Figure 1: Examples of interactions between environmental factors. We represent two factors as two different environmental molecules, A and B. These two environmental factorsinteract if these have a non-additive effect on the behavior of microbial cultures. Diverse mechanisms can give rise to interactions, for instance,(a) they can be direct due to physico-chemical modifications, such as through a chemical reaction between them. They may also have an indirect origin, for instance (b) when their combined effect on population attributes is mediated by the genetic or metabolic network of an organism. Their origin may also be ecological (c) mediated by ecological effects between member species of a community, such as when the combination of two different nutrients leads to community compositions that differ from those of the sum of the monocultures.
Given their potential complexity, interactions between environmental axes may substantially complicate the task of identifying culture conditions that will optimize microbial functions, and thus may be seen as a detriment to engineering the environment in a rational manner. Despite this complication, past work in microbial biotechnology has found ways to deal with interactions and has met success at finding environmental manipulations that will move a target function to more desirable values, both in monocultures and in microbial consortia.
In the following, we will overview the current state of these efforts. We will begin by briefly overviewing recent work on disentangling the effect of combinatorial interactions between environmental factors in both monocultures and consortia. We will then overview the current state of the field in exploring combinatorial spaces of environmental factors, in search for environments that optimize the function of monocultures and consortia. We finish with an outlook where we propose potential future directions that may help move the field forward.