Non-viral predators of marine picocyanobacteria

The mechanisms by which the superabundant marine picocyanobacteria die are important to understanding the global carbon cycle, the structure of marine food webs, and the evolutionary pressures that have shaped microbial life in the ocean.The cross-scale systems biology framework for understanding marine picocyanobacteria is missing a key component of ecology and evolution: the diverse and widespread non-viral predators of picocyanobacteria.Prochlorococcus and Synechococcus non-viral predators are unidentified, patchy, fragile, challenging to collect, have complex life cycles, and are frequently intractable in laboratory studies.Mortality of picocyanobacteria by viruses is more well studied than mortality by non-viral predators owing to tractability of viruses in laboratory experiments and viral isolation from the wild; however, numerous unknowns still exist about viral mortality.Approaches that integrate across methodologies (e.g., in situ incubations via SCUBA combined with flow cytometry, sequencing, and predator cultivation), are promising for future work to reveal the grazing impacts of cosmopolitan non-viral predators, including protists, pelagic tunicates, and thecosome pteropods on marine picocyanobacteria ecology and evolution. The Earth’s most abundant photosynthetic cells, the picocyanobacteria – Prochlorococcus and Synechococcus – play a fundamental global role in aquatic ecosystems. The success of these picocyanobacteria is interpreted through a cross-scale systems framework that integrates bottom-up controls on growth (e.g., nutrients and light), diversity, and the selective pressures and response to predation. While viral predators are well studied and experimentally tractable, the diverse non-viral predators of picocyanobacteria are disconnected from this framework and experimentally challenging, leaving a major gap in understanding the picocyanobacteria. This review presents existing research on non-viral picocyanobacterial predators and promising research frontiers that will expand knowledge of the ecology and evolution of these crucial microorganisms. The Earth’s most abundant photosynthetic cells, the picocyanobacteria – Prochlorococcus and Synechococcus – play a fundamental global role in aquatic ecosystems. The success of these picocyanobacteria is interpreted through a cross-scale systems framework that integrates bottom-up controls on growth (e.g., nutrients and light), diversity, and the selective pressures and response to predation