Response of a member of the Verrucomicrobia, among the dominating bacteria in a hypolimnion, to increased phosphorus availability

In Lake Siggeforasjon, Sweden, a member of the Verrucomicrobia was found to be a large constituent of the bacteria in the hypolimnion, but not in the epilimnion. In a mesocosm experiment in the epilimnion, this particular Verrucomicrobia was favoured by increased phosphorus availability. The community composition of bacterioplankton was investigated by denaturing gradient gel electrophoresis (DGGE) and sequencing of 16S rDNA.During the last decade, molecular studies of the taxonomic composition of bacterioplankton communities in lakes and oceans have led to the discovery of a large number of ‘new’ bacteria (Giovannoni and Rappe, 2000; Glockner et al., 2000). The occurrence of different bacterial taxa in the plankton community varies in time and space, and thus these taxa are likely to play different roles in the ecosystems. Recent results have indicated that the number of bacterioplankton taxa that still remain to be discovered is limited (Hagstrom et al., 2002; Zwart et al., 2002). However, so far, very little is known about the ecology of individual bacterioplankton species, for instance about which environmental factors can impact their abundance (Zwart et al., 2002).The purpose of this study was to investigate the factors that affect the composition of bacterioplankton at different depths in lakes. We compared the bacterioplankton communities in the epilimnion and the hypolimnion of a lake, and performed a 4 day mesocosm experiment where phosphorus (P) availability was manipulated to test whether it contributed to differences in bacterioplankton community composition between the layers.The community composition of bacterioplankton was investigated by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA, as described previously (Lindstrom, 1998). DGGE is a method that can be used to obtain an overview of the composition of the most dominant bacterioplankton taxa e.g. (Torsvik et al., 1998). The pairwise similarity of the gel patterns of the samples was calculated using Sorensen’s index (Sorensen, 1948).Samples were taken from the temperate dimictic Lake Siggeforasjon, located near Uppsala, in the southern part of central Sweden (59°N, 17°E). This lake is oligo-mesotrophic and moderately humic (Table I). The community composition of the bacterioplankton in the lake has been investigated previously (Lindstrom, 1998, 2000; Lindstrom and Leskinen, 2002).