Wenqian Li,Hao Shi,Huaihai Ding,Liangliang Wang,Yu Zhang,Xun Li,Fei Wang
This paper first describes characterization of two thermostable esterases (ThLip1 and ThLip2) from the thermophilic bacterium Thermoanaerobacterium thermosaccharolyticum DSM 571. The recombinant esterase ThLip1 was active at 80 °C, pH 6.5 and maintained approx. 85% of original activity after 2 h incubation at 75 °C. Kinetic parameters , K m , V max and k cat / K m for 4-Nitrophenyl caprylate ( p NPC) were 3.52 ± 0.47 mM, 191.18 ± 1.82 μmol min −1 mg −1 and 20.80 ± 0.07 mM −1 s −1 , respectively. The purified recombinant esterase ThLip2 was optimally active at pH 6.5 and 75 °C and it was stable against a pH range of 6.0–8.0 possessing 2 h half-life at 80 °C. Kinetic experiments at 75 °C with p NPC as a substrate gave a K m of 3.37 mM, V max of 578.14 μmol min −1 mg −1 and k cat of 231.2 s −1 . The hydrolysis of linalyl acetate were carried out using ThLip1 and ThLip2 as catalyst, affording linalool yields over 140 mg/l in 10 h.
Microbial extracellular respiration is an important energy metabolism on earth, which is significant for the elemental biogeochemical cycle. Herein, extracellular Fe(III) and electrode respiration were confirmed in Thermoanaerobacterium thermosaccharolyticum MJ2 . The intra/extracellular electron transfer (IET/EET) mechanism of MJ2 was investigated by comparative genomic analysis for the first time. Morphological characterization and electrochemical properties of anode illustrated that MJ2 generated bio-electricity by forming a biofilm. The respiration chain inhibition and enzyme activity tests showed that hydrogenase with cytochrome c (Cyt- c ) was involved in IET of MJ2 . Noteworthily, the exogenous Cyt- c increased hydrogenase activity to promote bio-electricity generation by 92.84 %. The Cyt- c gene synteny between MJ2 and another well-known exoelectrogen ( Thermincola potens JR ) indicated that Cyt- c bound to the outer membrane mediated the formation of biofilm involved in EET of MJ2 . This study broadened the understanding of microbial extracellular respiration diversity and provided new insights to explore the electron transfer pathways of exoelectrogens.
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