Abstract:
The study of extremophilic bacteria provides new keys to understanding the processes of
life in extreme conditions and knows the different mechanisms developed to support them.
Depending on the extreme conditions, extremophilic microorganisms may be:
thermophilic, halophilic, psychrophilic, alkalophilic, acidophilic or piezophilic or
polyextremophilic for two or more factors.
Our goal is to isolate extremophilic bacteria belonging to the Bacillaceae family, from the
Saharan soil of Metlili region (Sabkha), and study their tolerance to different culture
conditions: salinity and temperature. Two thermophilic bacterial strains were isolated at 60
° C on nutrient agar medium after thermal treatment in an autoclave for 10 min at 120 ° C
to remove all vegetative forms. Both strains were chosen for physiological, biochemical
and phylogenetic study.
The isolated strains N19 and B19 are in the form of rods, mobile, Gram-positive,
aerobically strict, capable of forming endospores. In addition, they are tolerant to
concentrations of NaCl 0-4% (w / v), at pH 5-9, and at different temperature values 25-70 °
C.
The biochemical identification of the isolates by the classical tests showed that they are
catalase positive, oxidase positive and then by the galleries API 20E and API 50CHB, and
after the treatment of the results obtained by the 2 programs: Excel Identification Program
(EIP) and ABIS online, the results show that the strains belong to different types of Bacilus
species such as (Bacillus firmus, Bacillus cereus 'group 2') and as (Brevibacillus brevis,
Bacillus sporothermodurans, Bacillus smithlii, Geobacillus stearothermophilus, Bacillus
cereus) with percentage or different probability.
In order to clearly identify these strains B19, N19, we realized the molecular study for both
strains, by sequencing the genomic portion of 16S DNA, and after processing the results
obtained by the MEGA X program, we found that the percentage of similarity is 98.9% for
both strains with the closely related species Geobacillus caldoxylosilyticus.
