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. The invention additionally provides a method for producing acetyl-CoA, for example, by culturing an acetyl-CoA producing microbial organism, where the microbial organism expresses at least one exogenous nucleic acid encoding an acetyl-CoA pathway enzyme or protein in a sufficient amount to produce acetyl-CoA, under conditions and for a sufficient period of time to produce acetyl-CoA.