Oxygen niches — Microaerophilic bacteria are organisms that require…

Introduction / Context:
Microaerophiles occupy a distinct ecological niche between obligate aerobes and anaerobes. They thrive where oxygen is present but at concentrations lower than atmospheric levels. This has implications for culturing pathogens like Campylobacter or Helicobacter and for understanding oxygen gradients in biofilms and natural habitats.

Given Data / Assumptions:

• Atmospheric oxygen is approximately 21%.
• Microaerophiles prefer reduced oxygen, often coupled with elevated CO2.
• We contrast exact oxygen needs versus vague enzyme activation statements.

Concept / Approach:
Microaerophiles possess respiratory chains adapted to low oxygen tensions and may be sensitive to oxidative stress at higher partial pressures. Culturing commonly uses gas mixtures with about 2–10% O2 and 5–10% CO2. This requirement distinguishes them from obligate aerobes (need ~21% O2), facultatives (broad tolerance), and anaerobes (damaged by O2).

Step-by-Step Solution:

Verification / Alternative check:
Clinical labs incubate microaerophiles in microaerophilic jars or specialized incubators with controlled gas mixes, confirming their reduced O2 requirement.

Why Other Options Are Wrong:

• 21% O2: matches obligate aerobes, not microaerophiles.
• O2 for enzyme activation: too vague; many aerobes need O2, but microaerophily is about reduced concentration.
• None of the above: incorrect since a correct definition is given.

Common Pitfalls:
Assuming microaerophiles grow better as O2 increases; in fact, high O2 can be inhibitory or lethal.

Final Answer:
low levels of oxygen for growth (lesser than O2 present in atmosphere)