Q.69 Microbial plastics are made from
(A) polyhydroxyalkanoates
(B) polystyrene
(C) polyurethane
(D) polyvinyl chloride

Correct Answer: (A) polyhydroxyalkanoates

Microbial plastics refer to biodegradable polymers synthesized by microorganisms, primarily bacteria, as intracellular carbon and energy storage compounds. Polyhydroxyalkanoates (PHAs) are the key example, produced by bacteria like Cupriavidus necator under nutrient-limited conditions with excess carbon sources.

Option Analysis

(A) Polyhydroxyalkanoates (PHAs): These are fully microbial in origin, consisting of hydroxy fatty acid monomers accumulated as granules in bacterial cells. Common types include polyhydroxybutyrate (PHB), a short-chain PHA made by numerous bacteria. PHAs are biodegradable, biocompatible, and serve as eco-friendly alternatives to petrochemical plastics.

(B) Polystyrene: This synthetic thermoplastic derives from styrene monomer, obtained via dehydrogenation of ethylbenzene from petroleum sources like ethylene and benzene. It is not produced by microbes and persists in environments due to poor biodegradability.

(C) Polyurethane: Formed by reacting polyisocyanates with polyols, typically from petrochemical or plant-based sources. Microbial production is not standard; it remains largely synthetic and non-biodegradable in natural settings.

(D) Polyvinyl chloride (PVC): Made from vinyl chloride monomer via polymerization processes starting from saltwater (chlorine) and petroleum (ethylene). It is a petroleum-derived, non-microbial plastic known for durability but environmental persistence.

Microbial plastics made from polyhydroxyalkanoates (PHAs) represent a sustainable breakthrough in biotechnology, directly addressing plastic pollution for CSIR NET aspirants studying microbial physiology and environmental biology. These biopolymers, produced by bacteria, offer biodegradable alternatives to synthetic plastics.

PHA Production Mechanism

Bacteria like Pseudomonas and Bacillus synthesize PHAs under stress, such as nitrogen limitation with glucose excess, storing up to 90% of cell dry weight as granules. Extraction yields films or pellets matching conventional plastic properties but fully compostable.

Why Not Other Options?

• Polystyrene: Petrochemical-derived from styrene; non-biodegradable.

• Polyurethane: Isocyanate-polyol reaction product; synthetic origin.

• PVC: Vinyl chloride polymer; persistent pollutant.

CSIR NET Relevance

This MCQ tests knowledge of microbial biopolymers in Unit 5 (Developmental Biology) or Unit 2 (Cellular Organization), emphasizing PHA’s role in green biotechnology.