This disparity likely resides in the higher complexity of the metabolic routes present
in the mixed culture, where a multiplicity of metabolically active
hydrogenotrophs and hydrogenic microorganisms may coexist.
For example, the acetogenic Wood–Ljungdahl pathway corresponds to a H2 consumption route present in some clostridial strains, where acetate is formed directly by reduction of CO2,
preferentially with H2 as reducing agent [43]. In principle, microbial consortia provide useful combinations of metabolic pathways,
important to a more efficient bioconversion of complex substrates.
However, these mixed cultures must be well controlled since bacterial successions with negative impact on H2 production may
occur [44]. Unexpected process changes, such as in the substrate
composition, may also generate difficulties in controlling the
microbial populations and reproducing the maximum H2 yields.