Lactate dehydrogenases from Neisseria gonorrhoeae: molecular analysis and role in host cell/bacterial interactions

Ibranovic, Ines (2015). Lactate dehydrogenases from Neisseria gonorrhoeae: molecular analysis and role in host cell/bacterial interactions PhD Thesis, School of Chemistry and Molecular Biosciences, The University of Queensland. doi:10.14264/uql.2015.968

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Author Ibranovic, Ines
Thesis Title Lactate dehydrogenases from Neisseria gonorrhoeae: molecular analysis and role in host cell/bacterial interactions
Formatted title
Lactate dehydrogenases from Neisseria gonorrhoeae: molecular analysis and role in host cell/bacterial interactions
School, Centre or Institute School of Chemistry and Molecular Biosciences
Institution The University of Queensland
DOI 10.14264/uql.2015.968
Publication date 2015-10-23
Thesis type PhD Thesis
Supervisor Alastair McEwan
Cheryl Mines
Total pages 180
Total colour pages 19
Total black and white pages 161
Language eng
Subjects 0601 Biochemistry and Cell Biology
0605 Microbiology
Formatted abstract
Neisseria gonorrhoeae is an obligate human pathogen. It causes the sexually transmitted infection gonorrhoea that occurs on mucosal epithelia of the male urethra and female uterine cervix. Globally, there are more than sixty million cases of gonococcal infections reported every year that creates a high burden to the healthcare system. There are already cases reported of multi-drug resistant N. gonorrhoeae, where commonly used antibiotics for treatment of gonorrhoea cannot cure the infection.

Amongst different carbon sources N. gonorrhoeae can utilise only glucose, pyruvate and lactate efficiently. Studies have shown that phagocyte derived lactate, which accumulates as a consequence of glucose catabolism, stimulates oxygen consumption by N. gonorrhoeae. In addition, lactate is present at high concentrations in the female genito-urinary tract. This leads to the possibility that lactate metabolism is critical for the growth of N. gonorrhoeae. N. gonorrhoeae possesses at least three lactate dehydrogenase (Ldh) enzymes based on genome sequence analysis. However, the organisation and functional properties of these enzymes have not been fully defined. It was shown that two of the enzymes, D-lactate dehydrogenase (LdhD) and L-lactate dehydrogenase (LldD), are membrane-bound, independent of NAD+, and linked to respiratory electron transport. The third lactate dehydrogenase is a cytoplasmic NAD+ dependent D-lactate dehydrogenase (LdhA). It was observed that there was residual L-lactate dehydrogenase activity in the lldD mutant, suggesting the presence of an additional enzyme capable of oxidising lactate. A lutABC operon was identified in N. gonorrhoeae. Although homologous Lut enzymes in other bacteria have been shown to oxidise L-lactate analysis of lutABC mutants did not provide evidence for activity of LutABC towards L-lactate.

Mutants lacking the two respiratory lactate dehydrogenases were not able to survive in primary cervical epithelial (pex) cells under hypoxic conditions. Similarly, the lldD and ldhD mutants showed greatly reduced survival in neutrophils conpared to wild-type cells. Taken together these data show that host-derived lactate is critical for the growth and survival of N. gonorrhoeae in host cells.

Lactate is transported into the gonococcus by a lactate permease (LctP) transporter. Previous work in the murine model of infection, showed that a mutant lacking lctP failed to cause infection. The importance of the LctP transporter was confirmed by construction and analysis of an lctP mutant; this mutant was unable to grow with L-lactate as sole carbon source and showed reduced survival in neutrophils compared to wild-type gonococcus.
Keyword Neisseria gonorrhoea
Lactate metabolism
Host/cell interactions

Document type: Thesis
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Created: Wed, 14 Oct 2015, 17:13:39 EST by Ines Ibranovic on behalf of Scholarly Communication and Digitisation Service