Lecture Notes: Media and Methods for Culturing Algae

Introduction

• Previous lecture covered isolation of algae from various sources.
• Today's focus: media and methods for culturing algae.

Importance of Culture Medium

• Essential for providing nutrients for algal growth.
• Design is crucial for successful growth.

Components of Culture Medium

• Primary Nutrient Sources:
  • Carbon Sources:
    • Algae are autotrophic; fix CO2 from atmosphere.
    • Can use sterilized air or CO2-enriched air.
  • Nitrogen Sources:
    • Provided in organic or inorganic form depending on algal strain.
• Minerals (added in larger quantities):
  • Phosphorus, sulfur, potassium, magnesium, iron, manganese, sodium, calcium.
• Trace Elements (added in small quantities):
  • Boron, copper, molybdenum, zinc, cobalt.
• Vitamins and Growth Factors:
  • Added in small quantities to enhance growth.

Heterotrophic Growth

• Some strains (e.g., Chlorella, Scenedesmus) can grow heterotrophically by absorbing organic carbon.

Designing Culture Medium

• No single medium suits all algal species due to structural and morphological differences.
• Stock Solution: Concentrated mixture of macronutrients, trace elements, and vitamins.

Factors Influencing Algal Growth

1. Light Source:

   • Light drives photosynthesis; intensity and spectral quality are important.
   • Higher light intensity needed for deeper culture vessels.
   • Optimal light conditions prevent photoinhibition.
     • Example: 1000 lux for small flasks, 5000-10000 lux for larger tanks.
   • Fluorescent tubes should emit blue or red light; minimum of 18 hours illumination recommended.

2. pH:

   • Freshwater algae: pH 7-9 (optimal 8.2-8.7).
   • Marine algae: alkaline conditions.
   • pH maintenance: through aeration and CO2 addition.

3. Aeration and Mixing:

   • Prevents sedimentation and ensures uniform exposure to light/nutrients.
   • Mixing methods: mechanical stirrers, paddle wheels, jet pumps.
   • Care needed for delicate algae to avoid damage.

4. Temperature:

   • Optimal range: 20-24°C (some strains tolerate up to 27°C).
   • High temperatures (>35°C) can be lethal.
   • Temperature control methods: refrigerated air conditioning, cold water flow.

5. Salinity:

   • Marine phytoplankton optimal salinity: 20-24 g/L.
   • Lower salinity than natural habitat is beneficial for growth.

6. Silica for Diatoms:

   • Continuous silica supply needed for diatom frustule formation.

Types of Culture Media

• Synthetic Media: All components known.
• Natural Water Media: Enriched with minerals or stock solutions.
• Liquid Wastes: Algae can thrive in effluents from industries.

Examples of Culture Media

• Bowles Basin Medium: Freshwater algae, pH 6.6.
• Choose Medium: For soil and freshwater algae.
• Walz Medium: Marine algae, boron omitted if using seawater.

Culturing Methods

1. Indoor vs. Outdoor Culturing:
   • Indoor: More control over conditions.
   • Outdoor: Economical but less controllable.
2. Open vs. Closed Culturing:
   • Open: Trays, ponds, tanks.
   • Closed: Tubes, flasks, bags.
3. Axenic vs. Non-axenic Cultures:
   • Axenic: Free of contaminants; expensive and difficult.
   • Non-axenic: Cheaper but inconsistent quality.

Culturing Systems

1. Batch Culturing:

   • Simple, low-cost, closed system.
   • Limited resources lead to nutrient exhaustion before harvesting.
   • Major disadvantages: low efficiency and labor-intensive for harvesting.

2. Continuous Culturing:

   • Highly efficient; maintains steady state.
   • Two types:
     • Chemostat: Maintains growth with limiting nutrients.
     • Turbidostat: Maintains predetermined cell density based on turbidity.

3. Semi-continuous Culturing:

   • Partial harvesting with immediate nutrient addition.
   • Better yield than batch but risk of metabolite build-up.

Conclusion

• Overview of media and methods for algal culturing.
• Next lectures will focus on large scale algae growth.