Predation in microbial communities: gradients of nutritive killing.

Long before nature was 'red in tooth and claw', it was sundered by nano-spears and seeping poisons. Microorganisms were the first predators, and predation has since deeply shaped all major branches of life - from individual traits to collective systems, community dynamics and major evolutionary transitions. Yet, we have only begun to understand how microbial predation influences the genetics, morphology, behaviour, ecology and evolution of microorganisms in natural communities and, in turn, the macroscopic biosphere. With the field advancing rapidly on diverse fronts, integrative conceptual frameworks, questions and research approaches are needed to promote synthetic development of the field. In this Review, we explore the remarkably diverse forms of microbial predation that have evolved so far, considering organismal traits and their molecular foundations alongside the evolutionary ecology of predator-prey interactions in community contexts. Building on a process-based definition, forms of microbial predation are conceptualized along gradients, including gradients of evolutionary adaptedness for predation and of privatization of prey-derived nutrients. Important future research themes include predation origins and early stages of predatory adaptation, effects of diverse forms of predation on community diversity and stability, predator-prey co-evolution in complex communities, and multi-approach development of unicellular predators as biocontrol agents.