NOVELTY - An isolated microbial consortia (C1) comprises a first-bite microbial consortium that converts a starting hydrocarbon containing a complex hydrocarbon into at least two first-bite metabolic products; and a downstream microbial consortium that converts a starting hydrocarbon metabolic product into a downstream metabolic product, where the downstream metabolic product has a greater mol. % hydrogen than the starting hydrocarbon. The first-bite microbial consortium or downstream microbial consortium comprises species of Desulfuromonas, Fusibacter or Acetobacterium.    USE - For biogenic methane production (claimed).    ADVANTAGE - The isolated microbial consortia provide biogenic enhancement of the mole percentage of hydrogen in hydrocarbon molecules and enhancements in biogenic hydrogen and methane production in geologic formations. The isolated microbial consortia are capable of transforming carbonaceous materials in the formations into molecular hydrogen, and/or hydrocarbons having a larger mole percentage of hydrogen than the starting materials. The isolated microbial consortia contain microorganisms that do not require molecular oxygen as a terminal electron acceptor in their combined metabolism, but rather can perform methanogenesis as the final electron accepting step to produce methane.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: 1) an isolated microbial consortia (C2) for biogenic methane production, comprising a first microbial consortium that converts a starting hydrocarbon into intermediate compounds; a second microbial consortium that converts at least one type of the intermediate compounds into CO2 and H2; and a third microbial consortium that converts the CO2 and H2 into methane and water, where at least one of the first, second and third microbial consortiums comprises at least one species of Desulfuromonas; 2) an isolated microbial consortia (C3) for biogenic methane production comprising a first microbial consortium that converts a starting hydrocarbon into intermediate compounds; a second microbial consortium that converts at least one type of the intermediate compounds into acetate; and a third microbial consortium that converts the acetate into methane and water, where at least one of the first, second and third microbial consortiums comprises at least one species of Desulfuromonas.