Lactobacillus acidophilus reproduces by binary fission, a type of asexual reproduction.  Binary fission is when the bacterium doubles its contents and divides into two.  It is the primary form of reproduction for all bacteria, and can grow the colonies very quickly because each generation increases two fold.  This is a chart of how many bacteria would be in a colony over the course of one day, if each bacterium split every twenty minutes for an entire day.  On the y axis, it shows the numbers in scientific notation, a common way of showing large numbers.  At the end of 24 hours, there would be 4,722,366,482,869,650,000,000, or 4.7 x 10²¹ bacteria in the colony.

(Brenna Cannon)

This is a picture of a colony of L. acidophilus, and, as you can see, some of the bacteria are in the middle of binary fission.