Two Different O-Demethylation Enzymic Systems in Lignin Metabolism of Soil Bacterium and Clonig of Lignin Biphenyl Specific O-Demethylase Gene

少动鞘氨醇单胞菌SYK-6是一种从生物圈中分离出来的细菌，可以在各种木质素二聚化合物（包括丁香酸盐、香草酸盐和5，5 '-脱氢二香草酸盐（DDVA，木质素联苯化合物））作为唯一来源上生长。在我们以前的研究中，已经确定了DDVA和其他二聚体化合物的代谢途径以及这些途径的许多必需基因，然而，对于双甘酯、香草酸和DDVA的O-去甲基化反应，在本研究中，我们证明了胡萝卜酸和香草酸的O-去甲基化是四氢叶酸（THF）依赖的甲基转移酶反应体系，而少动链球菌SYK-6的THF依赖性酶对DDVA（木质素联苯化合物）没有活性。我们还表明，少动链球菌SYK-6中的DDVA O-去甲基化是一个含氧脱甲基酶系统，如细胞色素P-450，并表明两个不同的脱甲基系统存在于少动鞘氨醇单胞菌SYK-6。在本研究中，我们成功地克隆了少动链球菌SYK-6中负责DDVA O-去甲基化的基因（ligX）。

Sphingomonas paucimobilis SYK-6, a bacterium that can grow on various lignin dimeric compounds that include syringate, vanillate and 5,5'-dehydrodivanillate (DDVA, lignin biphenyl compound) as a sole source, was isolated from biosphere. The metabolic pathways of DDVA and other dimeric compounds and the many essential genes for the pathways have been identified in our previous studies, however the O-demethylation reactions for syringate, vanillate and DDVA(lignin biphenyl compound) have not been investigated.In this study, we show that the O-demethylation of syringate and vanillate is the tetrahydrofolate(THF)-dependent methyltransferase reaction system, whereas the THF-dependent enzyme of S paucimobilis SYK-6 has no activity on DDVA(lignin biphenyl compound). We also show that DDVA O-demethylation in S paucimobilis SYK-6 is an oxygenative demethylase system such as cytochrome P-450 and show that two different demethylation systems exist in Sphingomonas paucimobilis SYK-6. In this study, we succeed molecular cloning the gene (ligX) responsible for the DDVA O-demethylation in S paucimobilis SYK-6.