Why do bacteria and fungi grow more slowly in a medium with a pH higher or lower than their community?

Bacteria and Fungi populations have adapted their genetics, over the evolutionary course of many generations, to accommodate an environment with very specific resources, including pH.





If you would, for instance, streak a colony of E. coli bacteria growing in a medium with a stable pH and then grow them in nutrient agar with a lower pH, the bacterial cells would either need to upregulate and/or activate genes that code for proteins that, in-turn, help limit the affects of the lower pH (such as H+ pumps), or they would die.





This fine tuning of an organism's genome occurs over the course of a few generations, and in acclimating to the pH of the new environment, their rate of growth will slow compared to an environment with an ideal pH.