Soil bacterial communities of Sahara and Gibson deserts: Physiological and taxonomical characteristics

Abstract

The purpose of this research was to investigate the structure of soil bacteria communities present in the Gibson (Australia) and the Sahara (Egypt) deserts, as well as to estimate strain survivability under different environmental factors. It should be noticed that the screening of bacterial resistance to wide spectra of principally different stress conditions was performed for the first time. Experiments were conducted with culturable bacterial communities. Strains were identified using 16S rRNA sequencing, and stress-tolerance was estimated by growing strains in various nutrient media. In order to characterize the community the epifluorescent microscopy and multisubstrate testing were also performed. High bacterial abundance in the desert soils was detected, and there was seen a significant proportion of culturable cells. The close numbers of psychotropic and mesophilic bacteria in arid ecosystems were revealed. The representatives of the Actinobacteria phylum were dominant in the microbial communities, and Firmicutes , Proteobacteria , and Bacteroidetes phyla representatives were also identified. Tolerance of the axenic bacterial cultures, isolated from arid desert ecotopes, to temperature, pH, salts (KCl, NaCl, MgSO 4 , NaHCO 3 ), strong oxidizers (Mg(ClO 4 ) 2 ), and antibiotics (ampicillin, cephalexin, chloramphenicol, tetracycline, doxycycline, kanamycin, rifampicin) was studied. The bacterial isolates were characterized by polyextremotolerance and by the ability to maintain metabolic activity in vitro while influenced by a wide range of physicochemical and biotic factors.

Stress-Tolerance and Taxonomy of Culturable Bacterial Communities Isolated from a Central Mojave Desert Soil Sample

“…It is notable that the numbers of bacteria cultured at 10 • C and 25 • C were virtually equal. Based on these data, it is possible to assume that there is a high proportion of strains with psychrotolerant properties in the investigated soil, as was previously found for bacteria isolated from the Sahara and the Gibson Desert soils [44].…”

“…The bacteria of genera Arthrobacter, Bacillus, Kocuria, Leucobacter, Massilia, Mycetocola, Microbacterium, Paracoccus, Planomicrobium, Pseudarthrobacter, Rufibacter, Sphingomonas, and Streptomyces were previously isolated from other hot deserts [44,[63][64][65]. Bacteria of the genus Agrococcus were previously cultured from cold deserts [66].…”

“…Peptone Yeast Glucose (PYG) medium rich in various carbon sources and nutrients (glucose-1 g/L, peptone-2 g/L, yeast extract-1 g/L, tryptone-1 g/L, agar-20 g/L) and modified Czapek (CM) medium [44] were used for bacteria culturing and isolation. Dilutions of the soil sample in sterile 0.01 M phosphate-saline buffer solution (pH 7.4, 0.137 M NaCl, 0.0027M KCl) in tenfold dilution step were plated on the solid nutrient media in three replicates [45].…”

“…Antibiotic resistance was determined on nutrient media containing ampicillin (Amp), cephalexin (Ceph), chloramphenicol (Chl), tetracycline (Tet), doxycycline (Dox), kanamycin (Kan), or rifampicin (Rif ) (Belmed, Russia) with a final concentration of 100 µg/mL. All tests (except for resistance to temperature) were carried out at a temperature of 25 • C [44]. The growth was registered on the tenth day after inoculation for the cultures cultivated at temperatures of 10, 25, 37, 45, and 50 • C; for cultures growing at temperatures of 2 and 4 • C the incubation period was 60 and 30 days, respectively.…”

“…Growth registering was performed using a Sunrise (Tecan, Menendov, Switzerland) plate photometer at a wavelength λ = 620 nm: The plates were measured immediately after inoculation and after incubation period. Detailed protocol of physiological assays is described in [44].…”