Exploring the Biodiversity of Halophilic Actinobacteria from the Ramsar Wetland of Lake Naïla (Morocco): Taxonomic Diversity and Biotechnological Potential

Extreme saline ecosystems represent valuable reservoirs of unexplored microbial diversity with significant ecological and biotechnological importance. The sebkha of Lake Naïla, a Ramsar-protected coastal wetland in southern Morocco, remains largely uncharacterized in terms of its microbial communities. Sediment samples were collected at a depth of 2.78 m from the study site using a multibeam echosounder. In this study, seven halophilic actinobacterial isolates were recovered from saline sediments using selective culture media and identified by 16S rRNA gene sequencing. The isolates belonged to three genera: Streptomyces (five isolates), Nocardiopsis (one isolate), and Prauserella (one isolate), highlighting the taxonomic diversity of this extreme habitat. Although members of these genera have previously been reported from hypersaline environments elsewhere, the present study constitutes the first report of the genus Nocardiopsis in Morocco. Functional screening revealed that all isolates expressed at least one plant growth-promoting trait. Nocardiopsis sp. strain 42 exhibited the highest indole-3-acetic acid (IAA) production (282 μg mL⁻¹), whereas Streptomyces strains 39, 43, and 48 showed the greatest phosphate-solubilizing activity (>20 mg L⁻¹). The highest siderophore production was recorded for Streptomyces thermocarboxydus strain 41 (83%), while strains 42, 43, and 48 showed strong ammonia production. To screen the isolated actinobacteria against pathogens, the antimicrobial activity was assessed using the agar diffusion method. Three Streptomyces isolates displayed remarkable antimicrobial activity against important human pathogens, including Enterococcus faecalis, Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Klebsiella aerogenes, Aspergillus brasiliensis, and Candida albicans, with inhibition zones reaching 24 mm against S. aureus. GC–MS analysis of the most active isolate (Streptomyces sp. strain 43) revealed a complex metabolite profile containing more than 100 compounds, with 1,2-propanediol and nonanal identified as the major bioactive metabolites. These findings demonstrate that the sebkha of Lake Naïla constitutes an important hotspot of halophilic actinobacterial diversity and a promising source of microorganisms with ecological functions and valuable antimicrobial and plant growth-promoting properties. This study contributes to the understanding of microbial biodiversity in North African saline ecosystems while emphasizing their potential for sustainable agricultural and pharmaceutical applications.