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Temporal changes in species interactions in simple aquatic bacterial communities.

Pekkonen M, Laakso JT - BMC Ecol. (2012)

Bottom Line: Changes in the resource environment caused complex time and species composition-dependent effects on bacterial growth performance.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Integrative Ecology Unit, Department of Biosciences, P,O, Box 65, FIN-00014 University of Helsinki, Helsinki, Finland. minna.pekkonen@helsinki.fi

ABSTRACT

Background: Organisms 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.

Results: Changes 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.

Conclusions: The 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.

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Growth rates in filtrates. Maximum instantaneous growth rates (r ± s.e.m.) of A) S. marcescens and B) N. capsulatum in filter-sterilized medium. The first species in the legend indicates the consumer species and the second the test species. Consumer species grew in the medium before filtering, and test species’ growth rate was measured in the filtered medium. X-axis is the resource consumption time before filtering, at t = 0 h is the growth rate in unconsumed medium.
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Figure 3: Growth rates in filtrates. Maximum instantaneous growth rates (r ± s.e.m.) of A) S. marcescens and B) N. capsulatum in filter-sterilized medium. The first species in the legend indicates the consumer species and the second the test species. Consumer species grew in the medium before filtering, and test species’ growth rate was measured in the filtered medium. X-axis is the resource consumption time before filtering, at t = 0 h is the growth rate in unconsumed medium.

Mentions: Novosphingobium capsulatum grew faster than Serratia marcescens in unconsumed medium (r ± s.e.m. 0.239 ± 0.004 and 0.155 ± 0.005, respectively; t = -12.89, df = 18, p < 0.001, compare Figure3A and Figure3B, at t = 0 h). The growth rates of S. marcescens and N. capsulatum in consumed medium differed between species and also changed in time (Test sp., Time effect, and their interaction, see Table1). Moreover, the consumer identity producing the filtrate affected the growth dynamics (Consumer sp., Table1). Based on the F-values the test species identity had the strongest effect on growth rates (between subjects effects, Table1).


Temporal changes in species interactions in simple aquatic bacterial communities.

Pekkonen M, Laakso JT - BMC Ecol. (2012)

Growth rates in filtrates. Maximum instantaneous growth rates (r ± s.e.m.) of A) S. marcescens and B) N. capsulatum in filter-sterilized medium. The first species in the legend indicates the consumer species and the second the test species. Consumer species grew in the medium before filtering, and test species’ growth rate was measured in the filtered medium. X-axis is the resource consumption time before filtering, at t = 0 h is the growth rate in unconsumed medium.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3526521&req=5

Figure 3: Growth rates in filtrates. Maximum instantaneous growth rates (r ± s.e.m.) of A) S. marcescens and B) N. capsulatum in filter-sterilized medium. The first species in the legend indicates the consumer species and the second the test species. Consumer species grew in the medium before filtering, and test species’ growth rate was measured in the filtered medium. X-axis is the resource consumption time before filtering, at t = 0 h is the growth rate in unconsumed medium.
Mentions: Novosphingobium capsulatum grew faster than Serratia marcescens in unconsumed medium (r ± s.e.m. 0.239 ± 0.004 and 0.155 ± 0.005, respectively; t = -12.89, df = 18, p < 0.001, compare Figure3A and Figure3B, at t = 0 h). The growth rates of S. marcescens and N. capsulatum in consumed medium differed between species and also changed in time (Test sp., Time effect, and their interaction, see Table1). Moreover, the consumer identity producing the filtrate affected the growth dynamics (Consumer sp., Table1). Based on the F-values the test species identity had the strongest effect on growth rates (between subjects effects, Table1).

Bottom Line: Changes in the resource environment caused complex time and species composition-dependent effects on bacterial growth performance.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Integrative Ecology Unit, Department of Biosciences, P,O, Box 65, FIN-00014 University of Helsinki, Helsinki, Finland. minna.pekkonen@helsinki.fi

ABSTRACT

Background: Organisms 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.

Results: Changes 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.

Conclusions: The 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.

Show MeSH