The utilisation of D-galactonate and D-2-oxo-3-deoxygalactonate by Escherichia coli K-12. Biochemical and genetical studies

Cooper, R.A.

Archives of Microbiology 118(2): 199-206


ISSN/ISBN: 0302-8933
PMID: 211976
DOI: 10.1007/bf00415730
Accession: 068524248

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E. coli K-12 mutants unable to grow on D-galactonate were isolated and were defective in either galactonate dehydratase, 2-oxo-3-deoxygalactonate 6-phosphate aldolase or devoid of both of these enzymes and of 2-oxo-3-deoxygalactonate kinase. 2-Oxo-3-deoxygalactonate kinase and 2-oxo-3-deoxygalactonate 6-phosphate aldolase are still induced by galactonate in mutants lacking galactonate dehydratase, suggesting that galactonate rather than a catabolic product of galactonate is the inducer of the galactonate catabolic enzymes. Synthesis of the enzymes is subject to glucose catabolite repression. Mutants defective in 2-oxo-3-deoxygalactonate 6-phosphate aldolase accumulate 2-oxo-3-deoxygalactonate 6-phosphate when exposed to galactonate and this compound causes general growth inhibition. Secondary mutants that no longer show this inhibition fail to make 2-oxo-3-deoxygalactonate 6-phosphate due to additional defects in galactonate transport, galactonate dehydratase, 2-oxo-3-deoxygalactonate kinase or a putative promoter mutation that prevents formation of these enzymes. A spontaneous mutant capable of growth on 2-oxo-3-deoxygalactonate was isolated. It has 2 genetically distinct mutations. One permits constitutive formation of the galactonate catabolic enzymes and the other allows the uptake of 2-oxo-3-deoxygalactonate. Neither mutation on its own permitted growth on 2-oxo-3-deoxygalactonate. Genes specifying the various galactonate catabolic enzymes were located at min 81.7 on the E. coli K-12 linkage map and probably constitute an operon. The gene sequence in this region was pyrE uhp dgo dnaA.