The potentially non-stick SAR11 clade

This paper proposes that some free living bacteria species have adapted to have a non-stick surface in order to evade predation from filter feeders. This however is a trade of as many marine bacteria thrive in their environment through their ability to stick to nutrient rich organic particles.  The SAR11 clade which includes the species studied, Pelagibacter ubique, are the most ubiquitous in the upper ocean, it has been suggested that they may comprise between 15-60% of the total bacteria. 

Grazing in the marine environment is one of the most prominent mortality factors for bacteria. The microbial composition of the ocean is controlled by the grazing by filter feeders. Adaptation to evade this threat may be one of the reasons that the SAR11 clade is highly abundant. It is thought that they are able to slip through the mucous nets of benthic and pelagic tunicates. This study tested this theory through experiments using the pelagic relatives of the ascidians, the appendicularians. This pelagic species was used as it is unlikely that benthic bacterivory would have any significant effect on the distribution and abundance of pelagic bacterial population. Appendicularians only dominate open ocean bacterivory during temporary population blooms, yet are very important pico-planktivores. They play a central role in role in pelagic food webs as they can remove more than half of the microbial populations in a few days.

This study suggested that, Pelagibacter ubique can slip through the mucous nets of common filter feeders. This trade-off may help to explain the SAR11 clade’s success in the ocean. The biochemical, physiological and ecological roles that this adaptation has for oligotrophic bacteria would require further study. Bacterial recognition and mucociliary mechanisms are effective defence mechanisms against pathogens. A better understanding of the bacterial cell wall structure and how these mucous filters interact could have benefits beyond marine biology, making this study highly important and providing evidence that this area of study needs to be investigated more. The future importance of this study makes it incredibly interesting, further study is needed into how this adaptation may have evolved and how it may have enabled the proliferation of the species.

Referenced paper: Dadon-Pilosof, A., Conley, K.R., Jacobi, Y., Haber, M., Lombard, F., Sutherland, K.R., Steindler, L., Tikochinski, Y., Richter, M., Glöckner, F.O. and Suzuki, M.T., 2017. Surface properties of SAR11 bacteria facilitate grazing avoidance. Nature microbiology, p.1.