High Genetic Diversity and Novelty in Eukaryotic Plankton Assemblages Inhabiting Saline Lakes in the Qaidam Basin

<div><p>Saline lakes are intriguing ecosystems harboring extremely productive microbial communities in spite of their extreme environmental conditions. We performed a comprehensive analysis of the genetic diversity (18S rRNA gene) of the planktonic microbial eukaryotes (nano- and picoeukaryotes) in six different inland saline lakes located in the Qaidam Basin. The novelty level are high, with about 11.23% of the whole dataset showing <90% identity to any previously reported sequence in GenBank. At least 4 operational taxonomic units (OTUs) in mesosaline lakes, while up to eighteen OTUs in hypersaline lakes show very low CCM and CEM scores, indicating that these sequences are highly distantly related to any existing sequence. Most of the 18S rRNA gene sequence reads obtained in investigated mesosaline lakes is closely related to Holozoa group (48.13%), whereas Stramenopiles (26.65%) and Alveolates (10.84%) are the next most common groups. Hypersaline lakes in the Qaidam Basin are also dominated by Holozoa group, accounting for 26.65% of the total number of sequence reads. Notably, Chlorophyta group are only found in high abundance in Lake Gasikule (28.00%), whereas less represented in other hypersaline lakes such as Gahai (0.50%) and Xiaochaidan (1.15%). Further analysis show that the compositions of planktonic eukaryotic assemblages are also most variable between different sampling sites in the same lake. Out of the parameters, four show significant correlation to this CCA: altitude, calcium, sodium and potassium concentrations. Overall, this study shows important gaps in the current knowledge about planktonic microbial eukaryotes inhabiting Qaidam Basin (hyper) saline water bodies. The identified diversity and novelty patterns among eukaryotic plankton assemblages in saline lake are of great importance for understanding and interpreting their ecology and evolution.</p></div

Locations of investigated lakes in Qaidam Basin.

<p>In Figure, K, T, D, M, X and G referred to Lake Keluke, Lake Tuosu, Lake Dasugan, Lake Gahai, Lake Xiaochaidan and Lake Gsikule, respectively.</p

CCA biplots based on OTU and geographical or selected chemical parameters.

<p>Chemical parameters yield in a very similar spreading of sampling sites; DO dissolved oxygen, TN total nitrogen, TDS total dissolved solid. K, Na, Ca, Cl, SO4 was represent for ions potassium (K⁺), sodium (Na⁺), calcium (Ca²⁺), chloride (Cl⁻), and sulfate (SO₄²⁻), respectively. In Figure, K, T, D, M, X and G referred to Lake Keluke, Lake Tuosu, Lake Dasugan, Lake Gahai, Lake Xiaochaidan and Lake Gsikule, respectively.</p

The geographical, physical, and chemical characteristics of the investigated lakes. <i>ND</i> not determined, <i>n.d</i>. not detectable.

<p>The geographical, physical, and chemical characteristics of the investigated lakes. <i>ND</i> not determined, <i>n.d</i>. not detectable.</p

Taxa assignments at Class rank or below of investigated sample sits and the most abundant taxa in each habitat.

<p>(A) Taxa assignments at Class rank or below of investigated sample sits. (B) Taxa assignments at Class rank or below in each habitat. The class “other” means group that could not be precisely assigned to any known eukaryotic taxonomic group. The class “norank” means group that could not be precisely assigned to eukaryotic taxonomic group at least at the class level within kingdom. “Incertae sedis” is a term used for a taxonomic group where its broader relationships are unknown or undefined.</p

Novelty pattern plot for the different eukaryal classes found in mesosaline lake and hypersaline lake.

<p>(A) mesosaline saline, (B) hypersaline. Closest environmental match (CEM) and the closest cultured match (CCM) available in GenBank (BLAST search, May 2014). Dots below 61% similarity in both axes indicated no similarity sequences.</p

PCA analyses on DO, pH, TN and ion percentages of investigated Tibetan lakes.

<p>DO dissolved oxygen, TN total nitrogen, TDS total dissolved solid. K, Na, Ca, Mg, Cl, SO4 was represent for ions potassium (K⁺), sodium (Na⁺), calcium (Ca²⁺), magnesium(Mg²⁺), chloride (Cl⁻), and sulfate (SO₄²⁻), respectively. The numbers 1 to 13 refer to investigated lakes, Lake Keluke (G1, G3), Lake Gahai (M1, M7), Lake Dasugan (D10, D11), Lake Tuosu (T3, T11, T12), and Lake Keluke (K11, K13), respectively.</p

Statistics of Taxonomic Composition of investigated lakes.

<p>Statistics of Taxonomic Composition of investigated lakes.</p

ML phylogenetic tree with 18S rDNA sequences of eukaryotes retrieved from the investigated lakes in the Qaidam Basin.

<p>The tree was constructed using 733 sequences. (A) Tree ignoring branch lengths and overlaid with colors with independent taxonomic assignations of sequences to an eukaryotic supergroup. The branches with cyan colors correspond to unclassified eukaryotes. (B) Same tree showing branch lengths, colored as before. The scale bar indicates 0.1 substitutions per position.</p