Polysulfides at the core of bacterial sulfur metabolism

Polysulfides have emerged as key intermediates that organize sulfur metabolism, redox regulation and environmental adaptation in bacteria. Rather than representing minor side products, polysulfides form a dynamic chemical pool that links sulfide utilization, sulfur storage and regulatory signaling. This review provides an integrated overview of polysulfide-centered sulfur metabolism in bacteria, highlighting how polysulfides arise through multiple metabolic routes and are subsequently processed, redistributed or stored depending on physiological context. Particular emphasis is placed on the dual roles of polysulfides as both metabolic intermediates and regulatory signals, enabling cells to coordinate sulfur flux with transcriptional control and redox homeostasis. The accumulation of elemental sulfur is discussed as a context-dependent outcome of polysulfide chemistry, functioning either as a transient intermediate during sulfide oxidation or as a regulated sulfur reserve under nutrient limitation. By reinterpreting classical studies of sulfur metabolism alongside recent biochemical, genetic and genomic advances, this review underscores the ubiquity and functional importance of polysulfides in bacterial physiology. Collectively, these insights support a unifying view in which polysulfides occupy a central position in bacterial sulfur metabolism, bridging ancient sulfur-based bioenergetics with modern regulatory networks that ensure metabolic flexibility and environmental resilience.