Comparative community genomics in the Dead Sea: an increasingly extreme environment

Abstract

Owing to the extreme salinity (B10 times saltier than the oceans), near toxic magnesium levels (B2.0 M Mg 2 þ ), the dominance of divalent cations, acidic pH (6.0) and high-absorbed radiation flux rates, the Dead Sea represents a unique and harsh ecosystem. Measures of microbial presence (microscopy, pigments and lipids) indicate that during rare bloom events after exceptionally rainy seasons, the microbial communities can reach high densities. However, most of the time, when the Dead Sea level is declining and halite is precipitating from the water column, it is difficult to reliably measure the presence of microorganisms and their activities. Although a number of halophilic Archaea have been previously isolated from the Dead Sea, polar lipid analyses of biomass collected during Dead Sea blooms suggested that these isolates were not the major components of the microbial community of these blooms. In this study, in an effort to characterize the perennial microbial community of the Dead Sea and compare it with bloom assemblages, we performed metagenomic analyses of concentrated biomass from hundreds of liters of brine and of microbial material from the last massive Dead Sea bloom. The difference between the two conditions was reflected in community composition and diversity, in which the bloom was different and less diverse from the residual brine population. The distributional patterns of microbial genes suggested Dead Sea community trends in mono-and divalent cation metabolisms as well as in transposable elements. This may indicate possible mechanisms and pathways enabling these microbes to survive in such a harsh environment.

Geographical Location Determines the Population Structure in Phyllosphere Microbial Communities of a Salt-Excreting Desert Tree

“…The same analysis, performed using other weighted distance measures such as Morisita-Horn (12) and an unweighted one (6), yielded very similar results (data not shown). Two related non-Tamarix samples were added to the analysis: a sample from the gut of a T. nilotica phyllosphere insect, Oxyrrachis versicolor, collected from a tree in an oasis by the Dead Sea (O. M. Finkel et al, unpublished data), and a sample taken from Dead Sea water during a 1992 algal bloom (5). To evaluate the taxonomic depth of differences and similarities between samples, these analyses were performed at three levels: order, family, and genus.…”

Virioplankton Community Structure in Tunisian Solar Salterns

“…The 4 metaviromes reported in the present work were complemented with a selection of 24 additional metagenomes found in the literature, and all possible pairwise BLASTn comparisons were carried out. Additional data sets comprised metagenomes from C4Oct, M1Oct, TSOct, and TSMay (present work); 19 high-, medium-, and low-salinity metagenomes from San Diego (26); 3 metagenomes from Santa Pola's CR30 crystallizer pond (28, 32, 51); 1 metagenome from Lake Retba (53); and 1 metagenome from the Dead Sea (18). The BLASTn results were automatically parsed to calculate the amount of nonredundant nucleotides from an Sfax metavirome "A" that were shared with a second selected metagenome "B" by means of meaningful BLAST high-scoring segment pairs (HSPs) (i.e., a maximum E-value of 0.001, a minimum of 80% sequence identity, and a minimum alignment length of 100 positions).…”

Seasonal fluctuations in ionic concentrations drive microbial succession in a hypersaline lake community

“…Achieving this goal requires coordinated, detailed, accurate measurements of both physical and biological factors, but obtaining this information over temporal and spatial scales relevant to natural microbial communities is challenging. Extreme hypersaline aqueous environments harboring limited phylogenetic diversity provide tractable model ecosystems to confront these challenges (Demergasso et al, 2008;Bodaker et al, 2009;Pagaling et al, 2009;Oh et al, 2010;Boujelben et al, 2012;MakhdoumiKakhki et al, 2012;Oren, 2013). Although overall salt concentrations in these habitats are, by definition, at or exceeding the limits of ionic solubility, geochemical variation in water sources as well as minerals dissolved from surrounding rocks and sediments contribute to variable ratios of different ionic species over space and time (Javor, 1989;Oren, 2013).…”