Hydroxylation of ionized aromatics including carboxylic acid or amine using recombinant Streptomyces lividans cells expressing modified biphenyl dioxygenase genes

Metabolic and Evolutionary Insights in the Transformation of Diphenylamine by a Pseudomonas putida Strain Unravelled by Genomic, Proteomic, and Transcription Analysis

Diphenylamine (DPA) is a common soil and water contaminant. A Pseudomonas putida strain, recently isolated from a wastewater disposal site, was efficient in degrading DPA. Thorough knowledge of the metabolic capacity, genetic stability and physiology of bacteria during biodegradation of pollutants is essential for their future industrial exploitation. We employed genomic, proteomic, transcription analyses and plasmid curing to (i) identify the genetic network of P. putida driving the microbial transformation of DPA and explore its evolution and origin and (ii) investigate the physiological response of bacterial cells during degradation of DPA. Genomic analysis identified (i) two operons encoding a biphenyl (bph) and an aniline (tdn) dioxygenase, both flanked by transposases and (ii) two operons and several scattered genes encoding the ortho-cleavage of catechol. Proteomics identified 11 putative catabolic proteins, all but BphA1 up-regulated in DPA- and aniline-growing cells, and showed that the bacterium mobilized cellular mechanisms to cope with oxidative stress, probably induced by DPA and its derivatives. Transcription analysis verified the role of the selected genes/operons in the metabolic pathway: DPA was initially transformed to aniline and catechol by a biphenyl dioxygenase (DPA-dioxygenase); aniline was then transformed to catechol which was further metabolized via the ortho-cleavage pathway. Plasmid curing of P. putida resulted in loss of the DPA and aniline dioxygenase genes and the corresponding degradation capacities. Overall our findings provide novel insights into the evolution of the DPA degradation pathway and suggests that the degradation capacity of P. putida was acquired through recruitment of the bph and tdn operons via horizontal gene transfer.

Hydroxylation of anilides by engineered cytochrome P450BM3

Cytochrome P450_BM3mutants achieve selectivepara-hydroxylation of substitutedN-sulfonylanilines under mild conditions.

Pathway and evolutionary implications of diphenylamine biodegradation by Burkholderia sp. strain JS667

Diphenylamine (DPA) is a common contaminant at munitions-contaminated sites as well as at aniline manufacturing sites. Little is known about the biodegradation of the compound, and bacteria able to use DPA as the growth substrate have not been reported. Burkholderia sp. strain JS667 and Ralstonia sp. strain JS668 were isolated by selective enrichment from DPA-contaminated sediment. The isolates grew aerobically with DPA as the sole carbon, nitrogen, and energy source. During induction of DPA degradation, stoichiometric amounts of aniline accumulated and then disappeared, which suggested that aniline is on the DPA degradation pathway. Genes encoding the enzymes that catalyze the initial steps in DPA degradation were cloned from the genomic DNA of strain JS667. The Escherichia coli clone catalyzed stoichiometric transformation of DPA to aniline and catechol. Transposon mutagenesis, the sequence similarity of putative open reading frames to those of well-characterized dioxygenases, and (18)O(2) experiments support the conclusion that the initial reaction in DPA degradation is catalyzed by a multicomponent ring-hydroxylating dioxygenase. DPA is converted to aniline and catechol via dioxygenation at the 1,2 position of the aromatic ring and spontaneous rearomatization. Aniline and catechol are further biodegraded by the well-established aniline degradation pathway. Genes that encode the complete aniline degradation pathway were found 12 kb downstream of the genes that encode the initial dioxygenase. Expression of the relevant dioxygenases was confirmed by reverse transcription-PCR analysis. Both the sequence similarity and the gene organization suggest that the DPA degradation pathway evolved recently by the recruitment of two gene clusters that encode the DPA dioxygenase and aniline degradation pathway.

Synthesis of highly hydroxylated aromatics by evolved biphenyl dioxygenase and subsequent dihydrodiol dehydrogenase

The evolved bphA1 (2049) gene, in which nine amino acids from the Pseudomonas pseudoalcaligenes KF707 BphA1 were changed to those from the Burkholderia xenovorans LB400 BphA1 (M247I, H255Q, V258I, G268A, D303E, -313G, S324T, V325I, and T376N), was expressed in Escherichia coli along with the bphA2A3A4 and bphB genes derived from strain KF707. This recombinant E. coli cells converted biphenyl and several heterocyclic aromatic compounds into the highly hydroxylated products such as biphenyl-2,3,2',3'-tetraol (from biphenyl), 2-(2,3-dihydroxyphenyl)benzoxazole-4,5-diol (from 2-phenylbenzoxazole), and 2-(2,5-dihydroxyphenyl)benzoxazole-4,5-diol [from 2-(2-hydroxyphenyl)benzoxazole]. The antioxidative activity of these generated compounds was markedly higher than that of the original substrate used.