Abstract: The invention provides a non-naturally occurring microbial organism having an acetyl-CoA pathway and the capability of utilizing syngas or syngas and methanol. In one embodiment, the invention provides a non-naturally occurring microorganism, comprising one or more exogenous proteins conferring to the microorganism a pathway to convert CO, CO2 and/or H2 to acetyl-coenzyme A (acetyl-CoA), methyl tetrahydrofolate (methyl-THF) or other desired products, wherein the microorganism lacks the ability to convert CO or CO2 and H2 to acetyl-CoA or methyl-THF in the absence of the one or more exogenous proteins. For example, the microbial organism can contain at least one exogenous nucleic acid encoding an enzyme or protein in an acetyl-CoA pathway. The microbial organism is capable of utilizing synthesis gases comprising CO, CO2 and/or H2, alone or in combination with methanol, to produce acetyl-CoA.