Prokaryotic diversity in Aran-Bidgol salt lake, the largest hypersaline playa in Iran

Abstract

Prokaryotic diversity in Aran-Bidgol salt lake, a thalasohaline lake in Iran, was studied by fluorescence in situ hybridization (FISH), cultivation techniques, denaturing gradient gel electrophoresis (DGGE) of PCR-amplified fragments of 16S rRNA genes and 16S rRNA gene clone library analysis. Viable counts obtained (2.5-4 × 10(6) cells mL(-1)) were similar to total cell abundance in the lake determined by DAPI direct count (3-4×10(7) cells mL(-1)). The proportion of Bacteria to Archaea in the community detectable by FISH was unexpectedly high and ranged between 1:3 and 1:2. We analyzed 101 archaeal isolates and found that most belonged to the genera Halorubrum (55%) and Haloarcula (18%). Eleven bacterial isolates obtained in pure culture were affiliated with the genera Salinibacter (18.7%), Salicola (18.7%) and Rhodovibrio (35.3%). Analysis of inserts of 100 clones from the eight 16S rRNA clone libraries constructed revealed 37 OTUs. The majority (63%) of these sequences were not related to any previously identified taxa. Within this sampling effort we most frequently retrieved phylotypes related to Halorhabdus (16% of archaeal sequences obtained) and Salinibacter (36% of bacterial sequences obtained). Other prokaryotic groups that were abundant included representatives of Haloquadratum, the anaerobic genera Halanaerobium and Halocella, purple sulfur bacteria of the genus Halorhodospira and Cyanobacteria.

Fig. 1

Location of the Aran-Bidgol lake and sampling sites (B, G, O, and R) used in this study.

Fig. 2

Phylogenetic reconstruction of 16S rRNA of archaeal sequences recovered from Aran-Bidgol lake. The most likely topology shown here was obtained under the General-Time-Reversible substitution model with gamma distributed rate heterogeneity and a proportion of invariable sites (GTR + Γ + I). Scale represents the expected number of substitutions per site. Significantly supported nodes are marked with bullets.

Fig. 3

Phylogenetic reconstruction of 16S rRNA of bacterial sequences recovered from Aran-Bidgol lake. The most likely topology shown here was obtained under the General-Time-Reversible substitution model with gamma distributed rate heterogeneity and a proportion of invariable sites (GTR + Γ + I). Scale represents the expected number of substitutions per site. Significantly supported nodes are marked with bullets.

Fig. 4

Phylotype diversity for Archaea and Bacteria in Aran-Bidgol lake. The bar chart compares 16S rRNA sequence diversities of phylotypes recovered from four sampling sites (sites B, G, O, and R) at the lake. Abbreviations: Bacteria: Sal: Salinibacter; Bac: other Bacteroidetes; Hcl: Halocella; Dsf: Desulfovermiculus; Cyn: Cyanobacteria; Hrs: Halorhodospira, Hal: Halanaerobium. Archaea: Eur: Euryarchaea other than Halobacteriales; Hnt: Halonotius, Hrb: Halorhabdus; Har: Haloarcula; Nat: Natronomonas, Hrr: Halorubrum; Haq: Haloquadratum; Hbc: Halobacterium, OS: Other sequences not affiliated with identified taxa.

Fig. 5

DGGE analysis of archaeal (left) and bacterial (right) diversity in Aran-Bidgol. Samples from four sampling sites (B, G, O, and R) indicated in separate column.

Fig. 6

Rarefaction curve of obtained archaeal (filled circle) and bacterial (empty circle) sequences determined at a distance of 3% as implemented in MOTHUR (32) using 16S rRNA gene clone library sequences from Aran-Bidgol lake.