Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne pH and Bacterial Growth
Name: Amy W.
Status: Student
Age: 14
Location: N/A
Country: N/A
Date: N/A 

Can you describe in detail how pH affects bacterial growth, and what pH level allows minimum or maximum growth?

Bacteria need a physiological pH inside their cells, just like all other living organisms. Their ability to survive in extreme pH (either high or low) depends on their ability to correct for the difference between inside and out. One example of a bacterium that can live in acidic environments is Helicobacter pylori which lives in the stomach. It produces high amounts of urease which is an enzyme that degrades urea, and by doing so decreases the acidity (raises the pH). Imagine the bacteria produce a 'cloud' of neutral pH around them to protect them from the acidic environment.

There are other bacteria that are specialized to live in basic pH, for instance near black smokers, geological fountains of minerals that shoot highly alkaline minerals into the ocean. In conclusion, which pH is lethal for the bacteria depends on the species. Their defense is to keep the protons or OH- ions out. Would they not succeed, then their proteins would rapidly denature. That is the lethal toxicity of non-physiological pH.

Trudy Wassenaar

This would take about a thousand pages to give some of the details. VERY briefly, the pH affects the ionization and therefore the binding and interaction of a myriad of molecular processes...this includes very basic things such as nutrient availability. For example, depending on the pH certain metals will take on different ionization states and therefore will or will not be able to be utilized. PH also affects the solubility of many sunstances that bacteria need. There is also no certain pH level for maximum growth for bacteria in general since they all differ slightly in their evolution. Some grow in a very acid environment eg. H. pylori while others do many Pseudomonas. Species... nothing is simple in science. :)

Peter Faletra Ph.D.
Office of Science
Department of Energy

pH affects bacteria the same way it affects all living things. Extremes of pH affect the function of enzyme systems by denaturing them. However, bacteria become adapted over time to their surroundings. Just like we have enzymes that are adapted to the pH of our stomachs (very acidic) or to the small intestine (basic), bacteria that live in acid conditions are adapted to them. If they are moved to an environment that is neutral or basic they will probably die. So my point is, it depends on the bacteria and what its natural environment is. Bacteria that are human or animal pathogens are generally adapted to a pH of about 7.4 which is slightly basic.


Click here to return to the Molecular Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory