A Marine Photosynthetic Pair: Synechococcus WH8109 and Cyanophage Syn5

Jacqueline Piret, PhD

I had the good fortune to spend time in the King Lab as a visitor from across the river. I had earned my Ph.D. (1981) at MIT in the Industrial Microbiology Lab of Arny Demain, then spent three postdoc years in the UK and Switzerland before accepting a faculty job in the Biology Department at Northeastern University in Boston.

Jon will not remember this, but as a graduate student working long hours on the ground floor of Building 56, I would encounter him in our hallway. Unlike most MIT faculty, in my experience, he would actually stop and say hello – small gestures very appreciated by a stressed grad student and my first clue that Jon would be a good guy to work with.

Sure enough, much later, I spent two happy sabbaticals (Spring 2008 and 2014-15) in Jon’s lab. I joined a project with Peter Weigele, Welkin Pope and Cammie Haase-Pettingell studying the “horned” (5) marine cyanophage Syn5 and its abundant open ocean host Synechococcus WH8109, as an experimental system for the study of marine photosynthetic cyanobacteria. Peter and Welkin had figured out how to propagate Syn5 in its host in liquid culture – cyanobacteria form strikingly colorful cultures! Cammie and I developed a plaque assay for Syn5 – as I recall it took us a while because the plaques grew very large very quickly, clearing the plates. Once we slowed the process down we had a lovely assay to quantitate Syn5.

With host and phage methods in place, and in collaboration with the cryo-EM group of Wah Chiu (Baylor), it was possible in subsequent years to pursue a detailed characterization of the structure of Syn5, its intracellular assembly and DNA packaging, establishing this phage-host pair as a model to study the physiology and ecology of these important oxygenic marine microorganisms. Wah’s group elucidated phage assembly intermediates (1). Jon co-advised my doctoral student, Dessy Raytcheva as she characterized the Syn5 life cycle, cloning structural genes and tracking novel Syn5 proteins (2,3). This showed that Syn5 assembles through scaffold-containing procapsid intermediates — suggesting that the enteric bacteriophages inherited this assembly pathway from more ancient bacteriophages such as cyanophages (4).

  1. Dai W, Fu C, Raytcheva D, Flanagan J, Khant HA, Liu X, Rochat RH, Haase-Pettingell C, Piret J, Ludtke SJ, Nagayama K, Schmid MF, King JA, Chiu W. 2013. Visualizing Virus assembly intermediates inside marine cyanobacteria. Nature doi: 10.1038/nature12604.
  2. Gipson P, Baker ML, Raytcheva D, Haase-Pettingell C, Piret J, King JA, Chiu W. 2014. Protruding knob-like proteins violate local symmetries in an icosahedral marine virus. Nature Communications doi: 10.1038/ncomms5278.
  3. Raytcheva, DA. 2012. Life cycle, novel proteins and structural organization of the Synechococcus cyanophage Doctoral thesis, Northeastern University.
  4. Raytcheva, DA, Haase-Pettingell C, Piret JM and King JA. 2011. Intracellular assembly of cyanophage Syn5 proceeds through a scaffold-containing capsid. Journal of Virology 85: 2406-2415.
  5. Raytcheva DA, Haase-Pettingell C, Piret JM and King JA. 2014. Two novel proteins of cyanophage Syn5 compose its unusual horn structure. Journal of Virology 88(4): 2047-55.

Jon – Thank you for all the good science, good people and good parties! Thank you also for your political and social justice work which continue to inspire me. You’ve touched many people.