Covariance of bacterioplankton composition and environmental variables in a temperate delta system
Ramunas Stepanauskas1,3, Mary Ann Moran1, Brian
A. Bergamasch2, James T. Hollibaugh1
1Department of Marine Sciences, University of
Georgia, Athens, Georgia 30602-3636, USA
2US Geological Survey, California State University, Placer
Hall MIS 6129, 6000 J Street. Sacramento, California 95819-6129, USA
3Present address: Savannah River Ecology Laboratory, Drawer
E, Aiken, South Carolina 29802, USA
ABSTRACT: We examined seasonal and spatial variation
in bacterioplankton composition in the Sacramento-San Joaquin River Delta
(CA) using terminal restriction fragment length polymorphism (T-RFLP)
analysis, Cloned 16S rRNA genes from this system were used for putative
identification of taxa dominating the T-RFLP profiles, Both cloning and
T-RFLP analysis indicated that Actinobacteria, Verrucomicrobia, Cytophaga-Flavobacterium
and Proteobacteria were the most abundant bacte- rioplankton
groups in the Delta, Despite the broad variety of sampled habitats (deep
water channels, lakes, marshes, agricultural drains, freshwater and brackish
areas), and the spatial and temporal dif- ferences in hydrology, temperature
and water chemistry among the sampling campaigns, T-RFLP electropherograms
from all samples were similar, indicating that the same bacterioplankton
phylo- types dominated in the various habitats of the Delta throughout
the year. However, principal compo- nent analysis (PCA) and partial least-squares
regression (PLS) of T-RFLP profiles revealed consistent grouping of samples
on a seasonal, but not a spatial, basis.Proteobacteria related to Ralstonia,
Acti- nobacteria related to Microthrix, and I3-Proteobacteria identical
to the environmental Clone LD12 had the highest relative abundance in
summer/fall T-RFLP profiles and were associated with low river flow, high
pH, and a number of optical and chemical characteristics of dissolved
organic carbon (DOC) indicative of an increased proportion of phytoplankton-produced
organic material as opposed to allochthonous, terrestrially derived organic
material. On the other hand, Geobacter-related Proteobacteria showed a
relative increase in abundance in T-RFLP analysis during winter/spring,
and probably were washed out from watershed soils or sediment. Various
phylotypes associated with the same phylogenetic division, based on tentative
identification of T-RFLP fragments, exhibited diverse seasonal patterns,
suggesting that ecological roles of Delta bacterioplankton were partitioned
at the genus or species level.
KEY WORDS: Bacterioplankton biogeography, 16S rRNA, T-RFLP,
Clone libraries, Dissolved organic matter
SREL Reprint #2784
Stepanauskas, R., M. Moran, B. A. Bergamaschi and J. T. Hollibaugh. 2003. Covariance of bacterioplankton composition and environmental variables in a temperate delta system. Aquatic Microbial Ecology 31:85-98.
