1. Isolation of the (+)-Pinoresinol-Mineralizing Pseudomonas sp. Strain SG-MS2 and Elucidation of Its Catabolic Pathway.
- Author
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Shettigar, Madhura, Balotra, Sahil, Cahill, David, Warden, Andrew C., Lacey, Michael J., Kohler, Hans-Peter E., Rentsch, Daniel, Oakeshott, John G., and Pandey, Gunjan
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PLANT defenses , *LIGNIN biodegradation , *SHIKIMIC acid , *PSEUDOMONAS , *BACTERIAL metabolism - Abstract
Pinoresinol is a dimer of two β-β=-linked coniferyl alcohol molecules. It is both a plant defense molecule synthesized through the shikimic acid pathway and a representative of several β-β-linked dimers produced during the microbial degradation of lignin in dead plant material. Until now, little has been known about the bacterial catabolism of such dimers. Here we report the isolation of the efficient (β)- pinoresinol-mineralizing Pseudomonas sp. strain SG-MS2 and its catabolic pathway. Degradation of pinoresinol in this strain is inducible and proceeds via a novel oxidative route, which is in contrast to the previously reported reductive transformation by other bacteria. Based on enzyme assays and bacterial growth, cell suspension, and resting cell studies, we provide conclusive evidence that pinoresinol degradation in strain SG-MS2 is initiated by benzylic hydroxylation, generating a hemiketal via a quinone methide intermediate, which is then hydrated at the benzylic carbon by water. The hemiketal, which stays in equilibrium with the corresponding keto alcohol, undergoes an aryl-alkyl cleavage to generate a lactone and 2-methoxyhydroquinone. While the fate of 2-methoxyhydroquinone is not investigated further, it is assumed to be assimilated by ring cleavage. The lactone is further metabolized via two routes, namely, lactone ring cleavage and benzylic hydroxylation via a quinone methide intermediate, as described above. The resulting hemiketal again exists in equilibrium with a keto alcohol. Our evidence suggests that both routes of lactone metabolism lead to vanillin and vanillic acid, which we show can then be mineralized by strain SG-MS2. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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