Clostridium tetani
Tetanus toxin, also known as tetanospasmin is a potent neurotoxin produced by "Clostridium tetani" and causes the disease state, tetanus. The LD50 of this toxin has been measured to be approximately 1 ng/kg, making it second only to botulinum toxin D as the deadliest toxin in the world. It functions very similarly to botulinum neurotoxin by attaching and endocytosing into the presynaptic nerve terminal and interfering with SNARE protein complexes. It differs from botulinum neurotoxin in a few ways, most apparently in its end state, wherein tetanospasmin demonstrates a rigid / spastic paralysis as opposed to the flaccid paralysis demonstrated with botulinum neurotoxin.