Citrate metabolism by resting cells of Propionibacterium freudenreichii
subsp. shermanii was investigated. In vivo13C
nuclear magnetic resonance
spectroscopy was used to study the pathway of citrate breakdown and to
probe its
utilization, non-invasively, in living cell suspensions.
[2,4-13C]citrate was metabolized
by resting cells to glutamate labelled in positions 2 and 4. In the presence
of lactate
or pyruvate, its rate of consumption was faster, but it was still converted
to
glutamate. No catabolic pathway other than the first third of a turn of
the
tricarboxylic acid cycle was used by Prop. freudenreichii subsp.
shermanii to degrade citrate.