List three (3) types of synthetic biodegradable plastics and one (1) microorganism capable of their degradation. List 3 types of natural plastics and one (1) microorganism capable of their degradation.

Section A

1a. Distinguish clearly between biodegradation and biodeterioration (5 marks)

Biodegradation is the microbial breakdown of organic compounds into simpler substances like CO$_2$, H$_2$O, and biomass, which is a natural, beneficial process for recycling nutrients and managing waste.

Biodeterioration is the unwanted microbial degradation of industrial materials (organic or inorganic), causing physical, chemical, or aesthetic damage leading to economic loss.

| Aspect | Biodegradation | Biodeterioration | |--------|----------------|------------------| | Nature | Beneficial, natural | Detrimental, unwanted | | Target | Organic waste | Materials like food, metals, concrete | | Outcome | Environmental recycling | Economic loss, spoilage |

1b(i). Classification of biodeterioration (2.5 marks)

Biodeterioration is classified by:

• Material affected: Food (e.g., mold on bread), textiles (rot), metals (corrosion), wood (decay), concrete (cracking), fuels (sludge).

• Microbial agents: Bacteria (e.g., sulfate-reducing), fungi (e.g., Aspergillus), actinomycetes, algae, protozoa.

1b(ii). Cost of biodeterioration (2.5 marks)

Costs include:

• Direct economic loss: $100-200 billion annually worldwide (e.g., food spoilage ~20-30% of production).

• Maintenance/repair: Corrosion costs ~3-5% of GDP in developed countries (pipelines, ships).

• Health risks: Mycotoxins in spoiled food.

2. State how 3 microbes colonize concrete (5 marks)

Concrete colonization involves adhesion, biofilm formation, acid production, and penetration.

Step 1: Thiobacillus thiooxidans (sulfur-oxidizing bacterium)
Adheres to moist surface $\rightarrow$ oxidizes S to H$_2$SO$_4$ $\rightarrow$ etches CaCO$_3$ in cement.

Step 2: Fusarium oxysporum (fungus)
Spores germinate on surface $\rightarrow$ hyphae penetrate pores $\rightarrow$ secrete organic acids.

Step 3: Oscillatoria sp. (cyanobacterium/alga)
Photosynthesizes on surface $\rightarrow$ traps moisture/dust $\rightarrow$ produces acids, physical expansion.

Section B (partial from query)

Mechanisms of microbial corrosion of metals (7.5 marks)

Microbial corrosion (MIC) involves:

Step 1: Acid production
Microbes (e.g., Thiobacillus) produce H$^+$ or organic acids, lowering pH:
$\ce{M + 2H^+ -> M^{2+} + H2}$

Step 2: Cathodic depolarization
Sulfate-reducing bacteria (Desulfovibrio) consume H$_2$:
$\ce{SO4^{2-} + 4H2 -> S^{2-} + 4H2O}$

Step 3: Biofilm effects
Anaerobic zones under biofilm $\rightarrow$ differential aeration cells.

Step 4: EPS production
Exopolysaccharides trap corrosive agents, concentrate ions.

Step 5: Enzymatic attack
Proteases/enzymes degrade passive oxide layers.

6 characteristics of biodeteriogens influencing activity:

1. Enzyme production: Cellulases, ligninases for substrate attack.

2. Adhesion capability: Pili, fimbriae, hydrophobins for surface attachment.

3. Metabolic versatility: Aerobic/anaerobic, use diverse C/N sources.

4. Acid/alkali tolerance: Thrive at pH 2-10.

5. Biofilm formation: Protects from biocides, concentrates nutrients.

6. Spore-forming: Resistant dormant stage for colonization.

Section C

5a. List 3 types of synthetic biodegradable plastics and 1 microorganism capable (4 marks)

1. Polylactic acid (PLA): From corn starch.

2. Polyhydroxyalkanoates (PHA): Bacterial polyester.

3. Polycaprolactone (PCL): Semi-crystalline polyester.

Microorganism: Amycolatopsis orientalis degrades PLA via hydrolases.

5b. Natural plastics and 1 microorganism (4.5 marks)

Natural plastics: Cellulose, chitin, natural rubber (polyisoprene).

Microorganism: Streptomyces coelicolor degrades natural rubber via latex-clearing protein (Lcp).

Final answers bolded above.