The community of organisms inhabiting the water-filled leaves of the carnivorous pitcher plant Sarracenia purpurea includes arthropods, protozoa and bacteria, and serves as a model system for studies of food web dynamics. Despite the wealth of data collected by ecologists and zoologists on this food web, very little is known about the bacterial assemblage in this microecosystem.

We sought to characterize and understand the forces controlling the structure of the bacterial assemblages occurring within pitchers. We used T-RFLP analysis to quantify bacterial diversity within the pitchers as a function of pitcher size, pH of the pitcher fluid and the presence of the keystone predator in this food web, larvae of the pitcher-plant mosquito Wyeomyia smithii. Results were analyzed at two spatial scales: within a single bog and across three isolated bogs to characterize patterns of biogeography in the bacterial assemblage.Results/Conclusions

Our results suggest that the pitchers of S. purpurea were sterile before they opened and the bacterial community of each pitcher is established de novo as pitchers develop.

Composition of the bacterial assemblage was more variable between different bogs than within bogs, even though many of the fragments resulting from the T-RFLP analyses were singletons. Overall, the bacterial richness of the individual pitchers was determined by both the presence of a keystone predator and by the size of the pitcher.

Our results suggest that fundamental ecological concepts derived from macroscopic food webs can also be used to predict the bacterial assemblages in pitcher plants.