A culture broth tube shows heavy turbidity at the bottom but remains clear at the top near the air–liquid interface. What practical conclusion about handling and incubation follows from this oxygen-dependent growth pattern?

Introduction / Context:
Growth patterns in static broth reflect oxygen gradients and help identify aerobic classes. Turbidity confined to the bottom suggests intolerance of oxygen and preference for reduced conditions, typical of obligate anaerobes.

Given Data / Assumptions:

• Top of the tube is oxygenated; the bottom is relatively anoxic.
• Growth occurs mainly where oxygen tension is lowest.
• Observation is reproducible and not due to precipitates.
• No shaking or gas sparging is performed.

Concept / Approach:
Obligate anaerobes lack sufficient reactive oxygen species defenses (for example, catalase, superoxide dismutase) and thus avoid oxygen-rich zones. The most actionable conclusion for cultivation is to provide oxygen-free handling and incubation—commonly in an anaerobic chamber or jar with appropriate gas packs and pre-reduced media.

Step-by-Step Solution:
Interpret bottom growth as oxygen-sensitive metabolism. Infer limited ROS-detoxifying capacity. Translate physiology into practice: exclude oxygen during culture. Choose “organism should be grown in an anaerobic chamber.”

Verification / Alternative check:
Thioglycollate deep-culture tests show obligate anaerobes concentrated at depth; shifting to an anaerobic chamber improves recovery and growth rates.

Why Other Options Are Wrong:

• Broth is sterile: Contradicted by visible turbidity at the bottom.
• Organism can tolerate oxygen: Opposite of the observed pattern.
• Lack of SOD/catalase (option c): Biologically plausible but less directly actionable than the required cultivation step; the question asks for the practical conclusion.

Common Pitfalls:
Confusing sedimented cells with true growth localization; verify by gentle resuspension and re-incubation or by using reducing indicator dyes (for example, resazurin) to visualize oxygen gradients.

Final Answer:
organism should be grown in an anaerobic chamber.