Development of highly efficient electrocompetent cells for electroporation of Geobacillus thermoglucosidasius NCIMB 11955 / 生物工程学报

Geobacillus thermoglucosidasius is a kind of Gram-positive facultative anaerobic bacteria. The fast growth rate under high temperature and less susceptibility to microbial contamination enable G. thermoglucosidasius to be a desirable producer of biofuels and high-value-added chemicals for the next-generation industrial biotechnology. However, compared with the classical model strain Escherichia coli, the applications of G. thermoglucosidasius are hampered by its low transformation efficiency. This study aimed at obtaining competent cells with high transformation efficiency through inactivating restriction enzymes, adding cell membrane inhibitors and cell wall weakening agents. The results showed that the electro-transformation efficiency achieved 1.2×104 CFU/(μg DNA) by knocking out four genes encoding restriction enzymes. Adding a certain amount of tween 80, dl-threonine and glycine further increased the competent efficiency about 22.5, 44, and 334 times, respectively. The electro-transformation efficiency was enhanced to 4.6×106 CFU/(μg DNA) under the optimized conditions, laying a foundation for genetic manipulation and metabolic engineering of G. thermoglucosidasius.

The conserved aspartate in motif III of b family AdoMet-dependent DNA methyltransferase is important for methylation

S-adenosyl-L-methionine (AdoMet)-dependent methyltransferases (MTases) are involved in diverse cellularfunctions. These enzymes show little sequence conservation but have a conserved structural fold. The DNAMTases have characteristic motifs that are involved in AdoMet binding, DNA target recognition and catalysis.Motif III of these MTases have a highly conserved acidic residue, often an aspartate, whose functionalsignificance is not clear. Here, we report a mutational study of the residue in the b family MTase of the Type IIIrestriction-modification enzyme EcoP15I. Replacement of this residue by alanine affects its methylationactivity. We propose that this residue contributes to the affinity of the enzyme for AdoMet. Analysis of thestructures of DNA, RNA and protein MTases reveal that the acidic residue is conserved in all of them, andinteracts with N6 of the adenine moiety of AdoMet. Interestingly, in the SET-domain protein lysine MTases,which have a fold different from other AdoMet-dependent MTases, N6 of the adenine moiety is hydrogenbonded to the main chain carbonyl group of the histidine residue of the highly conserved motif III. Our studyreveals the evolutionary conservation of a carbonyl group in DNA, RNA and protein AdoMet-dependentMTases for specific interaction by hydrogen bond with AdoMet, despite the lack of overall sequenceconservation