Physiological and genomic insights into abiotic stress of halophilic archaeon Natrinema altunense 4.1R isolated from a saline ecosystem of Tunisian desert

Abstract

Halophilic archaea are polyextremophiles with the ability to withstand fluctuations in salinity, high levels of ultraviolet radiation, and oxidative stress, allowing them to survive in a wide range of environments and making them an excellent model for astrobiological research. Natrinema altunense 4.1R is a halophilic archaeon isolated from the endorheic saline lake systems, Sebkhas, located in arid and semi-arid regions of Tunisia. It is an ecosystem characterized by periodic flooding from subsurface groundwater and fluctuating salinities. Here, we assess the physiological responses and genomic characterization of N. altunense 4.1R to UV-C radiation, as well as osmotic and oxidative stresses. Results showed that the 4.1R strain is able to survive up to 36% of salinity, up to 180 J/m2 to UV-C radiation, and at 50 mM of H2O2, a resistance profile similar to Halobacterium salinarum, a strain often used as UV-C resistant model. In order to understand the genetic determinants of N. altunense 4.1R survival strategy, we sequenced and analyzed its genome. Results showed multiple gene copies of osmotic stress, oxidative stress, and DNA repair response mechanisms supporting its survivability at extreme salinities and radiations. Indeed, the 3D molecular structures of seven proteins related to responses to UV-C radiation (excinucleases UvrA, UvrB, and UvrC, and photolyase), saline stress (trehalose-6-phosphate synthase OtsA and trehalose-phosphatase OtsB), and oxidative stress (superoxide dismutase SOD) were constructed by homology modeling. This study extends the abiotic stress range for the species N. altunense and adds to the repertoire of UV and oxidative stress resistance genes generally known from haloarchaeon.

Metataxonomic analysis of halophilic archaea community in two geothermal springs sources in southern Tunisian Sahara

“…Further work is recommended to test such a hypothesis. To adapt to the low salt environment, halophilic archaea use a variety of organic solutes to counter external osmotic pressure including amino acids and derivatives, polyols, and derivatives, sugars (trehalose), betaines and ectoine (Youssef et al 2014; Najjari et al 2015; Najjari et al 2023). Indeed, a correlation between intracellular accumulation of compatible solutes and growth at supraoptimal temperatures has been observed in halotolerant or slightly halophilic (hyper) thermophiles, indicating that these solutes could act in a thermostabilization function (Hensel and König 1988; Martins and Santos 1995; Ramos et al 1997; Da Costa et al 1998; Pais et al 2005).…”