Could cyanobacteria thrive with very high CO2 concentrations and almost no oxygen to start with?
I like this exobacteria theory question because they implement a strategy for answers that may go against or for the idea of out of space terraforming. Simply providing detail won't be enough in this case. Cyanobacteria are not very durable in Venus atmosphere. The temperature of Venus is of much higher average and they will be feeding of the atmospheric pollution as well causing an oxidative affect on the cell when too much co2 gives off oxides. But more importantly hydrogen buildup in the protein folds could cause inhibitory stress (prevents binary fission). So no I would not use Cyanobacteria as a space project. But please go against me if I'm false.