Life Cycle of Micro-organisms

Introduction

• Micro-organisms can rapidly multiply under suitable conditions, leading to exponential growth.
• Growth is characterised by four main phases: Lag, Log (Exponential), Stationary, and Death Phase.

Lag Phase

• Little to no increase in microbe numbers, but metabolic activity is high.
• Microbes adjust to growth media conditions, and enzymes are induced for substrate metabolism.

Log (Exponential) Phase

• Microbes multiply at a constant rate, representing the most rapid growth.
• Requires a constant supply of nutrients and appropriate environmental conditions (e.g., temperature, pH, O2 levels).

Stationary Phase

• Growth medium depleted of nutrients; toxic metabolites accumulate, leading to increased pH.
• Secondary metabolites are produced, which are not essential for survival but can provide ecological advantages.
• Antibiotics are an example of secondary metabolites that can outcompete other micro-organisms.
• Microbe production equals microbe death, resulting in no net growth.

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Life Cycle of Micro-organisms

Death Phase

• Microbes die due to the lack of nutrients and the build-up of toxic metabolites.
• Viable cell count includes living micro-organisms, while total cell count includes both viable and dead cells.
• Only viable cell counts show a death phase where cell numbers decrease.

Growth Curve Analysis

• Semi-logarithmic scales are used for growth curve analysis due to the wide range of data on the y-axis.