Accumulation of Keto Acids During the Growth Cycle of Escherichia coli.

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Abstract
The accumulation of keto acids during the active growth of E. coli has been followed by a colorimetric method. The keto acids were identified by thin layer chromatography. Also the influence of a low nitrogen content and the influence of the amino-acids L-isoleucine, L-leucine, L-valine, and L-serine on the formation of keto acids in E. coli cultures were studied. Pyruvic acid accumulates during the active growth cycle in a nitrogen-rich medium so that its content rises to a miximum in the acceleration phase, decreases and then rises to a second maximum at the end of the growth cycle at which stage small amounts of 2-oxoglutaric acid are secreted into the medium. Traces of other keto acids are also produced during the growth cycle. More 2-oxoglutaric acid is formed in nitrogen-poor than in nitrogen-rich medium. Added amino-acids lead to the accumulation of the corresponding keto acids in the media already in the early phases of bacterial growth. L-Isoleucine, L-leucine, and L-valine promote the formation of the corresponding keto acids, but also the keto acids corresponding to the other two amino acids are formed in cultures containing one of these amino acids. These observations suggest that a common trans-aminase catalyzes the conversion of these amino acids.

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