Warmer temperatures favor slower-growing bacteria in natural marine communities

Earth’s life-sustaining oceans harbor diverse bacterial communities that
display varying composition across time and space. While particular
patterns of variation have been linked to a range of factors, unifying
rules are lacking, preventing the prediction of future changes. Here,
analyzing the distribution of fast- and slow-growing bacteria in ocean
datasets spanning seasons, latitude, and depth, we show that higher
seawater temperatures universally favor slower-growing taxa, in agreement
with theoretical predictions of how temperature-dependent growth rates
differentially modulate the impact of mortality on species abundances.
Changes in bacterial community structure promoted by temperature are
independent of variations in nutrients along spatial and temporal
gradients. Our results help explain why slow growers dominate at the ocean
surface, during summer, and near the tropics and provide a framework to
understand how bacterial communities will change in a warmer world.