Temperature structuring of microbial communities on a global scale.

Temperature is a fundamental physical constraint regulating key aspects of microbial life. Protein binding, membrane fluidity, central dogma processes, and metabolism are all tightly controlled by temperature, such that growth rate profiles across taxa and environments follow the same general curve. An open question in microbial ecology is how the effects of temperature on individual traits scale up to determine community structure and function at planetary scales.

Environmental memory alters the fitness effects of adaptive mutations in fluctuating environments.

Evolution in a static laboratory environment often proceeds via large-effect beneficial mutations that may become maladaptive in other environments. Conversely, natural settings require populations to endure environmental fluctuations. A sensible assumption is that the fitness of a lineage in a fluctuating environment is the time average of its fitness over the sequence of static conditions it encounters.

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.

Environmental fluctuations reshape an unexpected diversity-disturbance relationship in a microbial community.

Environmental disturbances have long been theorized to play a significant role in shaping the diversity and composition of ecosystems. However, an inability to specify the characteristics of a disturbance experimentally has produced an inconsistent picture of diversity-disturbance relationships (DDRs). Here, using a high-throughput programmable culture system, we subjected a soil-derived bacterial community to dilution disturbance profiles with different intensities (mean dilution rates), applied either constantly or with fluctuations of different frequencies.

Microbial communities display alternative stable states in a fluctuating environment.

The effect of environmental fluctuations is a major question in ecology. While it is widely accepted that fluctuations and other types of disturbances can increase biodiversity, there are fewer examples of other types of outcomes in a fluctuating environment. Here we explore this question with laboratory microcosms, using cocultures of two bacterial species, P.

Higher temperatures generically favour slower-growing bacterial species in multispecies communities.

Temperature is one of the fundamental environmental variables that determine the composition and function of microbial communities. However, a predictive understanding of how microbial communities respond to changes in temperature is lacking, partly because it is not obvious which aspects of microbial physiology determine whether a species could benefit from a change in the temperature. Here we incorporate how microbial growth rates change with temperature into a modified Lotka-Volterra competition model and predict that higher temperatures should-in general-favour the slower-growing species in a bacterial community.

Mortality causes universal changes in microbial community composition.

All organisms are sensitive to the abiotic environment, and a deteriorating environment can cause extinction. However, survival in a multispecies community depends upon interactions, and some species may even be favored by a harsh environment that impairs others, leading to potentially surprising community transitions as environments deteriorate. Here we combine theory and laboratory microcosms to predict how simple microbial communities will change under added mortality, controlled by varying dilution.