A study of the central carbon metabolism pathways of slow and fast growing brucellae

Abstract

[Introducción] The brucellae are the agents of brucellosis, a worldwide-distributed zoonosis, that behave as facultative intracellular parasites able to adjust their metabolism to extra and intracellular environments. Brucella metabolism is imperfectly known and most work has been conducted with B. abortus and B. melitensis that, like most brucellae, grow slowly. B. microti and the closely related B. suis biovar 5 are fast growing, suggesting species differences in metabolic abilities.

[Métodos] To analyze the glyoxylate and gluconeogenic pathways in fast and slow growing brucellae, we constructed non-polar mutants in key enzymes of B. abortus and B. suis 5. We tested the mutants in two minimal media (glutamate-lactate-glycerol and erythritol) and in a rich medium. Finally, we studied their multiplication in macrophages and/or mice.

[Resultados] Disruption of the hypothetical isocitrate lyase in either strain had no effect suggesting that the glyoxylate cycle is not essential. In vitro, the B. suis 5 but not the B. abortus double Fbp-GlpX mutant grew under gluconeogenic conditions, suggesting a third fructose-1,6-bisphosphatase or an unknown gluconeogenic pathway. Fbp and GlpX were not essential in vivo even for B. abortus. With regards to phosphoenolpyruvate synthesis, there were differences in PckA between these strains but only PpdK was critical in both species in vivo. Although it is accepted that erythritol (a Brucella preferred carbon source) is converted into dihydroxyacetone-phosphate, the B. abortus double Fbp-GlpX mutant grew normally on this substrate. Finally, the B. abortus but not the B. suis 5 ppdK mutant was impaired on erythritol, suggesting that whereas B. suis 5 depends on Pyk to grow on erythritol, this enzyme may not be active in B. abortus.

[Conclusiones] The results suggest that: (i), whereas the upper gluconeogenic steps and the glyoxylate cycle are not necessary in vivo, phosphoenolpyruvate synthesis is required; (ii), erythritol is metabolized directly through the pentose cycle rather than through the accepted pathway; and (iii), there is an evolutionary tendency towards reduction of metabolic activities from fast to slow growing brucellae, consistent with the hypothesis that fast growing brucellae are closer to the ancestor. Although B. abortus in commonly used, research focused on this species offers only a partial view of the metabolism of Brucella.