Seventy years. These are approximately the years in which it is believed that fossil fuels will run out, although the variability of the rate at which they are consumed makes it difficult to say an exact number. Seventy years to look for, explore and define alternatives, since they constitute a very important part of everyday life for the majority of population. Despite the fact that prioritizing policies are promoted, such as using public transport, electric cars… the problem is only postponed but not deleted. Moreover, fossil fuels combustion emit pollutant gases, as carbon dioxide, which in huge quantities contributes to greenhouse effect; nitrogen oxides that contribute to acid rain; and carbon monoxide and hydrocarbons that cause skin and respiratory problems. One alternative to fossil fuels are biofuels. There are some bacteria able to use syngas, a mix of primarily hydrogen, carbon monoxide and carbon dioxide, as a hydrogen and reducing power source for alcohols production. Acetogenic bacteria are obligate anaerobes capable of growing with inorganic carbon as the unique carbon and reducing power source through the Wood-Ljungdahl pathway (WLP). Formate is a metabolite produced in this way, in which an acetil-CoA molecule is transformed into acids and alcohols, at the expense of huge quantities of reducing power. For this reason, formate was presented as an already reduced carbon compound to help in the increase of alcohols production. This work studies the effect of formate addition in acid and alcohol production of two bacterial species, Clostridium ljungdahlii and Clostridium autoethanogenum, during their stationary phase. It has been also studied the genetic expression of a formate transporter during the growing phase, because it is thought that it can work as an efflux pump, regulating formate intracellular level in order to avoid its toxicity. Thus, it has been concluded that formate addition at stationary phase of bacteria does not have any effect on their alcohol production, and also that bacteria presented a rapid consume of formate when it was added at the beginning of the exponential growth phase, but not an enhancement of their productivity