Degradation of Dimethyl Isophthalate by Viarovorax paradoxus Strain T4 Isolated from Deep-Ocean Sediment of the South China Sea

ABSTRACT

Viarovorax paradoxusT4 strain was isolated from deep-ocean sediment and demonstrated to be able to degrade dimethyl isophthalate (DMI). When DMI was utilized as the sole source of carbon and energy, it was transformed by hydrolysis initially, forming monomethyl isophthalate (MMI) and isophthalate acid (IA) as degradation intermediates. DMI and MMI were completely transformed to MMI and IA in about 100 h, respectively. Degradation of IA was completed in about 55 h. Analysis of total organic carbon in the culture medium confirmed that more than 80% of the substrate carbon was mineralized. Bacterial esterase induced by a range of substrates could be assessed using p-nitrophenyl acetate as the common substrate using crude enzyme preparation. The decreasing trend of K _m values derived from the Michaelis–Menten equation was dimethyl phthalate (DMP) > monomethyl phthalate (MMP) > dimethyl terephthalate (DMT) > Liver esterase > DMI > MMI > monomethyl terephthalate (MMT), indicating that higher K _m values were obtained by di-esters than mono-ester and the esters induced by terephthalate esters showed the highest activity. This investigation suggests that biochemical pathways for phthalate esters share many common characteristics and the esterases induced by different substrates are highly specific.

Key Words:

• plasticiser
• dimethyl isophthalate
• monoisophthalate
• isophthalate
• biochemical pathway
• esterase.

ACKNOWLEDGMENTS

This research was financially supported by RGC Central Allocation CA00/01.SC01 and 863 Project (No. 2002AA601160) supplement fund by The University of Hong Kong. We thank Li Pan for the determination of the 16S rDNA sequence of the bacterium.