טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBodaker Idan
Subject"Fishing in the Dead Sea": Environmental Microbial
Genomics and Ecological Diversity of the Dead Sea
Inhabitants
DepartmentDepartment of Biology
Supervisor Professor Oded Beja
Full Thesis textFull thesis text - English Version


Abstract

Due to the extreme salinity (~ 10 times saltier than the oceans), near toxic magnesium levels (~2.0 M Mg2), 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 following 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 an effort to characterize the perennial microbial community of the Dead Sea and compare it to 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, where 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. We reported a haloarchaeon related to Halobacterium salinarum to dominate in a microbial bloom that developed in 1992 in the upper water layers of the lake following massive freshwater runoff. Whether this clade also dominated an earlier bloom in 1980-1982 cannot be ascertained as no samples for cultivation-independent analysis were preserved.

The presence of the light-driven proton pump bacteriorhodopsin was reported in the 1980-1982 bloom of prokaryotes that had developed in the Dead Sea. To test the hypothesis that bacteriorhodopsin proton pumping may play a major role in determining what type of haloarchaea may dominate in specific bloom conditions, we compared rhodopsin genes recovered from Dead Sea biomass collected in different periods with genes coding for retinal proteins in isolated haloarchaea.  Novel bacteriorhodopsin and sensory rhodopsin genes were found in samples collected in 2007 and 2010.