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

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 p N–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.