SS2.05 Phylogenetic and Physiologic Successions in Aquatic Bacterial Communities
Date: Monday, June 10, 2002
Time: 2:00:00 PM
Location: Carson C
StepanauskasR, University of Georgia, Athens, USA,
Moran, M, A, University of Georgia, Athens, USA,
Bergamaschi, B, A, U.S. Geological Survey, Sacramento, USA,
Hollibaugh, J, , University of Georgia, Atehns, USA,
Environmental controls of bacterioplankton composition in San Francisco Delta
We examined seasonal and spatial variation in bacterioplankton composition in the San Francisco Delta using terminal restriction fragment length polymorphism (T-RFLP) analysis. Cloned 16S rRNA genes from this system were used to identify taxa represented in the T-RFLP profiles. Principal component analysis of T-RFLP profiles revealed grouping of samples on a seasonal rather than spatial basis. The strongest association with summer/fall communities was demonstrated by Actinomycetes related to Microthrix, beta-Proteobacteria related to Ralstonia, and alfa-Proteobacteria identical to clone LD12. Geobacter-related delta-Proteobacteria and Sanguibacter–related Actinomycetes showed a relative increase during winter/spring, indicating that they were washed out from watershed soils. In an attempt to explain ribotype distribution by environmental controls, a partial least squares regression model was constructed using 14 available X-variables. Four X-variables remained after model optimization: concentration of bioavailable dissolved organic carbon (BDOC), pH, temperature, and river water discharge to the Delta. The highest predictability was achieved for the Ralstonia-, LD12-, and Microthrix- related ribotypes, with corresponding Q^2=0.46, 0.43, and 0.31. These ribotypes were associated with low water discharge and high pH and temperature, indicating that they thrived during summer/autumn conditions with increased primary production and decreased inputs of allochthonous DOC. On the other hand, delta-Proteobacteria and Sanguibacter– related Actinomycetes were associated with high water discharge and low pH and temperature conditions, supporting their terrestrial origin.