The P. chromatophora symbiont was related to the Prochlorococcus and Synechococcus cyanobacteria (sister to the group consisting of the living members of those two genera).
Synechococcus has been observed to occur at concentrations ranging between a few cells per ml to 106 cells per ml in virtually all regions of the oceanic euphotic zone except in samples from the McMurdo Sound and Ross Ice Shelf in Antarctica.
Using bacterial luciferase as a reporter for gene expression, studies have shown that, similar to Drosophila, mouse, and Neurospora clock models, the Synechococcus circadian clock is based on a negative feedback loop.