Lesson 3: Microbial Nutrition

Microbial Nutrition and Growth Requirements

• Photolithotrophs: Organisms that use light and inorganic compounds for energy and carbon.
• Chemoorganotrophic heterotrophs: Organisms that obtain energy from organic compounds.

Essential Nutrients

• Nitrogen:

  • Crucial for amino acids, purines, and lipids.
  • Utilized by autotrophs and some microbes by reducing nitrate to ammonia.

• Phosphorus:

  • Present in nucleic acids, ATP, and phospholipids.
  • Required by all microbes.

• Sulfur:

  • Needed for amino acids like cysteine and methionine.
  • Some microbes need reduced sulfur forms like cysteine.

Growth Factors

• Vital for microbes lacking specific enzymatic pathways.
• Includes:
  • Amino acids: Essential for protein synthesis.
  • Purines & Pyrimidines: Required for nucleic acid synthesis.
  • Vitamins: Act as co-factors in enzymes, needed in small amounts.

Gaseous Requirements

• Aerobic Bacteria: Require oxygen for growth (e.g., Pseudomonas aeruginosa).

• Anaerobic Bacteria: Thrive in absence of oxygen (e.g., Clostridium tetani).

  • Obligate anaerobes: Die in oxygen.
  • Facultative anaerobes: Can use oxygen or grow via fermentation.

• Microaerophilic Bacteria: Prefer low oxygen concentrations.

Temperature Requirements

• Temperature affects microbial growth significantly; optimal temperatures vary.
  • Psychrophiles: Grow at 15°C or lower.
  • Psychrotrophs: Thrive at 20-30°C.
  • Mesophiles: Optimal growth between 25-40°C.
  • Thermophiles: Prefer 55-60°C.

Other Growth Requirements

• Include moisture, pH, light exposure, osmotic balance, and mechanical stress.

Culture Media Types

• Defined Media: Know exact composition; made from pure chemicals.

• Complex Media: Made from digests of biological materials like yeast and meat extracts.

• Consistency:

  • Solid Media: Typically contains 2% agar for colony observations.
  • Liquid Media: No agar, used for growing cultures.
  • Semi-solid Media: Used to examine motility.

• Nutritional Type:

  • Simple Media: Nutrient-rich for non-fastidious microorganisms.
  • Enriched Media: Contains special nutrients for fastidious microbes (e.g., blood agar).

• Functional:

  • Selective Media: Prevent growth of unwanted bacteria.
  • Differential Media: Contains indicators to reveal metabolic reactions (e.g., MacConkey agar).

Isolation of Pure Cultures

• Essential for species characterization and identification.
• Methods include:
  • Streak Culture: Isolates colonies from clinical samples.
  • Pour Plate Method: Estimates viable cell count in a sample.

Agar and Colony Morphology

• Agar solidifies media, allowing growth of colonies for study.
• Colony characteristics help identify purity and contamination levels.

Microbial Growth Phases

• Lag Phase: Metabolic activity without division.
• Log Phase: Rapid exponential growth.
• Stationary Phase: Balance between dividing and dying cells.
• Death Phase: Decline in viable cell numbers.

Growth Measurement Techniques

• Microscopic Cell Count: Direct counting under microscope.
• Viable Count: Bacteria counted post-culture on solid media.
• Turbidimetric Methods: Measures light blockage by bacterial growth in media.

Diauxic Growth

• Growth pattern when microbes metabolize two sugars sequentially.

Continuous Culture Techniques

• Chemostats maintain steady-state growth by continuous nutrient renewal.

Key Measurement Techniques

• Methods include direct microscopic counts, electronic enumeration, and various plate counting methods.

Explore the essential elements for autotrophic and heterotrophic organisms in this quiz. Topics include nitrogen, phosphorus, and sulfur along with their roles in synthesizing vital biomolecules. Test your knowledge on the biochemical needs of various microbes and their metabolic processes.