Genomic traits associated with copiotrophy decouple from maximum growth rate predictions along temperature gradients.

Maximum growth rate is often used as a primary axis of functional variation in studies of microorganisms, in part because emerging tools make it straightforward to estimate from genomic and metagenomic data. However, temperature, via its influence on reaction kinetics, may act as a confounder in studies that measure genomic signatures of growth optimization across environments. Observations suggest that growth optimization need not always indicate rapid growth. For example, strong temperature gradients are the norm across much of the world's oceans, where deep-ocean microbes show elevated signals of genomic growth optimization relative to the faster-growing communities at the surface. Looking across environments, we find a negative relationship between genomic growth optimization and optimal growth temperature, leading to the potential decoupling of genomic traits associated with copiotrophy from maximum growth rate, particularly when measured along a temperature gradient. Our results suggest that, as a result of temperature's confounding effects, genomic signatures of growth optimization often better predict the ecological roles and functional genomic content of microorganisms than do growth rates themselves. Finally, we suggest reframing copiotrophy as growth beyond a thermodynamic baseline maximum growth rate, rather than in relation to a static rate cutoff.