Abstract
BackgroundAs an environmental pollutant, 4-hydroxyphenylacetate (4-HPA) was a product of softwood lignin decomposition and was found in industrial effluents from olive oil production. Sulfobacillus acidophilus TPY was a moderately thermoacidophilic bacterium capable of degrading aromatic compounds including 4-HPA. The enzymes involved in the degradation of 4-HPA and the role of this strain in the bioremediation of marine pollutants need to be illustrated.Results3,4-dihydroxyphenylacetate dioxygenase (DHPAO) encoded by mhpB2 and two components of 4-hydroxydroxyphenylacetate (4-HPA) 3-hydroxylase encoded by hpaB and hpaC from S. acidophilus TPY, a moderately thermoacidophilic bacterium, involved in the degradation of 4-HPA possessed quite low amino acid sequence identity (22–53%) with other ever reported corresponding enzymes, which suggest their novelty. These two enzymes were expressed in E. coli and purified to homogeneity. DHPAO activity in E. coli was revealed by spraying with catechol or 3,4-dihydroxyphenylacetate (3,4-DHPA) on the colonies to make them turn brilliant yellow color. DHPAO possessed total activity of 7.81 U and 185.95 U/mg specific activity at the first minute when 3,4-DHPA was served as substrate. DHPAO was a thermophilic enzyme with optimum temperature of 50 °C and optimum substrate of 3,4-DHPA. The small component (HpaC) was a flavoprotein, and both HpaB and HpaC of 4-HPA 3-hydroxylase were NADH-dependent and essential in the conversion of 4-HPA to 3,4-DHPA. 4-HPA 3-hydroxylase possessed 3.59 U total activity and 27.37 U/mg specific activity at the first minute when enzymatic coupled assay with DHPAO was applied in the enzymatic determination.ConclusionsThe ability of this extreme environmental marine strain to degrade catechol and substituted catechols suggest its applications in the bioremediation of catechol and substituted catechols polluted marine environments.
Highlights
As an environmental pollutant, 4-hydroxyphenylacetate (4-HPA) was a product of softwood lignin decomposition and was found in industrial effluents from olive oil production
The a.a. identity of DHPAO from S. acidophilus TPY was significantly low with other corresponding enzymes, the putative metal ligand binding residues His-146, His-209 and Glu-262, the catalytic residues His-195, His-243 and Tyr-252 and three other residues Gly-32, Leu-165, Pro-256 were strictly conserved with other extradiol dioxygenases (Additional file 1: Figure S1)
These results indicated that DHPAO and 4-HPA 3-hydroxylase from S. acidophilus
Summary
4-hydroxyphenylacetate (4-HPA) was a product of softwood lignin decomposition and was found in industrial effluents from olive oil production. Catechol and substituted catechols were the key intermediate of the catabolic pathway of aromatic compounds [1]. Catabolism of phenolic compounds was often initiated by hydroxylases that incorporate hydroxyl groups into phenolic substrates, resulting in production of a few intermediates such as catechol and substituted catechols [2]. These intermediates served as substrates for cleavage of the aromatic ring and could be further metabolized by two distinct sets of enzymes, which were responsible for the ortho- and meta- cleavage pathways [3]. The metal cofactors of DHPAOs from different species show significant diversity and include Fe(II), Mn(II) and Mg(II) [9]
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