Those round green structures inside what looks like an empty Spirogyra looked (at higher magnification) just like Acanthocystis.
Acanthocystis (or at least Acanthocystis turfacae) is algaivorous and takes on Chlorella endosymbionts. (reference)
There are two types of Chlorella that support “wild” Chlorellavirus replication (reference):
- those in endosymbiosis with Paramecium bursaria
- those in enodsymbiosis with Acanthocystis turfacae
I had started the Spirogyra culture for other reasons, but wouldn’t it be great if it became a feeder stock for my Chlorellavirus hosts.