Conversion from Arenes Having a Benzene Ring to Those Having a Picolinic Acid by Simple Growing Cell Reactions Using Escherichia coli that Expressed the Six Bacterial Genes Involved in Biphenyl Catabolism

Plant exudates promote PCB degradation by a rhodococcal rhizobacteria

Rhodococcus erythropolis U23A is a polychlorinated biphenyl (PCB)-degrading bacterium isolated from the rhizosphere of plants grown on a PCB-contaminated soil. Strain U23A bphA exhibited 99% identity with bphA1 of Rhodococcus globerulus P6. We grew Arabidopsis thaliana in a hydroponic axenic system, collected, and concentrated the plant secondary metabolite-containing root exudates. Strain U23A exhibited a chemotactic response toward these root exudates. In a root colonizing assay, the number of cells of strain U23A associated to the plant roots (5.7 × 10⁵ CFU g⁻¹) was greater than the number remaining in the surrounding sand (4.5 × 10⁴ CFU g⁻¹). Furthermore, the exudates could support the growth of strain U23A. In a resting cell suspension assay, cells grown in a minimal medium containing Arabidopsis root exudates as sole growth substrate were able to metabolize 2,3,4'- and 2,3',4-trichlorobiphenyl. However, no significant degradation of any of congeners was observed for control cells grown on Luria-Bertani medium. Although strain U23A was unable to grow on any of the flavonoids identified in root exudates, biphenyl-induced cells metabolized flavanone, one of the major root exudate components. In addition, when used as co-substrate with sodium acetate, flavanone was as efficient as biphenyl to induce the biphenyl catabolic pathway of strain U23A. Together, these data provide supporting evidence that some rhodococci can live in soil in close association with plant roots and that root exudates can support their growth and trigger their PCB-degrading ability. This suggests that, like the flagellated Gram-negative bacteria, non-flagellated rhodococci may also play a key role in the degradation of persistent pollutants.

Dioxygenase-catalysed cis-dihydroxylation of meta-substituted phenols to yield cyclohexenone cis-diol and derived enantiopure cis-triol metabolites

cis-Dihydroxylation of meta-substituted phenol (m-phenol) substrates, to yield the corresponding cyclohexenone cis-diol metabolites, was catalysed by arene dioxygenases present in mutant and recombinant bacterial strains. The presence of cyclohexenone cis-diol metabolites and several of their cyclohexene and cyclohexane cis-triol derivatives was detected by LC-TOFMS analysis and confirmed by NMR spectroscopy. Structural and stereochemical analyses of chiral ketodiol bioproducts, was carried out using NMR and CD spectroscopy and stereochemical correlation methods. The formation of enantiopure cyclohexenone cis-diol metabolites is discussed in the context of postulated binding interactions of the m-phenol substrates at the active site of toluene dioxygenase (TDO).

Protein engineering on biphenyl dioxygenase for conferring activity to convert 7-hydroxyflavone and 5,7-dihydroxyflavone (chrysin)

A central part (amino-acid position 268-397 of 458 amino-acid residues) of the biphenyl dioxygenase large (alpha) subunit, BphA1, from Pseudomonas pseudoalcaligenes strain KF707 was exchanged with the corresponding part of BphA1 from another biphenyl-degrading bacterium, Pseudomonas putida strain KF715, to construct hybrid BphA1, BphA1 (715-707). When expressed in Escherichia coli together with the bphA2A3A4BC genes from strain KF707, this enzyme was shown to possess activity for degrading both 1-phenylnaphthalene and 2-phenylnaphthalene. Between central parts of BphA1 from strains KF707 and KF715, the difference of amino-acid residues resided only in position 324-325. An attempt was made to improve the substrate preference of BphA1 by applying random amino-acid substitutions at these positions to BphA1 (715-707). After screening the mutant library to bioconvert several flavonoids, BphA1 (1-22; T324A and I325L) and BphA1 (2-2; T324L and I325I) were selected. When expressed in E. coli together with bphA2A3A4B from strain KF707, both BphA1 (1-22) and BphA1 (2-2) bioconverted the refractory flavonoids, 7-hydroxyflavone and 5,7-dihydroxyflavone (chrysin), which were hardly converted by any unmodified and artificially-modified shuffled biphenyl dioxygeneses, into their vicinal diol forms, i.e., 2-(2,3-dihydroxyphenyl)-7-hydroxy-chromen-4-one and 2-(2,3-dihydroxyphenyl)-5,7-dihydroxy-chromen-4-one, respectively. In addition, trans-chalcone was converted into 3-(2,3-dihydroxyphenyl)-1-phenylpropan-1-one and further into 1,3-bis-(2,3-dihydroxyphenyl)-propan-1-one. The antioxidative activity of these generated compounds was markedly higher than that of the original substrates used.

A novel diol-derivative of chalcone produced by bioconversion, 3-(2,3-dihydroxyphenyl)-1-phenylpropan-1-one, activates PKA/MEK/ERK signaling and antagonizes Abeta-inhibition of the cascade in cultured rat CNS neurons

Chalcone compounds have been widely studied for their anti-inflammatory, anti-pyretic, anti-invasive and anti-proliferative activities in various cell lines. However, their effects on the central nervous system (CNS) are still largely unexplored. We have recently developed a bioconversion system using a recombinant Escherichia coli that enables us to produce chemical compounds that are naturally rare and usually difficult to chemically synthesize. One such compound is 3-(2,3-dihydroxyphenyl)-1-phenylpropan-1-one, a novel chalcone-diol. Here we show, for the first time, that the chalcone-diol enhanced the phosphorylation of extracellular signal-regulated kinase (ERK) in a time- and concentration-dependent manner in cultured cortical neurons. Also, this chalcone-diol increased intracellular cyclic AMP (cAMP) concentration, thereby enhancing phosphorylation of ERK and cAMP-response element-binding protein (CREB), and CRE-mediated transcription via the cAMP-dependent protein kinase (PKA)/mitogen-activated protein kinase/ERK kinase (MEK) pathway in cultured rat hippocampal neurons. Recent studies have demonstrated that PKA/CREB-dependent signaling, which is required for long-term potentiation, is inhibited by sublethal concentrations of amyloid beta-peptide (Abeta) in cultured hippocampal neurons. After treatment with the chalcone-diol at 50 muM prior to treatment with a sublethal concentration of Abeta(1-42), the Abeta(1-42)-induced inhibition of phosphorylation of PKA substrates and CREB was prevented in cultured hippocampal neurons, indicating the potential for protection against the Abeta-induced impairment of PKA/CREB signaling observed in Alzheimer's disease. Therefore, these results suggest that our present study provides a new approach for discovering novel lead compounds for the treatment of neurodegenerative CNS diseases associated with impaired PKA/CREB signaling, including Alzheimer's disease.