In this presentation, we have discussed that the acetogenic thermophilic bacterium, Clostridium thermoaceticum, ferments glucose almost quantitatively to acetate. That part of the acetate is formed from CO2, which functions as the electron sink. We have demonstrated that enzymes in the acetate formation contain trace elements such as iron, cobalt, nickel, selenium and tungsten. Furthermore, we have indicated that this bacterium must have an electron transport system, which is not yet completely understood. With Clostridium thermohydrosulfuricum we have obtained results which indicate that this thermophile may selectively produce proteins dependent on the environmental temperature. We have presented a new bacterium, Thermoanaerobacter ethanolicus, which ferments several sugars including starch, cellobiose, and xylose to ethanol. We have demonstrated the existence in a thermal environment of anaerobic bacteria that grow at temperatures of around 90 degrees C and which are capable of fermenting diverse substrates such as lactate, glucose, and cellulose.