Bacterial Growth, Culture, and Nutritional Types
Bacterial Culture and Growth
- Synchronous culture: Culture in which all bacteria divide at the same time.
- Continuous culture: Cultures of bacteria that are maintained indefinitely in the log phase.
Phases of Bacterial Growth
The normal cycle of growth in bacterial culture includes four phases:
- Lag Phase: No significant population change; cells are metabolically active, increasing in size and adapting to the medium.
- Log Phase: Cells duplicate at regular intervals, showing uniformity in metabolic activity. This phase continues as long as conditions are favorable.
- Stationary Phase: Due to unfavorable conditions, there is a balance between new and dead cells.
- Decline Phase (Death Phase): More cells die than are produced due to nutrient depletion and toxin accumulation.
Microbial Growth Definition
In microbiology, growth refers to an increase in the number of cells, not cell size.
Bacterial Media Types
Bacterial media include:
- Synthetic or chemically defined media
- Enriched media
- Selective media
- Differential media
- Media for microbiological assays
- Media for counting bacteria
- Maintenance or storage media
- Identification media
Nutritional Requirements
Nitrogen Sources:
- N2
- Inorganic nitrogen compounds
- Organic nitrogenous compounds
Major Nutritional Types
| Group | Energy Source | Carbon Source |
|---|---|---|
| Photoautotrophic | Light | CO2 |
| Photoheterotrophic | Light | Organic Compounds |
| Chemoautotrophs | Inorganic Compounds | CO2 |
| Chemoheterotrophs | Organic Compounds | Organic Compounds |
Temperature Requirements
- Psychrophilic Bacteria: Optimal range 15-20 °C
- Mesophilic Bacteria: Optimal range 25-40 °C
- Thermophilic Bacteria: Optimal range 45-60 °C (Optional 40-45 °C, True > 60 °C)
Bacterial Reproduction
Bacteria reproduce asexually, primarily through:
- Single or binary division (transverse binary fission or splitting)
Other methods include:
- Fragmentation
- Sporulation
- Budding
Simple Binary Division Process
- Parental cell prepares for division, entering intense biosynthetic activity.
- Cell elongates, accumulating substances and duplicating the chromosome.
- Genetic material is distributed, and the cell wall invaginates.
- New cell wall is synthesized, cytoplasmic material is distributed, and two cells separate.
Bacterial Genetics
Bacteria are useful for genetic studies because:
- They share similar genetic systems with microorganisms and animals.
- They produce large populations.
- They are easy to manipulate experimentally.
- Genotype: The genetic constitution of an individual (the genes it possesses).
- Phenotype: The expressed manifestation of the genotype.
Optimal pH Conditions
To achieve optimal pH for bacterial growth:
- Maintain a pH between 6.5 and 7.5.
- Add buffers to the culture to maintain the optimum pH.