Log Phase

Table of Contents

| Bacterial Growth Curve | Log Phase - Overview | Frequently Asked Questions |

Bacterial Growth Curve

Bacterial growth is defined as the increase in the population of bacteria by the proliferation of one bacterium into two daughter cells. A typical bacterial growth curve shows the preparation, division, growth and death of the bacterial cells.

The growth of microbes such as bacteria, yeasts, or protozoa in batch culture can be divided into four stages:

Lag Phase

Log Phase

Stationary Phase

Death Phase

Here, let’s take a look at bacterial growth in a log phase.

Log Phase Overview

Log Phase Definition

The growth phase of a cluster of cells in a culture medium is characterized by an exponential increase in the number, which is reflected by a straight line segment when the logarithm of numbers is plotted against time on a growth curve.

Log phase, also called the exponential phase or logarithmic phase, is a phase observed in a bacterial growth curve. It is characterized by the ability of cells to double in number through binary fission. The number of new bacteria that appear each time is proportional to the current population. The generation time (the time taken for a population to double) of a bacterial species is genetically predetermined and is dependent on factors such as pH, temperature, nutrition, etc.

The relationship between the number of cells and time in the phase of exponential growth can be seen in a semi-logarithmic graph, which plots the natural log of the cell number against the factor of time. This results in a straight line, and the slope of this line is the specific growth rate of the organism, which is a quantification of the count of divisions per cell per unit time. Doubling remains constant if growth is not restricted, thus leading to an increase in the population rate over time.

However, the rate of growth in a bacterial growth curve is dependent on the conditions of growth which affect the regularity of cell division and the chances of daughter cells surviving. Cyanobacteria under favourable controlled criteria can multiply their population by fourfold every day, and even up to threefold. However, this type of growth cannot be sustained indefinitely as the environment soon becomes depleted of nutrients and filled with waste.

The log phase of bacterial growth is preferred for industrial applications and research purposes due to its constant growth rate and steady/consistent metabolic activity. Unfortunately, this is also the stage where bacteria are most susceptible to the action of antibiotics and disinfectants, which can affect cell-wall synthesis, DNA and protein.

Frequently Asked Questions

What is the Log and Lag Phase?

The Lag phase is the phase where the cells grow in size and prepare for cell division. Following this is the Log phase where the cells divide in an exponential manner.

What are the ways to extend the log phase?

The supply of nutrients can be increased to extend the log phase.

How Does Using Cells in the Log Phase Benefit Us?

Biologists prefer to use microbial culture in the log phase because at that stage the cells are the most viable.

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