Understanding and harnessing the complexity of interspecies interactions in acetogenic mixotrophic co-cultures

The core advantage of acetogens lies in their superior carbon management, achieved by engaging the Wood-Ljungdahl pathway to sequester CO₂ in situ and utilize exogenous CO₂. This advantage can be further exploited by coupling acetogens with other organisms in co-culture, leading to the increasingly explored concept of acetogenic co-cultures. We review and dissect schemes involving the co-fermentation of carbohydrates and exogenous gases, which present unique challenges and opportunities due to the nonlinearity of co-culture metabolic networks and complex, often unanticipated, interspecies interactions. The latter suggests that most, if not all, such co-cultures are mutualistic rather than commensalistic, contrary to previous assumptions. We discuss both fundamental and applied concepts, including co-culture stability and methods for quantitatively capturing population dynamics and interspecies interactions.