Bacillus used to test the efficacy of Sterilization by Autoclave is?
Various bacilli are used to check the efficacy of sterilization methods are:

Autoclave- Bacillus stearothermophilus
Hot air oven- Bacillus subtilis subspecies niger
Ionising radiation- Bacillus pumilus
Bacillus subtilis.
Bacillus pumilus
Bacillus stearothermophilus
Coxiella burnetii