Q.44 Which of the following are true about bacterial superoxide dismutase?
P. Present in obligate aerobes
Q. Present in facultative anaerobes
R. Present in aerotolerant anaerobes
S. Absent in obligate aerobes
(A) P and Q only (B) P, Q and R only
(C) P and R only (D) Q and S only
Bacterial Superoxide Dismutase in Aerobes and Anaerobes
Bacterial superoxide dismutase (SOD) neutralizes superoxide radicals produced during oxygen metabolism, protecting cells from oxidative damage. The correct answer to this multiple-choice question is (B) P, Q, and R only, as SOD is present in obligate aerobes, facultative anaerobes, and aerotolerant anaerobes.
Correct Answer
(B) P, Q and R only
SOD is absent in strict (obligate) anaerobes but present in organisms exposed to oxygen, enabling survival by detoxifying O₂⁻ to H₂O₂ and O₂.
Option Breakdown
| Option | Statement | True/False | Explanation |
|---|---|---|---|
| P | Present in obligate aerobes | True | Obligate aerobes rely on SOD and catalase for aerobic respiration, as they constantly produce superoxide via cytochrome systems. |
| Q | Present in facultative anaerobes | True | Facultative anaerobes like E. coli switch between aerobic and anaerobic metabolism, inducing SOD under oxygen exposure for protection. |
| R | Present in aerotolerant anaerobes | True | Aerotolerant anaerobes (e.g., Streptococcus) lack cytochromes but tolerate air via SOD, metabolizing limited oxygen without catalase. |
| S | Absent in obligate aerobes | False | Contradicts P; obligate aerobes require SOD for survival in oxygen-rich environments. |
Why SOD Distribution Matters
SOD presence correlates with oxygen tolerance: strict anaerobes avoid it to prevent toxicity, while aerobes and aerotolerants use it as a first-line defense against reactive oxygen species (ROS). This pattern supports the enzyme’s role in aerobic adaptation, as shown in classic studies on microbial oxygen sensitivity. Facultative types regulate SOD levels dynamically.
