Factors that can influence if or how microbes can grow are temperature, pH, dissolved gases, osmotic pressure and water availability. Microbes, such as bacteria are sensitive to the hydrogen ion concentration they find in their environment. Usually, the catalytic properties of the enzymes are lost and metabolism is halted. Such acid loving microbes are called acidophiles . Even though they can live in very acid environments, their internal pH is much closer to neutral values.
Some bacteria produce acid as they grow.
This acid is excreted and lowers the pH or the surrounding environment. This eventually brings bacterial growth to a halt unless something else in the environment neutralizes the bacterial acid. When grown in broth, a buffering agent can be used to mop up the excess acid, and keep the pH of the growing culture at optimum values. Each species of microbe has its own characteristic range of pH values in which it grows and reproduces best. Each growing culture is carefully buffered at the appropriate, and constant, pH for the length of the experiment.