Transitory planktonic attachments enhance nutrient transport to the host and symbiont cells

Acquiring nutrients and disposing of waste are among the most basic factors affecting the fitness of all living organisms. Understanding the mechanisms developed by planktonic microorganisms to meet these challenges is important to many fields of science from evolution to ecosystem ecology. Ciliated protistan epibionts, such as the Vorticella sp., attach to solid surfaces and produce advective feeding currents that transport nutrients. Unicellular organisms with limited motility and ability to generate flows, such as the diatom Coscinodiscus wailesii, rely in principle on diffusion. The advantages and limitations of advective and diffusive nutrient transport are well documented. However, it has not been generally appreciated that transitory attachments of ciliated epibionts to non-motile cells provide mutual benefits in terms of increased nutrient flux to both parties. Here we present new evidence demonstrating the hydrodynamic basis of mutual benefits for both a ciliate epibiont and its diatom host. These findings expand our understanding of the importance of transitory symbiotic interactions among microbes.