Thermo-halotolerant mycelial bacteria from Algerian soils: Isolation, taxonomy and antagonistic properties

Abstract We studied the biodiversity and growth inhibitory potential of thermo-halotolerant mycelial bacteria isolated from Algerian soils. A total of 55 strains were isolated from 11 soil samples at 3 different provinces in Algeria. Some strains possessed the morphological characteristics of Saccharomonospora (24 strains) and Saccharopolyspora (4 strains). However, the morphological characteristics of 5 strains matched those described for members of the family Thermoactinomycetaceae. Furthermore, 22 strains belong to unknown genera have been isolated. The isolation of thermo-halotolerant mycelial bacteria was carried out on nutrient agar medium supplemented with 10% NaCl, under incubation for 10 days at 52 °C. 16S rRNA gene analyses, of 15 out of 55 thermo-halotolerant mycelial bacteria, indicated that one strain belongs to Saccharopolyspora, nine strains belong to Saccharomonospora and five strains belong to Melghirimyces. An assessment of the biological properties of these 15 thermo-halotolerant actinomycetes, evaluated by the cylinder plate method against 15 target-microorganisms, showed moderate to strong growth inhibitory activities against bacteria, micro-fungi or yeasts. We noticed a variation in diameters of inhibition between actinomycetes tested. Moreover, these values were different based on the culture medium (GYEA or BM) and also on the concentration of NaCl (1% or 5%). The strongest growth inhibitory activity was recorded against Listeria monocytogenes ATCC 13932 (26 mm), Micrococcus luteus ATCC 9314 (24 mm) and Klebsiella pneumoniae E40 (24 mm). These results indicated the importance of further exploration of thermo-halotolerant mycelial bacteria for potentially new antimicrobial compounds.