The strains of clostridia genus are very common for butanol synthesis whereas their yield and productivity varies. Basically, strains of this genus are spore­forming, rod-shaped, obligate anaerobes, and Gram-positive bacterium. Broadly, the number of species of this genus (such as C. acetobutylicum, C. beijerinckii, C. saccharoperbutylacetonicum, Clostridium saccharoacetobutylicum, Clostrid­ium aurantibutyricum, Clostridium pasteurianum, Clostridium sporogenes, Clos­tridium cadaveris, Clostridium tetanomorphum) are found with the capability for synthesizing butanol. Although, C. acetobutylicum, C. beijerinckii, C. saccharo — perbutylacetonicum, and C. saccharoacetobutylicum have shown significant activity [4]. C. acetobutylicum was the first isolated and patented bacteria for butanol production, later this strain was used for industrial scale ABE fermentation from sugars and cereal grains [45]. Earlier, it was believed that C. acetobutylicum was the only species involved in ABE fermentation. Shortly (1990s), on the basis of 16S rRNA gene sequencing and DNA fingerprinting, it was observed that there were four species in this mixed culture, namely C. acetobutylicum, C. beijerinckii, C. saccharoperbutylacetonicum, and C. saccharoacetobutylicumm [13, 45-47].

The selection of the strains for biobutanol production depends on type of feedstock, productivity required additional nutrients needed, and bacteriophage and butanol resistance. More number of attempts are needed to isolate novel organism for better yield and productivity and to modify the isolated strains applying genetic engineering.