Genomic and Phenotypic Characterization of Sandstorm-Derived Airborne Bacillus Strains Reveals Diverse Biosynthetic...

Background/Objectives: Bacillus spp. are often isolated from airborne microbiota. Five Bacillus strains (AD12-16) isolated from dust during a sandstorm in Kuwait were characterized for their potential to produce antimicrobial compounds, biosurfactants and siderophores by genotypic and phenotypic approaches. Methods: Whole-genome sequencing was performed, and biosynthetic gene clusters (BGCs) were predicted using antiSMASH. Antimicrobial activities were determined by agar-well diffusion assays. Siderophore and biosurfactant production were determined by Arnow's and drop-collapse assays, respectively. The active metabolites were separated, fractionated, and analyzed by minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and LC-MS/MS. Results: Genome mining identified many BGCs associated with known secondary metabolites such as bacillibactin and bacilysin, as well as a number of unassigned clusters. The isolates exhibited distinct antimicrobial profiles, with Bacillus subtilis AD16 displaying the highest antimicrobial activity against multidrug-resistant pathogens. Biosurfactant- and siderophore-associated activities varied among the isolates. Active fractions demonstrated bactericidal activity, while LC-MS/MS analysis revealed molecular features tentatively assigned to siderophore- and lipopeptide-associated metabolite classes based on accurate mass and MS/MS fragmentation patterns. Conclusions: The combination of unassigned BGCs, antimicrobial activity, and incompletely characterized molecular features highlights unexplored biosynthetic potential in sandstorm-derived Bacillus. Further purification and structural characterization are required to establish the identities and biological functions of the active metabolites.