An organism that has peroxidase and superoxide dismutase but lacks catalase is most likely an
a. aerobe.
b. aerotolerant anaerobe.
c. obligate anaerobe.

Verified step by step guidance

1. Understand the role of the enzymes: Peroxidase, superoxide dismutase, and catalase are enzymes that help organisms manage reactive oxygen species (ROS).
2. Peroxidase and superoxide dismutase help in breaking down harmful oxygen derivatives, allowing some organisms to tolerate oxygen.
3. Catalase breaks down hydrogen peroxide into water and oxygen, providing protection against oxidative damage.
4. An organism with peroxidase and superoxide dismutase can tolerate oxygen but may not use it for growth, indicating it is not an obligate anaerobe.
5. Consider the characteristics of aerotolerant anaerobes: They can survive in the presence of oxygen due to these enzymes but do not use oxygen for metabolism, unlike aerobes.

Key Concepts

Reactive Oxygen Species (ROS)

Reactive oxygen species are highly reactive molecules that can damage cellular components. Organisms produce ROS as byproducts of aerobic metabolism, necessitating protective enzymes like superoxide dismutase and catalase to mitigate oxidative stress. Understanding ROS is crucial for determining how different organisms cope with oxygen.

Enzymatic Defense Mechanisms

Enzymatic defense mechanisms, such as peroxidase, superoxide dismutase, and catalase, are critical for organisms that encounter oxygen. Peroxidase and superoxide dismutase help neutralize harmful ROS, while catalase specifically breaks down hydrogen peroxide. The presence or absence of these enzymes informs us about an organism's oxygen tolerance and metabolic capabilities.

Oxygen Tolerance Categories

Microorganisms are categorized based on their oxygen tolerance: aerobes require oxygen, anaerobes cannot tolerate it, and facultative anaerobes can grow with or without oxygen. Aerotolerant anaerobes can survive in oxygen but do not use it for growth. Identifying the type of organism based on its enzymatic profile helps classify its oxygen tolerance.