: The present work was carried out on 133 halophilic strains isolated on MGM (Modified Growth Medium) medium with 12 and 23% (w/v) of salt. A screening of the extracellular proteolytic activities, carried out on the same medium supplemented with casein or gelatin at 1% (w/v), allowed us to select 24 bacterial and 21 archaeal strains presenting a precipitate around the colonies for casein and/or a translucent halo (after addition of Frazier’s reagent) for gelatin. The enzymatic test was performed on liquid medium in microculture in a 2 mL Eppendorf tube. The assay of the proteolytic activity, using Azocasein as substrate, followed two protocols—the first with PBS and the second with Tris HCl, with positive and negative controls—and demonstrated interesting results for 10 strains among the 45 tested including five bacteria and five archaea. These underwent morphological, physiological and molecular characterizations based on amplification and sequencing of the 16S ribosomal RNA gene.

Halophiles are microorganisms that inhabit saline and hypersaline environments, requiring salinity to survive in such extreme conditions. These microorganisms are mainly researched for their biotechnological potential. This study aims to investigate the phenology of the studied strain, Idiomarina loihiensis, and to demonstrate its extracellular proteolytic activity, as well as the production of a protease via batch fermentation in halophilic microorganisms. Macroscopic studies revealed small colonies (≤5 mm) with a convex spherical structure, regular outline, smooth surface, and color ranging from beige to opaque cream. Protease production was investigated in high-salinity conditions with a moderately halophilic bacterium using basal media with varying nitrogen sources. This study found that the highest proteolytic activity occurred in media with tryptone and casein peptone as nitrogen sources, at pH 10, a temperature of 70 °C, and 22.5% salt concentration. The results also demonstrated that the studied protease was a thermostable enzyme.