Consumer-resource dynamics are altered by interspecies signaling

How do assemblages of bacteria in microbial communities maintain their diversity? Consumer-resource models explain the maintenance of diversity by mapping the availability of resources to a growth rate for each bacterial species. A key assumption of these models is that the growth rate is directly mappable to resource consumption rates. To test this assumption experimentally, we measured the growth rates of Acetobacter and Lactobacillus species isolated from the Drosophila gut. We found that the growth rates of the bacterial strains grown in co-culture are different from their growth rates in monoculture due to physiolgical changes, not as a result of differences in nutrients, but due to interspecies signaling that triggers transciptional changes. One of these transcriptional responses is the upregulation of nutrient transporters under certain co-culture conditions, which allows the bacteria to use specific nutrients at higher rates, enabling faster growth. Modification of a consumer resource model to account for these conditional nutrient utilization rates improves the data fit albeit at a cost of higher model complexity. Our results highlight an important and often overlooked parameter in microbial community dynamics.