Abstract
Multi-species microbial communities often display functions - biochemical activities unattainable by member species alone, such as fighting pathogens or degrading wastes. Artificially selecting high community function is useful but rarely attempted. Here, we theoretically examine artificial selection of Helper-Manufacturer communities. Helpers digest Waste and generate Byproduct essential to Manufacturers; Manufacturers divert a fraction of their growth to make Product. Thus, community function - total Product accumulated as a low-density “Newborn” community grows over “maturation time” T into an “Adult” community - is costly to Manufacturers. Despite pre-optimizing Helper and Manufacturer monocultures, community function is sub-optimal. To improve community function, we simulate community selection by allowing cells in Newborn communities to grow and mutate, and select highest-functioning Adults to “reproduce” by diluting each into multiple Newborns. We find that fluctuations in Newborn composition during community reproduction (e.g. due to pipetting) can interfere with selection, and reducing fluctuations (e.g. via cell sorting) facilitates selection.
