RESUMEN
Physiological changes in populations of Clostridium beijerinckii and Clostridium tetanomorphum were monitored by fluorescence staining and flow cytometry. To estimate the number of metabolically active cells in exponential growth, a combination of the dyes propidium iodide and carboxy fluorescein diacetate appeared to be a good choice for both species. During stationary phase, these stains did not reflect physiological changes sufficiently and therefore additional labeling with bis-(1,3-dibutylbarbituric acid) trimethineoxonol was applied. Results of fluorescence staining in solventogenic batch fermentations were compared with substrate-use data, the concentration of key metabolites and growth curves. We demonstrate that measurements by all methods were mutually compatible.