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, MgSO4, NaHCO3), strong oxidizers (Mg(ClO4)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.
Highlights
A significant part of the land surface of our planet is covered with hot deserts and semi-deserts [1]
The number of heterotrophic aerobic bacteria cultured from the Gibson Desert sample at 25 °C was (4 ±1) ×107 colony forming units (CFU)/g and (1.6 ±0.4) ×107 CFU/g on GPY medium and CM medium respectively
The coefficients K indicate a high proportion of culturable bacteria in both microbial communities. These values are consistent with already known literature data on microbial abundance and cultivability of bacteria isolated from arid soils [13,16,51,52] and could be interpreted as an evidence of a shallow metabolic dormancy of these bacteria and the possible metabolic activity of these communities in situ
Summary
A significant part of the land surface of our planet is covered with hot deserts and semi-deserts [1]. Due to the large areas, such ecosystems play a significant role in the biogeochemical cycles of various chemical elements and affect gas composition of the atmosphere [3]. Deserts are the habitats of organisms, that have adapted their metabolism to extremely heterogeneous and changing environmental conditions [4]. Such organisms are often valuable to biotechnology, for example, as the producers of industrial substances [5,6]. Considering the large area of arid habitats and its insufficient study, it is likely that the larger part of unexplored microorganisms’ biodiversity is still concealed in such ecotopes [6]
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