Bioactive Metabolites from UV-Resistant Streptomyces alkaliterrae CH-8 in Desert Soil: In-Vitro Study on Their Potent Antioxidant and Antibiofilm Activities

The exploration of extremotolerant microorganisms from arid ecosystems offers promising avenues for novel bioactive compound discovery. In this study, a radioresistant actinobacterial strain, CH-8, was isolated from the hyper-arid soil of the Cholistan Desert, Pakistan. Phylogenetic analysis of the 16S rRNA gene revealed 99.88% similarity with Streptomyces alkaliterrae . Strain CH-8 demonstrated high oxidative and UV-B tolerance, with 78% and 60% survival under 10 mM H₂O₂ and 2712 J/m² UV-B exposure, respectively. Intracellular metabolites were extracted using methanol and purified via silica gel chromatography. The purified fraction showed strong antioxidant activity (78% DPPH scavenging), and was rich in phenolics (149 mg GAE/g) and flavonoids (2.082 mg QE/g). Crude extracts exhibited significant anti-biofilm activity against Gram-positive pathogens, achieving up to 85.4% inhibition and 88.1% eradication. Cytotoxic potential was confirmed via brine shrimp lethality assay (IC₅₀ = 19.23 µg/mL), and DNA damage protection indicated radioprotective capability. LC-MS analysis identified several bioactive compounds, including a glycosylated polyketide (m/z 575.6) resembling dynemicin L, as well as lankacidin C and lynamicin D. These findings position S. alkaliterrae CH-8 as a promising source of therapeutic secondary metabolites, and highlight the Cholistan Desert as a reservoir of untapped microbial and biochemical diversity.