Absence of a functional glyoxalase system in Candidatus Liberibacter asiaticus confirms that the bacterium scavenges host cells for its energy requirements
M. JAIN (1), L. Fleites (2), S. Zhang (2), D. Gabriel (2) (1) Department of Plant Pathology, University of Florida, U.S.A.; (2) Department of Plant Pathology, University of Florida, U.S.A.

Methylglyoxal (MG) is a cytotoxic metabolite produced non-enzymatically from the glycolysis intermediates glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. MG is a potent electrophile that readily glycates arginine residues resulting in carbonyl stress. Glyoxalase I and II (GloI and GloII) sequentially convert MG into D-lactic acid using glutathione (GSH) as a cofactor. Conserved across all domains of life, the glyoxalase system is essential for the mitigation of MG-induced carbonyl stress, preventing subsequent cell death, and recycling GSH for maintenance of cellular redox poise. In silico analysis surprisingly revealed that the uncultured, intracellular and lethal citrus pathogen Candidatus Liberibacter asiaticus (Las) lacks GloI, the first enzyme of the MG detoxification system. Both GloI and GloII are, however, found in all cultured bacteria, including L. crescens (Lcr). Quantitative RT-PCR revealed significant downregulation of two key glycolytic pathway enzymes of Las (in both plant and insect hosts) as compared with Lcr in culture. Since Las has a functional ATP translocase, an unusual feature of intracellular prokaryotes and plastids, loss of the MG detoxification pathway could be tolerated if Las circumvents MG generation and directly imports ATP from host cells. Marker interruption of gloI in Lcr appears to be lethal. The stringent energy dependence of Las on its host cell may be an important determinant making Las recalcitrant towards in vitro culturing.

Abstract Number: P9-264
Session Type: Poster