Survival dynamics of cystic fibrosis-related Gram-negative bacterial pathogens (Pseudomonas aeruginosa and Burkholderia cenocepacia) in Dead Sea and Atlantic Ocean waters.

Clinical cystic fibrosis (CF) Pseudomonas aeruginosa (n=6) and Burkholderia cenocepacia (n=4) were inoculated in marine brines from the Dead Sea and the Atlantic Ocean and their survival was monitored over a 1 month duration. In Dead Sea samples, all P. aeruginosa and B. cenocepacia isolates were non-detectable by culture following 24 h incubation, including the non-selective enrichment samples. In the Atlantic Ocean brine, over a 1 month period, mean P. aeruginosa counts decreased by only 0.25 log10 units and mean B. cenocepacia counts decreased by approximately 4 log10 units (10,000 cfu/ml). This study demonstrated that Dead Sea brine exerted a lethal effect within 24 h on planktonic P. aeruginosa and B. cenocepacia. Thus, the Dead Sea effectively purges these organisms from its environment on a daily basis.

Genomic adaptations of the halophilic Dead Sea filamentous fungus Eurotium rubrum.

The Dead Sea is one of the most hypersaline habitats on Earth. The fungus Eurotium rubrum (Eurotiomycetes) is among the few species able to survive there. Here we highlight its adaptive strategies, based on genome analysis and transcriptome profiling. The 26.2 Mb genome of E. rubrum shows, for example, gains in gene families related to stress response and losses with regard to transport processes. Transcriptome analyses under different salt growth conditions revealed, among other things differentially expressed genes encoding ion and metabolite transporters. Our findings suggest that long-term adaptation to salinity requires cellular and metabolic responses that differ from short-term osmotic stress signalling. The transcriptional response indicates that halophilic E. rubrum actively counteracts the salinity stress. Many of its genes encode for proteins with a significantly higher proportion of acidic amino acid residues. This trait is characteristic of the halophilic prokaryotes as well, supporting the theory of convergent evolution under extreme hypersaline stress.

Evolution of genomic diversity and sex at extreme environments: fungal life under hypersaline Dead Sea stress.

We have found that genomic diversity is generally positively correlated with abiotic and biotic stress levels (1-3). However, beyond a high-threshold level of stress, the diversity declines to a few adapted genotypes. The Dead Sea is the harshest planetary hypersaline environment (340 g.liter-1 total dissolved salts, approximately 10 times sea water). Hence, the Dead Sea is an excellent natural laboratory for testing the "rise and fall" pattern of genetic diversity with stress proposed in this article. Here, we examined genomic diversity of the ascomycete fungus Aspergillus versicolor from saline, nonsaline, and hypersaline Dead Sea environments. We screened the coding and noncoding genomes of A. versicolor isolates by using >600 AFLP (amplified fragment length polymorphism) markers (equal to loci). Genomic diversity was positively correlated with stress, culminating in the Dead Sea surface but dropped drastically in 50- to 280-m-deep seawater. The genomic diversity pattern paralleled the pattern of sexual reproduction of fungal species across the same southward gradient of increasing stress in Israel. This parallel may suggest that diversity and sex are intertwined intimately according to the rise and fall pattern and adaptively selected by natural selection in fungal genome evolution. Future large-scale verification in micromycetes will define further the trajectories of diversity and sex in the rise and fall pattern.