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

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).

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: