Lagfase

Lagphase, in microbiology, is the initial phase of growth after inoculation of a culture into fresh medium. During this period there is little or no net increase in biomass as cells acclimate to the new environment. Metabolic activities ramp up: cells synthesize new enzymes, transport systems, and ribosomes, repair damage, and adjust to available nutrients before entering rapid division.

The duration of the lag phase varies widely. It depends on the organism, the physiological state of the inoculum, the nutrient composition and temperature of the medium, pH, oxygen availability, and prior stress exposure. A fresh, compatible environment or a culture taken from a similar condition tends to yield a short lag, while hostile conditions, strong nutrient shifts, or transfer from stationary phase can prolong it.

Lag phase is followed by the exponential (log) phase, in which cells divide at a constant, rapid rate. In some cases, the lag time is measurable and significant for planning experiments or industrial processes. It is often quantified from growth curves by measuring optical density or viable cell counts and identifying the onset of exponential growth.

In modeling growth curves, lag time is a key parameter (as in Baranyi and Gompertz models). Understanding the lag phase is important for fermentation design, food safety, and microbiological experimentation, because it influences timing of product formation, contamination risk, and the interpretation of growth dynamics.