Course of fermentations carried out with C. acetobutylicum DSM 1731 and milled corn as substrate was similar to that referred for C. acetobutylicum ATCC 824 (Lee S. Y. et al., 2008) i. e. it was characterized by distinct metabolic phases, reutilization of acids during solventogenesis and development of hydrogen that peaked during acidogenesis. According to Johnson et al., (1997), C. acetobutylicum DSM 1731 showed 96% DNA sequence similarity with C. acetobutylicum ATCC 824. The so-called acid crash i. e. the state when the fermentation finished in acidogenic step was sometimes observed from unclear reason, using this strain and milled corn as substrate (Rychtera et al., 2010). Unfortunately, intracellular level of formic acid was not determined and therefore it was not proved or disproved whether acid crash in these cases was also caused by formic acid (Wang et al., 2011).

The strain C. beijerinckii CCM 6218 should be identical with the strain C. beijerinckii ATCC 17795 according to data of Czech Collection of Microorganisms. Surprisingly, if the strain C. beijerinckii ATCC 17795 was tested for butanol production using molasses cultivation medium (Shaheen et al., 2000), both yield and maximum butanol production was low, 10% and 6.1 g. L-1, respectively. In addition this strain together with C. pasteurianum NRRL B-598 showed different fermentation pattern in comparison with C. pasteurianum NRRL B-598 and butanol production initiation started during exponential growth phase. The strain also metabolized substrate, saccharose, faster than both other tested strains what was reflected in higher productivity of butanol.

The strain Clostridium pasteurianum NRRL B-598 used in this study differed significantly in some physiological traits from both the species characteristics published in Bergey’s Manual of Systematic Bacteriology (Rainey et al., 2009). Although strains of the species C. pasteurianum are known rather as acetic and butyric acids or hydrogen producers (Rainey et al., 2009; Heyndrickx et al., 1991), the strain C. pasteurianum NRRL B-598 was cited in US Patent No 4539293 as butanol producing when used in mixture with further acidogenic strain e. g. C. butylicum. Unfortunately precise cultivation conditions, yields, solvents concentrations and other data are not available in the mentioned patent.