A team of international scientists have shown that it's possible to harvest very tiny amounts electrical current from algae:
The amount of current harvested from the algae is tiny — far too little to power any consumer electrical device. To get even one amp, the scientists would have to hook up trillions of cells, said Prinz.
That would take far too long, since the process reduces the algae's lifespan down to tens of minutes. Furthermore, the amount of current harvested does not exceed the amount of current necessary to jump start the algae into producing energy; there was no net gain in energy from the experiment.