Pseudomonas aeruginosa is an opportunistic pathogen of particular concern to immune-compromised people, such as cystic fibrosis patients and burn victims. These bacteria grow in built environments including hospitals and households, and in natural environments such as rivers and estuaries. However, there is conflicting evidence whether recent environments like the human lung and open ocean affect P. aeruginosa growth performance in alternate environments. We hypothesized that bacteria recently isolated from dissimilar habitats should grow differently in media containing artificial versus natural resources. To test this idea, we examined growth of P. aeruginosa isolates from three environments (estuary, household, and clinic) in three media types: minimal-glucose lab medium, and media prepared from sugar maple leaves or big bluestem grass. We used automated spectrophotometry to measure high-resolution growth curves for all isolate by media combinations, and studied two fitness parameters: growth rate and maximum population density. Results showed high variability in growth rate among isolates, both overall and in its dependence on assay media, but this variability was not associated with habitat of isolation. In contrast, total growth (change in absorbance over the experiment) differed overall among habitats of isolation, and there were media-specific differences in mean total growth among habitats of isolation, and in among-habitat variability in the media-specific response. This was driven primarily by greater total growth of estuary isolates when compared with those from other habitats of origin, and greater media-specific variability among household isolates than those from other habitats of origin. Taken together, these results suggest that for growth rate P. aeruginosa bacteria appear to be broad generalists without regard to current or recent habitat, whereas for total growth a signature of recent ecological history can be detected.
_________________________________________Resources influence the distribution, behavior, growth and reproduction of bacterial species. Understanding how closely related species utilize resources will shed light on the ecological traits or principles that shape biogeographic patterns and promote coexistence of species. Twelve Pseudomonas strains isolated from a single human home and PA01, the standard laboratory strain were evaluated in Luria Bertani media to understand whether their growth traits are influenced by their species group and/or their environment of isolation. Total growth, growth rate, early cumulative area under the growth curve (CUC) over 48 hours and viability (viable bacteria count per ml) at 24 and 48 hours were evaluated for each strain. I found differences in growth strategies that may be driven by species group and/or environment of isolation. These results suggest local adaptation of Pseudomonas strains to human home environments.These strains were also evaluated for their metabolic and oxidative profiles in 31 resources as a way to understand if metabolic and/or oxidative profiles could be predicted by their species group and/or their environment of isolation. Metabolic vi profile for each strain was evaluated as the qualitative ability to use a resource coded as 0 or 1, while the oxidative profile in each resource is a quantitative measure that was determined by integrating the CUC for each resource after 48 hours of growth. I found some resources were utilized by all the strains, suggesting similar metabolic adaptations or common ancestry. I also found evidence for resource differentiation that was driven by species group, but very little evidence for environment of isolation or local adaptation.Thus, resource differentiation can reduce competition and promote coexistence of species.
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