Most of work was performed with the strain Clostridium pasteurianum NRRL B-592 which differed from usually employed solvent producing clostridia significantly, especially in sooner onset of solvents production i. e. during exponential growth phase. The strain was also chosen because of its properties i. e. stable growth and solvents production, robustness regarding minor changes in cultivation conditions and resistance toward so-called strain degeneration. Nevertheless in some cases, other, more typical solventogenic strains, C. acetobutylicum DSM 1731 and C. beijerinckii CCM 6182 were used, too.

Compositions of cultivation media, strains maintenance, description of cultivation, used analytical methods and expressions describing calculation of fermentation parameters i. e. yield and productivity for batch, fed-batch and continuous fermentations are given in Patakova et al., (2009 and 2011a).

3.1 Methods of ABE study

Despite complex process character, fermentation control, which is of key importance, relies only on few on-line measurable values like pH or redox potential of the medium and off-line determined concentrations of substrate(s), biomass and metabolites. In order to understand the process better and to improve fermentation control, fluorescence labelling of selected traits together with microscopy and flow cytometry was applied. Flow cytometry, as high — throughput, multi-parametric technique capable of analysis of heterogenic populations at the level of individual cells, has recently been used for description of clostridial butanol fermentations for the first time, but in totally different context (Tracy et al., 2008).