Distribution and diversity of archaea corresponding to the limnological cycle of a hypersaline stratified lake (Solar lake, Sinai, Egypt)

Abstract

The vertical and seasonal distribution and diversity of archaeal sequences was investigated in a hypersaline, stratified, monomictic lake, Solar Lake, Sinai, Egypt, during the limnological development of stratification and mixing. Archaeal sequences were studied via phylogenetic analysis of 16S rDNA sequences as well as denaturing gradient gel electrophoresis analysis. The 165 clones studied were grouped into four phylogenetically different clusters. Most of the clones isolated from both the aerobic epilimnion and the sulfide-rich hypolimnion were defined as cluster I, belonging to the Halobacteriaceae family. The three additional clusters were all isolated from the anaerobic hypolimnion. Cluster II is phylogenetically located between the genera Methanobacterium and Methanococcus. Clusters III and IV relate to two previously documented groups of uncultured euryarchaeota, remotely related to the genus Thermoplasma. No crenarchaeota were found in the water column of the Solar Lake. The archaeal community in the Solar Lake under both stratified and mixed conditions was dominated by halobacteria in salinities higher than 10%. During stratification, additional clusters, some of which may possibly relate to uncultured halophilic methanogens, were found in the sulfide- and methane-rich hypolimnion.

FIG. 1

Limnological conditions of Solar Lake during holomixis (September [Sept.] 1997), early stratification (December [Dec.] 1997), and late stratification (June 1997). Symbols: ■, temperature; ▴, salinity; ●, oxygen; ○, sulfide; ▄, methane. Note different x axis values for the three methane profiles.

FIG. 2

Phylogenetic tree of Archaea sequences detected in Solar Lake. The bar indicates a 10% estimated difference in nucleotide sequences.

FIG. 3

DGGE profiles showing sequence types from selected samples during holomixis, early stratification, and late stratification of Solar Lake. (Upper gel) DGGE of selected environmental samples from holomixis and early stratification compared to those of selected cones in order to identify known bands according to their relative levels of migration. Bands A1 to A7 are represented by the white lines seen on both sides of the gel. (Lower gel) DGGE of selected environment samples from late stratification compared to excised bands from the gel, which were sequenced and rerun to confirm sequence pattern. Sept., September; Dec., December.