Enhancement of photo-driven biomethanation under visible light by nano-engineering of Rhodopseudomonas palustris.

Biomethanation is of great interest as it can transform CO2 to methane under ambient conditions. In particular, genetically engineered bacterium of Rhodopseudomonas palustris showed great promise for one-step biomethanation powered by solar energy, which is attractive for CO2 fixation as well as solar energy storage. However, biomethanation with R. palustris under visible light is inefficient due to its poor visible light response. In this study, CdS quantum dots with excellent visible light response were prepared and R. palustris/CdS hybrid cells were constructed. Interestingly, this bio-nano-hybrid cells showed high cell viability without significant cell damage, and the biomethanation performance of was enhanced about ~ 79% compared to that of the bare R. palustris cells. Moreover, the effects of different parameters on the methane production of this bio-nano-hybrid cells were determined, and the methane production rate was further improved by parameter optimization. This work demonstrated an efficient approach to reinforce the biomethanation of bacteria under unfavorable light wavelength, which would be helpful to extend the light spectra for photo-driven biomethanation.

Characterization of EstZY: A new acetylesterase with 7-aminocephalosporanic acid deacetylase activity from Alicyclobacillus tengchongensis.

Deacetyl-7-aminocephalosporanic acid (D-7-ACA) is required for producing of many semisynthetic ß-lactam antibiotics; therefore, enzymes capable of converting 7-aminocephalosporanic acid (7-ACA) to D-7-ACA present a valuable resource to the pharmaceutical industry. In the present study, a putative acetylesterase, EstZY, was identified and characterized from a thermophilic bacterium Alicyclobacillus tengchongensis. Sequence alignment showed that EstZY was an acetylesterase which belonged to carbohydrate esterase family 7 (CE7), with substrate preference for short-chain acyl esters p-NPC2 to p-NPC8. Maximum enzyme activity was recorded at pH 9.0 and 50 °C, where Km and Vmax were calculated as 1.9 ± 0.23 mM and 258 ± 18.5 µM min-1, respectively. The residues Ser185, Asp274, and His303 were identified as the putative catalytic triad by homology modelling, site-directed mutagenesis and molecular docking. Moreover, EstZY can remove the acetyl group at C3' position of 7-ACA to form D-7-ACA; this is the first report of a 7-ACA deacetylase from CE7 family in A. tengchongensis and may represent a new enzyme with industrial values.

Identification and characterization of an acetyl esterase from Paenibacillus sp. XW-6-66 and its novel function in 7-aminocephalosporanic acid deacetylation.

OBJECTIVES: To obtain a new acetyl esterase from Paenibacillus sp. XW-6-66 and apply the enzyme to 7-aminocephalosporanic acid (7-ACA) deacetylation. RESULTS: The acetyl esterase AesZY was identified from Paenibacillus sp. XW-6-66, and its enzymatic properties were investigated. With the putative catalytic triad Ser114-Asp203-His235, AesZY belongs to the Acetyl esterase (Aes) family which is included in the α/ß hydrolase superfamily and contains the consensus Gly-X-Ser-X-Gly motif. The maximum activity of AesZY was detected at pH 8.0 and 40 °C. AesZY was stable at different pH values ranging from 5.0 to 12.0, and was tolerant to several metal ions. Furthermore, the deacetylation activity of AesZY toward 7-ACA was approximately 7.5 U/mg, and the Kcat/Km value was 2.04 s-1 mM-1. CONCLUSIONS: Our results demonstrate the characterization of a new acetyl esterase belonging to the Aes family with potential biotechnological applications.

A thermostable and alkaline GDSL-motif esterase from Bacillus sp. K91: crystallization and X-ray crystallographic analysis.

The esterase Est8 from the thermophilic bacterium Bacillus sp. K91 belongs to the GDSL family and is active on a variety of acetylated compounds, including 7-aminocephalosporanic acid. In contrast to other esterases of the GDSL family, the catalytic residues Asp182 and His185 were more pivotal for the catalytic activity of Est8 than the Ser11 residue. To better understand the biochemical and enzymatic properties of Est8, recombinant Est8 protein was purified and crystallized. Crystals of Est8 were obtained by the hanging-drop vapour-diffusion method using 2.0 M ammonium sulfate, 5%(v/v) 2-propanol as the crystallization solution. X-ray diffraction data were collected to a resolution of 2.30 Šwith an Rmerge of 16.4% from a crystal belonging to space group P41212 or P43212, with unit-cell parameters a = b = 68.50, c = 79.57 Å.