Cells collectively reshape habitability of temperature by helping each other replicate

SUMMARY How the rising global temperatures affect organisms is a timely question. The conventional view is that high temperatures cause microbes to replicate slowly or die, both autonomously. Yet, microbes co-exist as a population, raising the underexplored question of whether they can cooperatively combat rising temperatures. Here we show that, at high temperatures, budding yeasts help each other and future generations of cells replicate by secreting and extracellularly accumulating glutathione - a ubiquitous heat-damage-reducing antioxidant. Yeasts thereby collectively delay and can halt population extinctions at high temperatures. As a surprising consequence, even for the same temperature, a yeast population can either exponentially grow, never grow, or grow after unpredictable durations (hours-to-days) of stasis, depending on its population density. Despite the conventional theory stating that heat-shocked cells autonomously die and cannot stop population extinctions, we found that non-growing yeast-populations at high temperatures - due to cells cooperatively accumulating extracellular glutathione - continuously decelerate and can eventually stop their approach to extinction, with higher population-densities stopping faster. We show that exporting glutathione, but not importing, is required for yeasts to survive high temperatures. Thus, cooperatively eliminating harmful extracellular agents – not glutathione’s actions inside individual cells – is both necessary and sufficient for surviving high temperatures. We developed a mathematical model - which is generally applicable to any cells that cooperatively replicate by secreting molecules - that recapitulates all these features. These results show how cells can cooperatively extend boundaries of life-permitting temperatures.