Abstract:

This study provides a comprehensive analysis of the distribution, abundance, and environmental adaptability of Actinobacteria in the soils of Al-Haniya, a coastal agricultural region in Libya characterized by saline-alkaline conditions. We investigated the vertical (0–10 cm depth) and horizontal spatial distribution of Actinobacteria across 150 subplots, comparing rhizospheric and bulk soil microbiomes. Using standardized culture-dependent methods, we quantified Actinobacteria populations and identified dominant genera through morphological and biochemical assays. Key abiotic factors—temperature (25–40°C), pH (4–8), and salinity (0.1–5 g/L of CaCl₂, NaCl, MgCl₂)—were systematically evaluated for their effects on Actinobacteria growth kinetics. Our results revealed that Actinobacteria populations were significantly higher in rhizospheric soil (8.26 × 10⁷ CFU/g) compared to bulk soil (7.42 × 10⁷ CFU/g), with Streptomyces constituting 70–90% of isolates. Optimal growth conditions were observed at 30°C and pH 7, while no growth occurred at pH ≤5. Remarkably, Actinobacteria demonstrated notable salt tolerance, with CaCl₂ enhancing growth up to 47 × 10⁷ CFU/g at 5 g/L.Statistical analyses (ANOVA, LSD p < 0.05) confirmed significant correlations between Actinobacteria abundance and soil properties, particularly organic matter content (1.33–2.75%) and clay texture (41–49%). The study also identified a negative relationship between salinity and phosphorus availability, highlighting nutrient cycling dynamics. These findings underscore the ecological resilience of Actinobacteria in marginal soils and their potential applications insaline agriculture (as bioinoculants to improve cropstresstolerance);bioremediation (organic matter decomposition in degraded soils);antibioticdiscovery (exploiting Streptomyces dominance).This work provides the first detailed characterization of Actinobacteria in Libyan coastal soils and establishes a foundation for future research on microbial-assisted soil rehabilitation in arid regions.