Exploitation of the broad specificity of the membrane-bound isoenzyme of lactate dehydrogenase for direct selection of null mutants in Neisseria gonorrhoeae.
Lactic acid is readily utilized as a carbon and energy source by Neisseria gonorrhoeae. The oxidation of lactate is coupled to electron transport via a membrane-bound lactate dehydrogenase (iLDH) which is independent of pyridine nucleotide. The broad substrate specificity of iLDH endows N. gonorrhoeae with the novel ability to convert phenyllactate to L-phenylalanine via phenylpyruvate. N. gonorrhoeae ATCC 27628 typifies a class of clinical isolate whose growth is inhibited by phenylpyruvate (or L-phenylalanine). Exploiting resistance to growth inhibition by phenyllactate as a strategy of positive selection, mutant derivatives of strain ATCC 27628 lacking iLDH activity were readily obtained. These mutants are incapable of oxidizing phenyllactate, and lack the parent-strain ability to reduce c-type cytochromes in the presence of lactate, phenyllactate or 4-hydroxyphenyllactate. They retain, however, a cytoplasmic NAD(+)-linked lactate dehydrogenase (nLDH). Since the mutants retained the ability to grow on lactate as a sole source of carbon, nLDH presumably can function in an opposite-to-normal physiological direction in the absence of iLDH. This would explain the failure to isolate iLDH-deficient mutants by selection for inability to grow on lactate.
Hendry
A T
AT
Department of Laboratory Medicine, Hamilton General Hospital, Ontario, Canada.
Bhatnagar
R K
RK
Shanmugam
K T
KT
Jensen
R A
RA
D004352:Drug Resistance, Microbial / Q000502:physiology; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase / Q000172:deficiency*; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D009154:Mutation; D009344:Neisseria gonorrhoeae / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D010648:Phenylacetates / Q000494:pharmacology; D010666:Phenylpropionates / Q000378:metabolism
D007527:Isoenzymes; D007773:Lactates; D010648:Phenylacetates; D010666:Phenylpropionates; C001418:4-hydroxyphenyllactic acid; D019344:Lactic Acid; D007770:L-Lactate Dehydrogenase; C025136:phenylacetic acid