From dividing to dormant: embracing the full activity spectrum for environmental microorganisms.

SUMMARYMicroorganisms can cope with stress by entering dormancy, a viable state of reduced metabolic activity that enables persistence, dispersal, and long-term survival. However, microbial life in environmental systems is best understood as a spectrum of metabolic activity, spanning from highly active, dividing cells to deeply dormant phenotypes. This spectrum reflects dynamic survival strategies under fluctuating conditions, with critical implications for ecosystem stability, gene dissemination, and resilience to disturbances in natural and human-influenced systems. Yet, microbial activity is often treated as binary (active vs. dormant), oversimplifying a biological continuity that remains technically difficult to quantify. Here, we synthesize advances in microbial dormancy to reconceptualize activity as a spectrum. We review current and emerging methods to quantify environmental activity, linking each to the Central Dogma of molecular biology (DNA to RNA to protein) to guide interpretation along a generalizable continuum. Through a literature synthesis of terrestrial, aquatic, and wastewater treatment ecosystems, we compare how methods estimate active cells and populations. We recommend standardized reporting of total community size, active cell abundance, and proportional activity to enrich the interpretation of microbiome 'omics data, with activity intensity and active-inactive switching providing deeper insights. To achieve this, we advocate for increased accessibility and throughput of precise activity-discriminating technologies, alongside renewed use of reliable methods like direct cell counts and activity stains. Adopting this spectrum-based perspective will improve our ability to tackle key societal challenges, such as understanding microbial contributions to ecosystem function under climate change and gene dispersal at human-environment interfaces.