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J. Bacteriol., Jan 1997, 194-201, Vol 179, No. 1
LS Green and DW Emerich
The sucA gene, encoding the E1 component of alpha-ketoglutarate
dehydrogenase, was cloned from Bradyrhizobium japonicum USDA110, and its
nucleotide sequence was determined. The gene shows a codon usage bias
typical of non-nif and non-fix genes from this bacterium, with 89.1% of the
codons being G or C in the third position. A mutant strain of B. japonicum,
LSG184, was constructed with the sucA gene interrupted by a kanamycin
resistance marker. LSG184 is devoid of alpha- ketoglutarate dehydrogenase
activity, indicating that there is only one copy of sucA in B. japonicum
and that it is completely inactivated in the mutant. Batch culture
experiments on minimal medium revealed that LSG184 grows well on a variety
of carbon substrates, including arabinose, malate, succinate,
beta-hydroxybutyrate, glycerol, formate, and galactose. The sucA mutant is
not a succinate auxotroph but has a reduced ability to use glutamate as a
carbon or nitrogen source and an increased sensitivity to growth inhibition
by acetate, relative to the parental strain. Because LSG184 grows well on
malate or succinate as its sole carbon source, we conclude that B.
japonicum, unlike most other bacteria, does not require an intact
tricarboxylic acid (TCA) cycle to meet its energy needs when growing on the
four-carbon TCA cycle intermediates. Our data support the idea that B.
japonicum has alternate energy-yielding pathways that could potentially
compensate for inhibition of alpha-ketoglutarate dehydrogenase during
symbiotic nitrogen fixation under oxygen-limiting conditions.
Copyright © 1997, American Society for Microbiology
Bradyrhizobium japonicum does not require alpha-ketoglutarate dehydrogenase for growth on succinate or malate
Department of Biochemistry and Interdisciplinary Plant Group, University of Missouri, Columbia 65211, USA. bclgreen@muccmail.missouri.edu
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