Abstract
BackgroundGenome characterization of the model PCB-degrading bacterium Burkholderia xenovorans LB400 revealed the presence of eleven central pathways for aromatic compounds degradation, among them, the homogentisate and the homoprotocatechuate pathways. However, the functionality of these central pathways in strain LB400 has not been assessed and related peripheral pathways has not been described.Methodology/Principal FindingsThe aims of this study were to determine the functionality of the homogentisate and homoprotocatechuate central pathways in B. xenovorans LB400 and to establish their role in 3-hydroxyphenylacetate (3-HPA) and 4-hydroxyphenylacetate (4-HPA) catabolism. Strain LB400 was able to grow using 3-HPA and 4-HPA as sole carbon source. A genomic search in LB400 suggested the presence of mhaAB and hpaBC genes clusters encoding proteins of the 3-hydroxyphenylacetate and 4-hydroxyphenylacetate peripheral pathways. LB400 cells grown with 3-HPA and 4-HPA degraded homogentisate and homoprotocatechuate and showed homogentisate 1,2-dioxygenase and homoprotocatechuate 2,3-dioxygenase activities. Transcriptional analyses by RT-PCR showed the expression of two chromosomally-encoded homogentisate dioxygenases (BxeA2725 and BxeA3900) and the hpaD gene encoding the homoprotocatechuate 2,3-dioxygenase during 3-HPA and 4-HPA degradation. The proteome analyses by two-dimensional polyacrilamide gel electrophoresis of B. xenovorans LB400 grown in 3-HPA and 4-HPA showed the induction of fumarylacetoacetate hydrolase HmgB (BxeA3899).Conclusions/SignificanceThis study revealed that strain LB400 used both homogentisate and homoprotocatechuate ring-cleavage pathways for 3- hydroxyphenylacetate and 4-hydroxyphenylacetate catabolism and that these four catabolic routes are functional, confirming the metabolic versatility of B. xenovorans LB400.
Highlights
Aromatic compounds are widely distributed in ecosystems mainly released from plant materials and by anthropogenic activities
This study showed that both homogentisate and homoprotocatechuate central pathways are involved in 3-HPA and 4-HPA degradation in strain LB400
This study has shown that the homogentisate and the homoprotocatechuate central pathways are involved in 3-HPA and 4-HPA catabolism by B. xenovorans strain LB400. 3-HPA and 4HPA isomers are used by B. xenovorans LB400 as sole carbon and energy source for growth, indicating active peripheral and central catabolic pathways
Summary
Aromatic compounds are widely distributed in ecosystems mainly released from plant materials and by anthropogenic activities. A broad range of aromatic compounds is degraded by bacteria through peripheral pathways that funnel into few central pathways [1,2,3]. Activation of the aromatic ring is commonly mediated by monooxygenases or dioxygenases that produce dihydroxylated intermediates. Central pathways involve the fission by a dioxygenase of the dihydroxylated aromatic metabolic intermediates at ortho- or meta-position and lead to the formation of Krebs cycle intermediates [1,2,3,4]. The metabolic reconstruction of aromatic compounds pathways in in model environmental bacteria has been achieved by genome sequence analyses [3,12,13,14]. Genome characterization of the model PCB-degrading bacterium Burkholderia xenovorans LB400 revealed the presence of eleven central pathways for aromatic compounds degradation, among them, the homogentisate and the homoprotocatechuate pathways. The functionality of these central pathways in strain LB400 has not been assessed and related peripheral pathways has not been described
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