![]() The 600-nm wavelength is specifically chosen for bacterial OD measurements because unlike UV wavelengths, 600 nm is not harmful to the culture. Optical density measures the degree of light scattering caused by the bacteria within a culture the more bacteria there are, the more the light is scattered. Measuring the OD600, or the optical density (OD) at 600 nm, is the easiest way to gauge the bacterial culture growth stage. Using OD 600 Measurements to Determine Your Bacterial Culture Growth Stage If you’re working with spore-forming bacteria, this may be the stage where vegetative cells sporulate or form new spores.Īnd finally, the death (or decline) phase occurs due to a variety of factors, including a lack of nutrition or oxygen, a change in media pH as a result of cell metabolism, or an accumulation of toxic cellular waste.įigure 1. When a maximum cell density in a liquid culture is reached, cells enter the stationary phase.ĭuring this phase, there is no overall increase in the cell population-cells that die are replaced by newly dividing ones, but the overall number of live cells stays the same. Growth during this phase is exponential and metabolic activity is uniform across cells bacteria in this phase are also most susceptible to antibiotics, for example, making it the ideal phase for research work. coli can double every 20 minutes in log phase). The bacterial culture then enters the log phase, where cells rapidly divide (normally by binary fission) and double in number over a given period of time (e.g. During this time, cells are adapting and adjusting to their new environment. Let’s start by reviewing the four basic phases of a bacterial growth curve (Figure 1):Ī fresh inoculation of bacteria into culture medium starts out in the lag phase, where cells are metabolically active but not dividing. We’ll talk you through the bacterial growth curve and show you how to check what stage your culture is in using OD 600 measurements. ![]() This article is for anyone who has ever wondered, “How do I know when my bacterial culture is ‘done’ growing? When should I harvest my cells?”. ![]()
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