pH optimum for bacterial growth

Dave Boone boone at
Tue Aug 15 11:27:47 EST 1995

>Good  buffers are a good choice only if the bacteria do not degrade them.
>They are a bad choice, in my opinion, for enrichment cultures, since you may
>enrich for buffer degraders.  Sodium bicarbonate and sodium carbonate, are a
>better choice.  The carbon dioxide buffer system is more ecologically
>correct than most other buffers.

I agree: bicarbonate buffers are usually the most "natural" choice. 
However, if you cannot maintain a substantial CO2 partial pressure in the
gas that is in equilibrium with the medium, this system will only work at
pH values higher than 8.  I have used CO2/bicarbonate/carbonate buffers
for years in anaerobic cultures, where the gas phase is controlled
in sealed vessels anyway.  Modifying pH (between, say, 6.5 and 7.5) often
requires only changing the partial pressure of CO2 in the gas.  More
alkaline pH values can be obtained by adding NaOH, but at high pH values
calcium carbonate or other carbonates may form.

dave boone
David R. Boone                  | "Many scientists classify bacteria.  Which
Prof. of Environ. Microbiology  | means that it is only for them to know, and
Oregon Graduate Institute       | they won't tell other people about it."
503-690-1146, fax 503-690-1273  |        --from a 4th-grade science project
boone at;

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