1,2,4-Trihydroxybenzene

2-Chloro-4-nitrophenol (2C4NP) is the most common chlorinated nitrophenol pollutant, and its environmental fate is of great concern. Cupriavidus sp. CNP-8, a Gram-negative bacterium, has been reported to degrade 2C4NP via the 1,2,4-benzenetriol (BT) pathway, significantly different from the (chloro)hydroquinone pathways reported in all other Gram-negative 2C4NP-utilizers. Herein, the BT pathway of the catabolism of 2C4NP in this strain was characterized at the molecular, biochemical, and genetic levels. The hnp gene cluster was suspected to be involved in the catabolism of 2C4NP because the hnp genes are significantly upregulated in the 2C4NP-induced strain CNP-8 compared to the uninduced strain. HnpAB, a two-component FAD-dependent monooxygenase, catalyzes the conversion of 2C4NP to BT via chloro-1,4-benzoquinone, with a Km of 2.7 ± 1.1 μΜ and a kcat/Km of 0.17 ± 0.03 μΜ-1 min-1. hnpA is necessary for strain CNP-8 to utilize 2C4NP in vivo. HnpC, a BT 1,2-dioxygenase, was proved to catalyze BT ring-cleavage with formation of maleylacetate by HPLC-MS analysis. Phylogenetic analysis indicated that HnpA likely has different evolutionary origin compared to other functionally identified 2C4NP monooxygenases. To our knowledge, this is the first report revealing the catabolic mechanism of 2C4NP via the BT pathway in a Gram-negative bacterium, increasing our knowledge of the catabolic diversity for microbial 2C4NP degradation at the molecular and biochemical level.

Lignin is the most abundant aromatic compound in nature, and it plays an important role in the carbon cycle. White-rot fungi are microbes that are capable of efficiently degrading lignin. Enzymes from these fungi possess exceptional oxidative potential and have gained increasing importance for improving bioprocesses, such as the degradation of organic pollutants. The aim of this study was to identify the enzymes involved in the ring cleavage of the lignin-derived aromatic 1,2,4-trihydroxybenzene (THB) in Phanerochaete chrysosporium, a lignin-degrading basidiomycete. Two intradiol dioxygenases (IDDs), PcIDD1 and PcIDD2, were identified and produced as recombinant proteins in Escherichia coli. In the presence of O2, PcIDD1 and PcIDD2 acted on eight and two THB derivatives, respectively, as substrates. PcIDD1 and PcIDD2 catalyze the ring cleavage of lignin-derived fragments, such as 6-methoxy-1,2,4-trihydroxybenzene (6-MeOTHB) and 3-methoxy-1,2-catechol. The current study also revealed that syringic acid (SA) was converted to 5-hydroxyvanillic acid, 2,6-dimethoxyhydroquinone, and 6-MeOTHB by fungal cells, suggesting that PcIDD1 and PcIDD2 may be involved in aromatic ring fission of 6-MeOTHB for SA degradation. This is the first study to show 6-MeOTHB dioxygenase activity of an IDD superfamily member. These findings highlight the unique and broad substrate spectra of PcIDDs, rendering it an attractive candidate for biotechnological application. KEY POINTS: · Novel intradiol dioxygenases (IDD) in lignin degradation were characterized. · PcIDDs acted on lignin-derived fragments and catechol derivatives. · Dioxygenase activity on 6-MeOTHB was identified in IDD superfamily enzymes.

We report an improved method for synthesizing gold nanorods (GNRs) by using 1,2,4-trihydroxybenzene as a reducing agent. The method allows a rich array of monodispersed GNRs with longitudinal surface plasmon resonance (LSPR) tunable from 698 to 913 nm to be generated. A large range of diameter distribution of GNRs from 9.3 to 32.2 nm with exceptional monodispersity can be well prepared by this method. These findings indicate that this method has greater performance in controlling the morphology of GNRs than that of traditional approaches with ascorbic acid as a reductant.