In alternative embodiments, provided are genetically or recombinantly engineered nitrogen-fixing, nitrogenase expressing bacteria capable of enzymatically synthesizing hydrocarbons, and methods for making and using them. In alternative embodiments, provided are genetically or recombinantly engineered nitrogen-fixing, nitrogenase expressing bacteria including nitrogen-fixing diazotrophs such as nitrogen-fixing bacteria of the family Pseudomonadaceae , or the genus Azotobacter , for the whole cell synthesis of hydrocarbons and carbon-carbon bonds. In alternative embodiments, nitrogen-fixing, nitrogenase-expressing bacteria used to practice the invention are genetically or recombinantly engineered to express an exogenous nitrogenase express more endogenous nitrogenase or have increased nitrogenase, activity. In alternative embodiments, nitrogen-fixing, nitrogenase-expressing bacteria used to practice the invention are genetically or recombinantly engineered to lack or have decreased molybdenum transporter activity. In alternative embodiments, provided are culture systems, fermenters and bioreactors using nitrogen-fixing, nitrogenase-expressing bacteria for enzymatically synthesizing hydrocarbons.