Patterns and Determinants of Halophilic Archaea (Class Halobacteria) Diversity in Tunisian Endorheic Salt Lakes and Sebkhet Systems

Abstract

We examined the diversity and community structure of members of the halophilic Archaea (class Halobacteria) in samples from central and southern Tunisian endorheic salt lakes and sebkhet (also known as sebkha) systems using targeted 16S rRNA gene diversity survey and quantitative PCR (qPCR) approaches. Twenty-three different samples from four distinct locations exhibiting a wide range of salinities (2% to 37%) and physical characteristics (water, salt crust, sediment, and biofilm) were examined. A total of 4,759 operational taxonomic units at the 0.03 (species-level) cutoff (OTU 0.03 s) belonging to 45 currently recognized genera were identified, with 8 to 43 genera (average, 30) identified per sample. In spite of the large number of genera detected per sample, only a limited number (i.e., 2 to 16) usually constituted the majority (>80%) of encountered sequences. Halobacteria diversity showed a strong negative correlation to salinity (Pearson correlation coefficient ‫؍‬ ؊0.92), and community structure analysis identified salinity, rather than the location or physical characteristics of the sample, as the most important factor shaping the Halobacteria community structure. The relative abundance of genera capable of biosynthesis of the compatible solute(s) trehalose or 2-sulfotrehalose decreased with increasing salinities (Pearson correlation coefficient ‫؍‬ ؊0.80). Indeed, qPCR analysis demonstrated that the Halobacteria otsB (trehalose-6-phosphatase)/16S rRNA gene ratio decreases with increasing salinities (Pearson correlation coefficient ‫؍‬ ؊0.87). The results highlight patterns and determinants of Halobacteria diversity at a previously unexplored ecosystem and indicate that genera lacking trehalose biosynthetic capabilities are more adapted to growth in and colonization of hypersaline (>25% salt) ecosystems than trehalose producers.T he class Halobacteria represents a physiologically and phylogenetically distinct lineage within the archaeal phylum Euryarchaeota. Members of the Halobacteria are encountered in a wide range of environments where their absolute requirement for salt is satisfied. Within various hypersaline (Ͼ25% salt), thalassohaline (e.g., crystallizer ponds in solar salterns), and athalassohaline (e.g., the Dead Sea, hypersaline lakes, and soda lakes) water bodies, members of the Halobacteria represent the majority of the cellular biomass (1-6). However, in environments with relatively lower salinity and/or fluctuating salinities, e.g., saline soils (salt plains and alpine salt sediments, soils adjacent to salt-processing plants), traditional Asian salted and fermented seafood products (e.g., jeotgal), and marine sponges, they usually coexist as a smaller fraction of the more diverse prokaryotic community inhabiting these settings (7-13). These habitats with moderate or low salinity and/or fluctuating salinity have been the source of species of many recently described novel Halobacteria taxa (14-18) and are partially responsible for the rapid expansion of recognized Halobacteria spp. during the ...

The biogeography of soil archaeal communities on the eastern Tibetan Plateau

“…Halobacteria abundance was recently reported to be mostly influenced by salinity:24 members of this phylum are found in high-pH soda lakes25, Mg 2+ -rich water bodies26, solar salterns3 and crystallizer ponds27. In the present study, the salinity, high pH conditions and strong sun exposure could be a large part of the reason why Halobacteria were more prevalent in the arid environments7.…”

Reducing Salinity by Flooding an Extremely Alkaline and Saline Soil Changes the Bacterial Community but Its Effect on the Archaeal Community Is Limited

“…In the Texcoco soil Natronococcus was favored by the high pH rather than salinity. Najjari et al (2015) considered Halobiforma a moderately abundant genera reaching a relative abundance of 18.8%, similar as found in the unflooded soil, in a sediment sample with 6.7% salinity. They considered Halogranum and Halorubrum as consistently abundant genera, but in this study the first was detected in only one soil sample (relative sequence abundance of 0.026%) and the relative abundance of the latter remained low (≤ 0.052%).…”

“…Natronococcus (18.28 ± 0.08%) was the most abundant genus in the Texcoco soil together with Halobiforma (9.08 ± 0.08%). Contrarily, Najjari et al (2015), while studying halophilic Archaea (Class Halobacteria) in Tunisian endorheic salt lakes and sebkhet systems ( n = 23), reported a maximum relative abundance of 1.6% for Natronococcus . The genus was absent often from samples so they considered it a rare genus with occasional low abundance.…”

Targeted and contextual redescription set exploration

“…The haloarchea (previously referred to as halobacteria), leave in the extreme environments (which is evident from the phenotype hypersalin) (Kennedy et al 2001). This also explains the further two phenotypes seafood (since it is often found in salted fish) and NaCl because of the fact that high salinity attracts the haloarchea (Najjari et al 2015).…”