An organism that invests energy to survive in habitats with low water activity (aw) by accumulating internal solutes to retain water is best described as:

Introduction / Context:
Water activity (aw) governs microbial water availability. Many environments—high salt, high sugar, or dry foods—impose osmotic stress. Microorganisms that withstand these conditions adjust their internal osmolarity to avoid dehydration. This item tests your vocabulary around osmotic stress adaptation.

Given Data / Assumptions:

• Habitat has low aw due to solutes (NaCl, sucrose) or dryness.
• Microbe must prevent water loss and maintain turgor.
• Cell expends energy to synthesize or import compatible solutes.

Concept / Approach:
“Osmotolerant” microbes grow over a wide aw range by accumulating compatible solutes (for example, proline, glycine betaine, trehalose) without disrupting cellular proteins. This distinguishes them from “osmophiles,” which prefer very low aw. The key is active regulation of internal solute concentrations to retain water and keep enzymes functional despite external osmotic pressure.

Step-by-Step Solution:
Identify the stress: low aw (hyperosmotic environment). Recall the strategy: compatible solute accumulation to balance osmotic pressure. Map definitions: osmotolerant aptly describes this capacity. Select “osmotolerant.”

Verification / Alternative check:
Yeasts used in sweet doughs and halotolerant staphylococci on salted foods exemplify osmotolerance, thriving where non-tolerant microbes fail.

Why Other Options Are Wrong:

• Acidophile/Alkalophile: Adapt to pH extremes, not osmotic stress.
• Aerotolerant anaerobe: Oxygen tolerance phenotype; unrelated to aw.

Common Pitfalls:
Confusing “osmotolerant” (broad tolerance) with “osmophilic” (preference for very low aw environments such as syrups and honey).

Final Answer:
osmotolerant.