Microbial Diversity and Biogeochemical Cycling in Red Sea Hydrothermal Vents: A Review of an Iron-Rich, Low-Temperature Hydrothermal System

Hydrothermal vents are globally significant ecosystems that host diverse microbial communities responsible for driving major biogeochemical cycles. While most known vent systems are characterized by high-temperature sulfide-rich emissions, the Red Sea presents a uniquely oligotrophic and iron-dominated hydrothermal environment. Recent discoveries at the Hatiba Mons volcano, the first active hydrothermal vent field identified in the central Red Sea, have revealed extensive iron-oxide mounds, warm vent fluids (~40°C), and abundant microbial mats.This review synthesizes current knowledge on the microbial diversity and metabolic capabilities of Red Sea hydrothermal vents, integrating recent findings from metagenomics, metabarcode analyses, and comparative genomics with global literature on vent microbiology. Microbial communities in this region are dominated by novel and deeply branching taxa from Chloroflexi, Bathyarchaeia, Pseudomonadota, and Thermoproteota, many of which remain unclassified at the genus level. Iron cycling emerges as the central metabolic axis, with widespread distribution of genes involved in Fe(II) oxidation (cyc2, cyc1, foxEYZ) and Fe(III) reduction (mtrABC, DFE_04xx family, flavin-mediated extracellular electron transfer). Unlike sulfur-rich vents, sulfur metabolism appears fragmented and taxonomically dispersed, reflecting the low sulfur availability in Red Sea vent deposits. Nitrogen cycling involves a decentralized network of nitrifiers, denitrifiers, and DNRA-capable microbes, while carbon fixation is predominantly mediated via the Wood Ljungdahl pathway in both bacterial Chloroflexi and archaeal Bathyarchaeia. Comparative analyses show that Red Sea vents differ markedly from Pacific and Atlantic systems in community composition, metabolic architecture, and geochemical constraints. Collectively, the Red Sea hydrothermal vents represent a unique model for studying metal-driven microbial ecosystems, extremophilic adaptation, and biogeochemical cycling in nutrient-poor, iron-rich marine environments.