Degradation Characteristics Of Dimethyl Isophthalate And Formaldehyde By Two Marine Fungi

Phthalate esters (PAEs) are used as plasticizers in plastic products and these compounds have been identified as toxic pollutants due to their endocrine-disrupting activity. With the rapid development of plastic industry, PAEs may pose serious threat in marine ecosystem. In our previous study, a marine fungus Fusarium sp. DMT-5-3capable of degrading PAEs was isolated from mangrove sediments by enrichment technique. Biochemical degradation pathways for different isomers of dimethyl phthalate esters (DMPEs) by the fungus were different, indicating that phthalate esterases involved are highly substrate specific. In this study, an intracellular esterase was isolated from the fungus Fusarium sp. DMT-5-3with dimethyl isophthalate (DMI) as the inducing substrate. The esterase was purified by ion-exchange chromatography and gel-filtration chromatography in sequence. The purified enzyme is a polymeric protein consisting of two identical subunits with a molecular mass of about76kDa. The enzyme showed a maximum esterase activity at50℃and was stable below40℃. The optimal pH was8.0and the enzyme was stable between pH6.0and12.0. Cr3+, Cu2+, and Hg2+were able to strongly inhibit the esterase activity, while Mg2+, Ca2+, and Sr2+can increase the enzymatic activity. Substrate specificity analysis showed that the enzyme was specific to the hydrolysis of DMI and dimethyl terephthalate (DMT), but had no effect on dimethyl phthalate (DMP) or monomethyl phthalate ester isomers. Enzymatic characteristic analyses showed that this DMI esterase was different with the DMT esterase previously isolated from Fusarium sp. DMT-5-3, suggesting that this marine fungus was capable of producing different esterase involved in hydrolysis of different DMPE isomers.Formaldehyde (HCHO) is widely applied in marine aquaculture as a disinfectant. Formaldehyde is highly toxic to marine organisms because of non-specific reactivity with proteins and nucleic acids. In the present study, a formaldehyde-degrading fungus DY-F2was isolated from deep sea seidiments of East Pacific Ocean. The fungus was identified as Penicillium chrysogenum DY-F2based on microscopic spore morphology and18S rRNA gene sequence analysis. The fungus showed high formaldehyde resistance and was able to grow in the presence of formaldehyde up to3000mg/1. The optimal temperature and pH for the growth of fungus in the presence of1000mg/1of formaldehyde was25℃and6.0, respectively. The fungus was able to degrade formaldehyde as the sole source of carbon and energy with the formation of formic acid as the intermediate. Degradation of formaldehyde by the fungus conformed to a first-order kinetic model. This study suggested that the deep sea sediment fungi are the potential microbial resources for bioremediation of formaldehyde pollution in marine environment.