Characterization of Thermotoga maritima Esterase Capable of Hydrolyzing Bis(2-hydroxyethyl) Terephthalate

Abstract

The gene-encoding carboxylesterase (TM1022) from the hyperthermophilic bacterium Thermotoga maritima (T. maritima) was cloned and expressed in Escherichia coli Top10 and BL21 (DE3). Recombinant TM1022 showed the best activity at pH 8.0 and 85 °C and retained 57% activity after 8 h cultivation at 90 °C. TM1022 exhibited good stability at pH 6.0−9.0, maintaining 53% activity after incubation at pH 10.0 and 37 °C for 6 h. The esterase TM1022 exhibited the optimum thermo-alkali stability and k cat /K m (598.57 ± 19.97 s −1 mM −1 ) for pN−C4. TM1022 hydrolyzed poly(ethylene terephthalate) (PET) degradation intermediates, such as bis(2-hydroxyethyl) terephthalate (BHET) and mono(2-hydroxyethyl) terephthalate (MHET). The K m , k cat , and k cat /K m values for BHET were 0.82 ± 0.01 mM, 2.20 ± 0.02 s −1 , and 2.67 ± 0.02 mM −1 s −1 , respectively; those for MHET were 2.43 ± 0.07 mM, 0.04 ± 0.001 s −1 , and 0.02 ± 0.001 mM −1 s −1 , respectively. When purified TM1022 was added to the cutinase BhrPETase, hydrolysis of PET from drinking water bottle tops produced pure terephthalic acids (TPA) with 166% higher yield than those obtained after 72 h of incubation with BhrPETase alone as control. The above findings demonstrate that the esterase TM1022 from T. maritima has substantial potential for depolymerizing PET into monomers for reuse.