Bacterial Growth and Culture Techniques

Understanding how bacteria grow, divide, and respond to their environment is fundamental to microbiology. This lesson covers the bacterial growth curve, methods of culturing bacteria, and the use of culture media, as required by the Edexcel A-Level Biology (9BI0) specification.

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Binary Fission

Bacteria reproduce asexually by binary fission — a single cell divides into two identical daughter cells.

Steps of Binary Fission

1. The circular DNA molecule replicates — each copy attaches to the cell membrane at different points.
2. The cell elongates and the two DNA copies move apart.
3. The cell membrane invaginates (grows inward) at the centre of the cell.
4. A new cell wall forms across the centre, creating a septum.
5. The cell divides into two identical daughter cells, each with a copy of the chromosome.

Generation Time

The generation time (doubling time) varies between species and depends on conditions:

Organism	Approximate generation time
Escherichia coli (optimal conditions)	~20 minutes
Mycobacterium tuberculosis	~15–20 hours
Staphylococcus aureus	~30 minutes