing a bioprocess.