MICROBIOLOGY Study Guide - 2012

CHAPTER 8. MICROBIAL GROWTH

8.2. PARAMETERS OF THE GROWTH CURVE

Bacteria most commonly reproduce by binary fission, which causes their population to increase in a geometric progression:

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If a batch culture contains X₀ Cells per unit volume, then after n divisions the number of cells will be:

Taking the logarithm, we obtain the expression:

from which we find n:

The number of Cell divisions per hour, or the division rate constant (v), is determined from the formula:

Specific growth rate characterizes the increase in a unit of biomass per unit of time relative to the total biomass.

During the exponential growth phase, the specific growth rate (μ) is determined According to the equation:

Integrating expression [8.5], we obtain the equation:

After taking the logarithm of expression [8.6], we have:

Growth that follows this equation is referred to as exponential or logarithmic.

An important indicator of culture reproduction is the generation time (g), which is the time required for a single division cycle. Generation time is determined by the formula:

The relationship between the specific growth rate and the generation time can be established from equations 8.3 and 8.7:

The yield is defined as the difference between the maximum cell mass (biomass) achieved in the culture upon reaching the stationary phase and the biomass introduced into the medium with the inoculum:

The economic growth coefficient is expressed as The ratio of The Cell yield (X) to The amount of substrate consumed (S). Expressing both values in weight units gives:

The amount of consumed substrate is determined as the difference between the initial (S₀) and residual (S₁) substrate concentrations:

The economic growth coefficient characterizes the efficiency of substrate utilization or culture productivity under specific environmental conditions.