the most deadly bacteria poison-botulism. but it is also a toxin that is used to treat spasmodic torticalis, stuttering, multiple sclerosis, and cerebral palsy. 😆
And help some women in their fight against wrinkles.
Yes the botulic toxin is the most potent natural toxin, the tetanus toxin is not far behind in terms of LD50.
This pose the question of the meaning of "most deadly bacteria". The bacteria that can kill you with the best certainty, then Clostridium botulinum is a good bet. If it is in terms of body count, the black plague caused (as far as we can figure out) by Yersinia pestis would be another noteworthy candidate. But even the usually commensal Escherichia coli is still doing well and very quietly, causing in the poorest countries tens of thousands of death by diarrhea each year.
For Victor, the race probably runs between the flu virus (1918), and HIV, and I would probably bet on the last one, in terms of body count.