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Disruption of the 2-methylcitric acid cycle and evaluation of poly-3-hydroxybutyrate-co-3-hydroxyvalerate biosynthesis suggest alternate catabolic pathways of propionate in Burkholderia sacchari

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Abstract:

The objective of the present work was to evaluate the relevance of the 2-methylcitric acid cycle (2MCC) to the catabolism of propionate in Burkholderia sacchari. Two B. sacchari mutants unable to grow on propionate were obtained: one disrupted in acnM, and the other in acnM and prpC deleted. An operative 2MCC significantly reduces the bacterial ability to incorporate 3-hydroxyvalerate (3HV) into a biodegradable copolyester accumulated from carbohydrates plus propionate. The efficiency of the mutants in converting propionate to 3HV units (Y3HV/prp) increased from 0.09 g·g-1 to 0.81-0.96 g·g-1, indicating that acnM and prpC are both essential for growth on propionate. None of the mutations resulted in achievement of the maximum theoretical Y3HV/prp (1.35 g·g-1). When increasing concentrations of propionate were supplied, decreasing values of Y3HV/prp were observed. The results obtained corroborate the hypothesis of the presence of other propionate catabolic pathways in B. sacchari. The 2MCC would be the more operative pathway, but a second pathway, which remains to be elucidated, would assume more importance under propionate concentrations of 1 g·L-1 or higher. The efficiency in converting propionate to 3HV units can be improved by decreasing the propionate concentrations, owing to the role of the 2MCC.

L’objectif de ce travail était d’évaluer l’implication du cycle du 2-méthyl citrate (C2MC) sur le catabolisme du propionate chez Burkholderia sacchari. Deux mutants de B. sacchari incapables de croître sur le propionate ont été obtenus : un mutant dont le gène acnM était interrompu et un mutant dont les gènes acnM et prpC étaient supprimés. Un C2MC fonctionnel réduisait significativement la capacité bactérienne à incorporer le 3-hydroxyvalérate (3HV) dans le co-polyester biodégradable accumulé à partir des hydrates de carbone et du propionate. L’efficacité à convertir le propionate en unités de 3HV (Y3HV/prp) démontrée par les mutants augmentait de 0,09 g·g-1 à 0,81-0,96 g·g-1, indiquant que les gènes acnM et prpC sont tous deux essentiels à la croissance sur propionate. Aucune des mutations ne conduisait à l’atteinte du Y3HV/prp maximal théorique (1,35 g·g-1). Lorsque des concentrations croissantes de propionate étaient ajoutées, des valeurs de Y3HV/prp décroissantes étaient observées. Les résultats obtenus corroborent l’hypothèse de la présence d’autres sentiers cataboliques du propionate chez B. sacchari. Le C2MC serait plus opérant, mais un deuxième sentier qui reste à élucider serait plus important à des concentrations de propionate de 1 g·L-1 ou plus. L’efficacité de conversion du propionate en unités de 3HV peut être améliorée en diminuant les concentrations de propionate, à cause du rôle joué par le C2MC.

Document Type: Research Article

Publication date: 2009-06-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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