<i>In silico</i> comparative genomic analysis of arsenic resistance operons in bacterial representatives associated with Urmia and Van lakes

Abstract Arsenic contamination poses major ecological and health risks, and microorganisms play key roles in arsenic cycling and detoxification. This study presents a comparative in silico analysis of arsenic resistance operons in representative bacterial genomes associated with two extreme ecosystems, Urmia Hypersaline Lake (Iran) and Van Soda Lake (Turkey). Six representative genomes were selected based on 16S rRNA gene sequence homology, and their operons were characterized. Both canonical and non-canonical arrangements were identified, reflecting lineage-specific adaptations and horizontal gene transfer. The predicted promoters and terminators indicate regulatory diversity among the operons. Phylogenetic analysis of 16S rRNA gene sequences from 17 isolates showed low nucleotide diversity, whereas functional genes displayed high polymorphism. Haplotype diversity was the greatest for arsR (Hd = 0.960), followed by arsB and arsC (Hd = 0.933 each). Population differentiation analysis showed a significant divergence of arsR between Urmia and Van isolates (F_ST = 0.759), highlighting its role in local adaptation to arsenic-rich environments. These findings suggest a dual strategy for microbial adaptation, maintaining conserved core operons while incorporating diverse accessory genes to broaden detoxification potential. This study provides insights into microbial survival strategies in extreme saline and soda lakes and offers a genomic framework for future functional investigations.