Several wetlands with extreme environmental conditions, have been the focus of extensive research to describe microbial diversity and biotechnological potential. The arid and hypersaline Chott El Jerid (Tunisia), with hypersaline conditions, was studied to screen bacteria an archaea isolates for the accumulation of polyhydroxyalkanoates inclusions (Ben Abdallah et al 2020). The hypersaline geothermal area of Dallol in the desert of Danakil (Ethiopia), holding chaotropic conditions related to Mg++/Ca++ -dominated brines, hyperacidity and elevated temperatures allowed identifying exceptionally diverse and abundant ultrasmall archaea (Belilla et al 2019). In Algeria, the salty to moderately salty wetland dayat Morsli, near Oran, facing many years of anthropogenic pollution, was investigated for physicochemical and biological yearly dynamics in the view of rehabilitation possibilities (Ben Bayer et al 2019); recent investigation of The Great Sebkha of Oran, a hypersaline lake, allowed characterizing 17 halotolerant bacterial isolate as promising sources of important molecules (Saibi et al 2022); and the hypersaline Saharian chott Zehrez-Chergui was investigated using a combination of cultivable and non-cultivable method in search of soil halophilic archaea (Hassani et al 2022).
The present study constitutes the first investigation of Chott Ech Chergui (Algeria) and provides one of the largest wetlands of the north African desert with physico-chemical and bacteriological characteristics. Water deficiency is thus the main constraint of this wetland, which occurs seasonally in some areas or constitutes a chronic stress in others, leading to dried out sites that prevented from appropriate sampling. At the exception of site n°3 (Large Sebkha), that showed high level of organic matter contents, the surface waters of Chott Ech Chergui are generally oligotrophic and observed changes in water chemistry are mainly related to meteorological factors. The water nutrient dynamic is affected by soil leaching that follows periods of rainfalls (Loudière and Gourbesville 2020), and also by water evaporation at the dry summer season that concentrate nutrients (nitrate, nitrite, orthophosphate) as previously reported by the United Nation report (Hazzab 2011; Ouali et al 2018).
Our study distinguishes four key habitats in the Chott Ech Chergui wetland suitable for the isolation of extremophile bacteria. The first are the hot springs (sites n°1 and n°4), which have a constant water temperature of 37–40°C throughout the year, a high oligotrophy level with low contents of organic matter, nitrogen, and phosphorus. According to the classification of (Skopljak et al 2006), these thermal waters are dominated by chlorides and calcium and, unlike other thermal springs in the region (Hazzab 2011; Ouali et al 2018), theyalso show elevated contents of sulfate and sodium. Among the eight thermal springs relevant of the public sector in Algeria, only one thermal spring (Hammam Charef, located ~ 200 km east of Chott Ech Chergui) has the most similar water chemistry (Ouali et al 2018; Fig. S1 and S2). This extreme habitat, characterized by high temperatures and by oligotrophic conditions, imposes strong physiological constraints that should limit bacterial metabolism, growth and multiplication. The second habitat is hypersaline (site n°3) showing high salinity levels in the sediment (up to 380 g.L− 1; Table S2) that drive elevated but fluctuating salt contents in water (reaching 80 g.L− 1) in relation to regular supply with freshwater, hot springs and rain. In this habitat, high concentrations of chloride, magnesium, calcium, nitrites, nitrates, orthophosphates, and ammonium should favor bacterial growth and sustain diversification of thermo- and halo- tolerant microbiota. In comparison to other hypersaline habitats of north Africa, the three permanent arid salt lakes in the Oued Righ valley (northeastern Algeria) showed the same type of chlorinated and calcium sulphate waters (Gouasmia et al 2016); while the four arid salt lakes of Tunisia showed differences of water minerality and nutrient content, in relation to chlorides and sodium/potassium dominance (Kbir-Ariguib et al 2001). The third habitat (sites n°6 and n°7), in addition to hypersaline characteristics of both water and sediments (Table S2), is characterized by elevated pH values, suitable for the development of alkaliphile microorganisms. The fourth habitat (sites n°2 and n°5) given its condition at the confluence of all three previous habitats, showed average levels of nutrient, pH, salinity and temperature values, making of it the most hospitable habitat of Chott Ech Chergui that should hold abundant and diversified microbial life.
Our sampling campaign successfully allowed the bacteriological, biochemical and molecular characterization of several extremophile isolates affiliated to the Proteobacteria (Table S1), with several strains regrouped to genus Chromohalobacter and Salinicola and to the Firmicutes, with several strains regrouped to genus Bacillus, Geobacillus, Staphylococcus, Exigubacterium, Lysinibacillus and Virgibacillus. Such bacterial taxa were also isolated from saline ecosystems of northeastern Algeria (Menasria et al 2019), from salterns in Korea (Lee et al 2012), from various saline habitats in India (Kumar et al 2012), from saline and hypersaline lakes in the Qinghai Province of China (Jiang et al 2018) and more closely, in The Great Sebkha of Oran (Saibi et al 2022).
All these bacterial isolates had the ability to thrive at alkaline pH and high salt concentrations. The bacterial isolates affiliated to the Firmicutes formed a group of halotolerant bacteria, to the exception of the Virgibacillus strain OM301613 considered halophilic, like all bacterial isolates affiliated to the Proteobacteria. According to the classification of alkaliphile (Mevada et al 2022), thirty bacterial isolates were considered facultative alkaliphiles, while nine were considered alkalitolerant.
Three bacterial isolates affiliated to the genus Exiguobacterium (strains OM301601, OM301581 and OM301607) can thrive at temperatures ranging from 4°C to 60°C and are thus considered psychro-thermotolerant. One bacterial isolate affiliated to the genus Geobacillus (strain OM301608) is considered thermophilic as it shows the ability to grow at 100°C, while all other bacterial isolates are considered meso-thermotolerant as they show abilities to grow at temperature ranging from 15°C to 60°C. The recovery of thermotolerant bacteria affiliated to the genus Bacillus and Geobacillus is not surprising as they have often been described as abundant members of microbial community living in thermal environments (Amin et al 2018; Narsing Rao et al 2018; Panosyan et al 2018; Xian et al 2018; Belilla et al 2019 and Saghatelyan et al, 2021).
Although all bacterial isolates were polyextremophile, their site of origin determines their degree of tolerance to the three main constraint of Chott Ech Chergui wetland (temperature, alkalinity and salinity). For instance, strains that can grow at high salt concentrations were found in the second and third habitats (sites 3 and 6) characterized by salinity and alkalinity, respectively; and those that can grow at high temperature were found in the first habitat (sites 1 and 4) characterized by temperatures and in the fourth habitat (sites 2 and 5) showing intermediate conditions. However, alkaliphilic and alkaline-tolerant strains were found in all four habitats.
Several bacterial isolates of our collection were shown to express enzymatic activities valuable in biotechnology (such as lipases and amylases) in a large range of temperature or salt concentrations. These initial bacteriological test open perspective of biochemical investigation of the corresponding bioactive molecules these bacterial isolates produce (Boyadzhieva et al 2018; Qiu et al 2021; Pham et al 2021) and highlights the biotechnological potential of Chott Ech Chergui wetland as a reservoir of polyextremophile bacterial isolates.