Final answer:
Gas gangrene is caused by the bacterium Clostridium perfringens, and the reservoir for this infection is necrotic tissue in the body.
Step-by-step explanation:
Gas gangrene is caused by the bacterium Clostridium perfringens, which is an endospore-forming, gram-positive bacterium. It is an obligate anaerobe that grows in tissue devoid of oxygen. The infection starts in necrotic tissue (dead tissue) that is not supplied with oxygen by blood circulation. Therefore, the reservoir for gas gangrene is necrotic tissue in the body.