Distinguish between biodegradation and biodeterioration. Write a short note on biodeterioration highlighting types, classification and implications.

1. Distinguish between Biodegradation and Bioremediation (5 marks) Biodegradation refers to the natural process by which microorganisms (bacteria, fungi, etc.) break down complex organic compounds into simpler substances like CO_2, H_2O, minerals, and biomass. Bioremediation is the deliberate application of biodegradation using microorganisms (or plants/animals) to clean up or neutralize pollutants and contaminants in the environment, such as oil spills or heavy metals in soil/water. Key differences: | Aspect | Biodegradation | Bioremediation | |--------|----------------|---------------| | Definition | Natural microbial breakdown of organics | Engineered use of microbes to remediate pollutants | | Scope | Any organic matter degradation | Targeted environmental cleanup | | Purpose | Part of nutrient cycling | Pollution control/restoration | | Control | Spontaneous | Engineered (bioaugmentation/biostimulation) | | Examples | Decay of leaves | Oil spill cleanup using bacteria | 2. Write short notes on: (i) Biofilm formation (3 marks) Biofilm formation is a multi-step process where microorganisms adhere to surfaces and develop structured communities embedded in a self-produced matrix of extracellular polymeric substances (EPS). Steps: Initial attachment: Reversible adhesion via weak forces (van der Waals, hydrophobic interactions). Irreversible attachment: Firm binding via pili, fimbriae, adhesins. Microcolony formation: EPS production (polysaccharides, proteins, DNA). Maturation: Mushroom-like 3D structure with channels for nutrient flow. Dispersion: Cells release to colonize new sites. Biofilms protect microbes from antibiotics, enhance resistance (e.g., dental plaque, medical device infections). (ii) Quorum sensing (2 marks) Quorum sensing (QS) is cell-to-cell communication in bacteria via autoinducer signaling molecules (e.g., acyl-homoserine lactones in Gram-negatives). Process: Low density: Low autoinducer. High density: Autoinducer threshold reached → gene expression (bioluminescence, virulence, biofilm). Examples: Vibrio fischeri (light), Pseudomonas aeruginosa (pathogenicity). Regulates population-dependent behaviors. 3. List and describe major compositional factors that influence biodegradation (2.5 marks) Major factors: Chemical structure: Straight-chain alkanes degrade faster than branched/aromatic; position of functional groups matters. Molecular weight: Low MW polymers degrade easier than high MW. Solubility/Hydrophobicity: Hydrophilic > hydrophobic (better microbial access). Functional groups: Presence of OH, COOH enhances via co-metabolism. Inhibitors: Halogens, heavy metals slow degradation. 4. Write short note on the mechanism by which metal ions regulate the oxidation of hydrocarbons and how they can [likely "inhibit/promote"] (5 marks) (Note: Assuming full question based on snippet "Write short note on the mechanism by which metal ions regulate the oxidation of hydrocarbons and how they can") Metal ions (e.g., Fe^2+, Mn^2+, Co^2+) act as cofactors in mono/dioxygenase enzymes for hydrocarbon oxidation. Mechanism: Activation: Fe^2+ in alkane hydroxylases (e.g., rubredoxin) facilitates O_2 insertion into C-H bonds. Electron transfer: Ions shuttle electrons in redox reactions. Cometabolism: Metals induce enzymes for co-substrates. Promotion: Essential for dioxygenases in aromatics (e.g., catechol dioxygenase). Inhibition: Excess Hg^2+, Cd^2+ denature enzymes, compete sites, generate ROS. 5. List types of synthetic biodegradable plastics and one microbial genus capable of their degradation (8.5 marks) Types of synthetic biodegradable plastics: Polylactic acid (PLA): From lactic acid; used in packaging. Degraded by Amycolatopsis sp. Polyhydroxyalkanoates (PHA): Bacterial polyesters (PHB, PHBV); films/bottles. Degraded by Pseudomonas sp. Polycaprolactone (PCL): Low MW polyester; drug delivery. Degraded by Bacillus sp. Polybutylene succinate (PBS): Aliphatic polyester; bags. Degraded by Rhodococcus sp. Polybutylene adipate terephthalate (PBAT): Flexible; mulch films. Degraded by Clostridium sp. Each has microbes producing extracellular depolymerases under aerobic/anaerobic conditions. 6. Using well labelled diagram, explain the mechanism of plastic biodegradation under aerobic conditions (17.5 marks) Mechanism of aerobic plastic biodegradation: Plastics (e.g., PE, PET, PU) are xenobiotics; microbes use them via extracellular/intracellular enzymes. Steps: Step 1: Biodeterioration - Surface colonization by microbes (biofilm), physical cracking via acids/enzymes. Step 2: Biofragmentation - Extracellular enzymes (e.g., PETase, MHETase for PET; laccases, peroxidases for PU/PE): End-chain attack → oligomers. Random scission → smaller fragments. Step 3: Bioassimilation - Oligomers transported via ABC transporters; intracellular oxidation: Alcohol/aldehyde dehydrogenases → carboxylic acids. -oxidation pathway → acetyl-CoA. Step 4: Mineralization - TCA cycle → CO_2, H_2O, biomass. Key enzymes (example for PET): PETase: PET → MHET + TPA. MHETase: MHET → TPA + EG. TPA/EG → central metabolism. Factors: O_2, neutral pH, 30-50°C optimal. Diagram (schematic pathway): &Plastic polymer (e.g., PET) \\ & (PETase, cutinase) \\ &Oligomers (MHET, TPA) \\ & (transporters) \\ &Intracellular: -oxidation Acetyl-CoA \\ & (TCA cycle) \\ &CO_2 + H_2O + biomass Microbes: Ideonella sakaiensis (PET), Pseudomonas (PE/PHA), Aspergillus (fungi for PU). **Final summary: Aerobic pathway ensures complete mineralization with O_2 as terminal electron acceptor.