Question

Exopolysaccharides are often produced by microorganisms in response to

• A. Low nutrient availability
• B. High temperatures
• C. Presence of antibiotics
• D. Sunlight exposure

Hint:

• Exopolysaccharides (EPS) are extracellular polymers, often forming capsules or slime layers.
• They play roles in adhesion, protection (against desiccation, phagocytosis, toxins, antibiotics), biofilm formation, and nutrient trapping.
• EPS production is often induced or enhanced under stress conditions, including nutrient limitation (especially when a carbon source is still abundant but other essential nutrients are scarce).

Answer 1

The Correct Option is A

Exopolysaccharides (EPS) are high-molecular-weight polymers composed of sugar residues that are secreted by microorganisms (bacteria, fungi, algae) into their surrounding environment. They form a major component of biofilms. The production of EPS is often a response to various environmental conditions, including stress:

• Nutrient Availability:
  • Low nutrient availability (Option a): Under nutrient limitation (especially when carbon is available but other nutrients like nitrogen or phosphorus are limiting), many microbes switch their metabolism towards EPS production. EPS can serve as a protective barrier, help in adhesion, or act as a reserve. This is a common trigger.
  • Excess carbon source with limitation of another nutrient often stimulates EPS production.
• Stress Conditions: EPS production can be enhanced by various environmental stresses such as osmotic stress, desiccation, presence of toxic compounds (like antibiotics - option c, or heavy metals), extreme temperatures (option b - though specific temperature ranges might be optimal for certain EPS producers, extreme high temps are usually detrimental to growth overall).
• Biofilm Formation: EPS is crucial for the formation and structural integrity of biofilms, providing a protective matrix for the microbial community. Biofilm formation itself can be triggered by surface attachment or environmental cues.
• (d) Sunlight exposure: While relevant for photosynthetic microbes, it's not a universal trigger for EPS in all EPS-producing microbes in the same way nutrient stress is.

Considering the options, "Low nutrient availability" is a well-documented and significant factor that often induces or enhances exopolysaccharide production in many microorganisms as a survival or adaptive strategy. While other stresses like presence of antibiotics or temperature extremes can also influence EPS, nutrient limitation (especially an imbalance like C-excess and N/P-limitation) is a key trigger. \[ \boxed{\text{Low nutrient availability}} \]