Halobacteria (Cyanobacteria's dark alter ego)
Halobacteria WOULD exist without Cyanobacteria!
Despite their name, Halobacteria are not even bacteria, but actually belong to the domain Archaea, just like humans do! In fact, all eukaryotes actually belong to the domain Archaea, however, not all Archaea are eukaryotic (Halobacteria are prokaryotes). Regardless, Halo-not-bacteria would be able to exist without Cyanobacteria. Although it is true that Halobacteria prefer to live in an aerobic (has O2) environment, they can survive perfectly fine in an anerobic (doesn't have O2) one.
In fact, Halobacteria are some of the only organisms which are not related to (or do not contain, in plants' case) Cyanobacteria that can photosynthesize! They do not use CO2 in their photosynthesis process because it does not create sugars when it photosynthesizes. Instead, Halobacteria only use the process to generate ATP (kind of like if a plant were to just stop photosynthesis after the PSII part was over), and instead get organic molecules from their environment to use for energy. However, Halobacteria can also produce energy in other ways, such as fermentation. Either way, they don't rely on Cyanobacteria!
