Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 9 6 2018 01 26 331 337 EN Somaye Mazkour Department of Food Hygiene and Public Health, School of Veterinary Medicine, Shiraz University, Shiraz, Iran Saeid Hosseinzadeh Department of Food Hygiene and Public Health, School of Veterinary Medicine, Shiraz University, Shiraz, Iran Seyed Shahram Shekarforoush Department of Food Hygiene and Public Health, School of Veterinary Medicine, Shiraz University, Shiraz, Iran 2017 07 21 2017 12 15 Background and Objectives: In the present study, the Lut Desert, Iran was chosen as one of the hottest places in the world (with the recorded temperature of 70.7°C during 2003-2009) to find out whether any heat-resistant microorganisms were present in the soil. Materials and Methods: The samples were collected from surface and depth of three identified places of Gandom Beryan in the Lut Desert. Chemical analysis and enumeration of the total bacteria, yeasts and molds were performed. Four selective culture media were employed to isolate the filamentous actinomycetes. The suspected colonies were further confirmed using PCR assay. Then the culture cell-free-supernatants (CFS) of isolates were used to investigate their antimicrobial activity against Staphylococcus aureus, Bacillus cereus, Salmonella Typhimurium and Escherichia coli. Results: Chemical analysis of the samples included moisture (0.2-0.9%), ash (85-91%), organic materials (8.3-14.4%), pH (7.59-9.40) and electrical conductivity (380-2000 µS/cm). The number of isolated bacteria and molds varied from 0-20 to 0-40 CFU/g, respectively. Number of Actinomycetes isolated from the soil samples were between 0-12.2 CFU/g. Nine isolated colonies were identified as filamentous Actinomycetes. To determine the possibility of antimicrobial peptides, the CFS (cell-free supernatant) was firstly neutralized by NaOH and catalase. The results showed that none of the CFS of the isolates was effective against E. coli, S. Typhimurium and S. aureus, while the maximum inhibitory effect was investigated on B. cereus, which was 33.1%±1.19% (mean ± SD). Conclusion: The results of the current study imply the presence of rare heat-resistant microorganisms in the soil of Gandom Beryan which may be further used to find out more about the function of natural bioactive compounds. Actinomycetes, as extremophile microorganisms, have shown the greatest genomic and metabolic diversity, as such the discovery of the novel Actinomycetes as a source of secondary metabolites is essential. https://ijm.tums.ac.ir/index.php/ijm/article/view/1437 https://ijm.tums.ac.ir/index.php/ijm/article/download/1437/762