**7. Conclusions**

Bioethanol production from lignocellulosic biomass with thermophilic bacteria needs robust microbes regarding several aspects. One of the main advantages of thermophilic bacteria is their broad substrate spectra with many strains capable of simultaneous pentose and hexose degradations. Additionally, some thermophiles degrade complex carbohydrates like cellulose and hemicellulose although many of these strains are not highly ethanologenic. Recent advantages in genetic engineering have improved ethanol yields, mostly by knocking out pathways of undesired end-products. On the back side is the fact that yields and ethanol tolerance as well as low tolerance for high initial substrate concentrations still limits the use of thermophiles for large scale operations. The use of stable co-cultures where on microbe hydrolyses the sugar polymers and the other one ferments the sugars released to ethanol is an attractive way to go forward but warrants further investigations.
