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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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Biomass and population size during one week. A) Biomass dynamics as optical density (OD), and B) population size as colony forming units (CFUml-1) during one week’s growth, when Serratia marcescens and Novosphingobium capsulatum where grown either separately or together in batch cultures. For the two-species community, the biomass is combined for both species.
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Figure 1: Biomass and population size during one week. A) Biomass dynamics as optical density (OD), and B) population size as colony forming units (CFUml-1) during one week’s growth, when Serratia marcescens and Novosphingobium capsulatum where grown either separately or together in batch cultures. For the two-species community, the biomass is combined for both species.

Mentions: All populations grew approximately following the logistic growth (Figure1). Based on the colony forming units (CFUml-1) data the time lag before exponential growth phase was circa 5 h for S. marcescens, and 10 h for N. capsulatum (Figure1B). After 70 h of growth the total biomass (measured as optical density) reached its peak and was highest in the two-species community (Figure1A). It was not possible to separate species-specific biomasses in the two-species communities, but when grown separately N. capsulatum produced more biomass than S. marcescens (Figure1A). However, based on the CFUs S. marcescens had higher population sizes than N. capsulatum in isolation (Figure1B). When S. marcescens grew alone the number of CFUml-1 declined during the first five hours of growth (Figure1B). After an initial time lag in growth S. marcescens was 10–60 times more abundant in two-species communities than N. capsulatum (Figure2). At the end of the week’s growth the population size of S. marcescens was 108 CFUml-1 and N. capsulatum was 107 CFUml-1 both in isolation and in two species communities.


Temporal changes in species interactions in simple aquatic bacterial communities.

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

Biomass and population size during one week. A) Biomass dynamics as optical density (OD), and B) population size as colony forming units (CFUml-1) during one week’s growth, when Serratia marcescens and Novosphingobium capsulatum where grown either separately or together in batch cultures. For the two-species community, the biomass is combined for both species.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Biomass and population size during one week. A) Biomass dynamics as optical density (OD), and B) population size as colony forming units (CFUml-1) during one week’s growth, when Serratia marcescens and Novosphingobium capsulatum where grown either separately or together in batch cultures. For the two-species community, the biomass is combined for both species.
Mentions: All populations grew approximately following the logistic growth (Figure1). Based on the colony forming units (CFUml-1) data the time lag before exponential growth phase was circa 5 h for S. marcescens, and 10 h for N. capsulatum (Figure1B). After 70 h of growth the total biomass (measured as optical density) reached its peak and was highest in the two-species community (Figure1A). It was not possible to separate species-specific biomasses in the two-species communities, but when grown separately N. capsulatum produced more biomass than S. marcescens (Figure1A). However, based on the CFUs S. marcescens had higher population sizes than N. capsulatum in isolation (Figure1B). When S. marcescens grew alone the number of CFUml-1 declined during the first five hours of growth (Figure1B). After an initial time lag in growth S. marcescens was 10–60 times more abundant in two-species communities than N. capsulatum (Figure2). At the end of the week’s growth the population size of S. marcescens was 108 CFUml-1 and N. capsulatum was 107 CFUml-1 both in isolation and in two species communities.

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