Conclusions
Microbial activity of oil wells has a significant impact on oil recovery efficiencies, the souring of produced oil or H2S generation, and final oil composition. Top-down engineering approaches via direct nutrient injection and supplementation can be used to shape community structure and control metabolism. We validated the ability of molasses supplemented with nitrate and/or molybdate to apply different selective pressures which were either competitive or inhibitory of H2S production, respectively. Molybdate supplementation in particular provided strong selective pressure whose effects persisted over multiple generations or passages once removed, demonstrating a strong capacity to shape community composition and function. While these did not enhance oil recovery in our coreflood experiments under the conditions tested, top-down engineering had demonstrable impact on the composition of oil recovered and inhibiting microbial souring processes. Our work highlights the power of microbiome engineering for the improvement of oil recovery operations and develops a workflow for the rapid screening and evaluation of candidate oil wells.