Temporal changes in species interactions in simple aquatic bacterial communities

Abstract

BackgroundOrganisms modify their environment and in doing so change the quantity and possibly the quality of available resources. Due to the two-way relationship between organisms and their resource environment, and the complexity it brings to biological communities, measuring species interactions reliably in any biological system is a challenging task. As the resource environment changes, the intensity and even the sign of interactions may vary in time. We used Serratia marcescens and Novosphingobium capsulatum bacteria to study how the interaction between resource environment and organisms influence the growth of the bacterial species during circa 200 generations. We used a sterile-filtering method to measure how changes in resource environment are reflected in growth rates of the two species.ResultsChanges in the resource environment caused complex time and species composition-dependent effects on bacterial growth performance. Variation in the quality of the growth medium indicated existence of temporally fluctuating within-species facilitation and inhibition, and between-species asymmetric facilitation.ConclusionsThe interactions between the community members could not be fully predicted based only on the knowledge of the growth performance of each member in isolation. Growth dynamics in sterile-filtered samples of the conditioned growth medium can reveal both biologically meaningful changes in resource availability and temporally changing facilitative resource-mediated interactions between study species. This is the first study we are aware of where the filter-sterilization – growth assay method is applied to study the effect of long-term changes in the environment on species interactions.

Resource Availability and Competition Shape the Evolution of Survival and Growth Ability in a Bacterial Community

“…According to our earlier study, a cross-feeding interaction is possible between S. marcescens and N. capsulatum . When the growth rate of each species was tested in a sterile-filtered medium where the other species had consumed the resources for 1 to 168 h, the growth rates in consumed medium were occasionally faster than in unconsumed medium [27]. Serratia marcescens had a relatively high growth rate in medium consumed by N. capsulatum for 1 to 10 h, whereas N. capsulatum had high growth rates in medium consumed by S. marcescens for 30 to 50 h [27].…”

“…When the growth rate of each species was tested in a sterile-filtered medium where the other species had consumed the resources for 1 to 168 h, the growth rates in consumed medium were occasionally faster than in unconsumed medium [27]. Serratia marcescens had a relatively high growth rate in medium consumed by N. capsulatum for 1 to 10 h, whereas N. capsulatum had high growth rates in medium consumed by S. marcescens for 30 to 50 h [27]. However, results presented here show that when these species grew together for prolonged time, they did not evolve to be dependent on a cross-feeding interaction.…”

“…Alternatively, it could be speculated that the qualitative changes in the growth environment due to bacterial metabolism and resource consumption may also influence biofilm production [59–62]. We know that during one week the quality of the resource environment changes and affects bacterial growth rates [27]. However, the effect of changing resource conditions on biofilm production is not a likely explanation here, as there was no consistent difference in biofilm formation between clones from small and large resource pulse environments.…”

“…The replicated (n=3) experiment lasted 13 weeks enabling the occurrence of evolutionary changes in life history traits. The two bacterial species were chosen on a basis that they differ in their growth strategies, but are able to exploit same resources [26,27]. Serratia marcescens grows quickly when resources are abundant, but on low resource levels growth rate is slow.…”

Evolution of bacterial life-history traits is sensitive to community structure

“…; Lawrence et al. ; Pekkonen and Laakso ). For example, three out of the four species in Lawrence et al.’s study were found to evolve adaptations for avoiding competition, when they evolved in polyculture (Lawrence et al.…”