How to Use
Vector Design Studio
OD600 Calculator
Measuring the number of bacterial cells in culture without disruption of growth is a technique which can
be applied to various microbiology experiments, such as recombinant protein expression, and library construction. VectorBuilder’s OD600 calculator allows researchers to input their
OD600 measured on a
spectrophotometer and quickly convert it to an approximate count of bacterial cells.
OD600 basics
Optical density 600 (OD600) is a common method used to estimate the concentration of bacterial cultures and track growth. By measuring the absorbance of light at 600 nm as it passes through a 1 ml bacterial suspension at a path length of 1 cm, scientists can determine the turbidity of the solution, which correlates with the number of bacterial cells present. This technique is widely used because it provides a quick and easy way to monitor bacterial growth in real-time, allowing researchers to track the progress of their cultures. The higher the OD600 reading, the more cells are present in the culture, making it a tool for experiments requiring bacterial growth measurements.
Bacterial cell growth
Bacterial cells grow in distinct phases during their lifecycle: the lag phase, log (exponential) phase, and stationary phase. In the lag phase, bacteria prepare for growth by synthesizing necessary enzymes and metabolites. During this phase, cell division is minimal, and the OD600 readings remain relatively constant. The log phase follows, where bacteria rapidly divide, leading to exponential growth and in this phase, the OD600 increases logarithmically. Eventually, the culture enters the stationary phase, where nutrient depletion and waste accumulation halt growth, leading to a plateau in or stationaryOD600 readings.
Figure 1. (A) Relationship between OD600 measurement and the growth phases of bacteria. (B) Representative depiction of how bacterial cells scatter light allowing for their concentration to be determined.
OD600 calculation
OD600 measurements are used to track bacterial growth through these phases and to estimate cell concentration. When light passes through a bacterial culture, cells scatter the light, causing an increase in absorbance that can be quantified as OD600 .The concentration of cells in culture can be calculated using the equation below. However, be aware this method measures all particles, including dead cells and debris, which can skew results.
Bacterial Cells = OD600 x (8 x 108 Bacterial Cells)
Figure 2. Estimate of number of bacterial cells in culture based on the OD600 measured by a spectrophotometer.