枯草芽孢杆菌CAS15嗜铁素基因dhbC的克隆、表达及功能鉴定

Cloning,expression and functional analysis of the dhbC gene from the siderophore producing bacterium Bacillus subtilis CAS15

通过PCR技术扩增得到dhbC基因,对其进行序列分析发现,dhbC基因片段长为1197bp,预期编码398个氨基酸,蛋白分子量大小为43.8kD。将目的片段连接到表达载体pET-30a(+),转化大肠杆菌Escherichia coli BL21(DE3)获得重组菌株BL21(DE3)/pET-30a-dhbC,以IPTG在30oC诱导4h实现高效表达,获得一个分子量为48.8kD的融合蛋白。重组蛋白可溶性分析结果表明:融合蛋白主要为可溶性蛋白。Western blotting分析结果表明:重组蛋白可与兔抗His-tag多克隆抗体发生特异性反应,在48.8kD处有特异条带,与预期结果一致,证明重组质粒中含有dhbC基因。通过同源重组的策略将dhbC基因敲除后重新导入,验证了dhbC基因与嗜铁素的生物合成密切相关。

We amplified dhbC gene from the siderophore producing bacterium CAS15 by PCR. After ligated the PCR product to pMD18-T vector and then sequenced, we obtained a 1197 bp fragment. The blast result showed that the nucleotide acids of dhbC gene （Accession No. FJ 194456） of CAS 15 shared 99.7% identity with that of dhbC gene of Bacillus subtilis （GenBank Accession No Z99120）, and was predicted to encode a 43.8 kD polypeptide with 398 amino acid residues. We cloned the dhbC gene into expression vector pET-30a（＋） and then transformed into Escherichia coli BL21（DE3） via calcium chloride transformation method, and obtained the recombinant E. coli BL21（DE3）/pET-30a-dhbC. Induced by 1 mmol/L IPTG, the fusion protein 6His-DhbC, a 48.8 kD polypeptide was successfully expressed mainly in soluble form in E. coli BL21（DE3）, and the amount reached highest at 30℃ for 4 h. According to the N-terminal fusion 6 His-tag, we purified the recombinant polypeptide by Ni^2＋ metal affinity chromatography and finally identified it by Western blotting. The result indicated that the recombinant DhbC had the antigenicity to rabbit anti-his-tag polyclonal antibody, which provides the basis for the study of practical utilization in production and the biocontrol mechanism of B. subtilis. Finally, we deleted dhbC gene by gene knockout and then retransformed it into the dhbC gene-delected mutant, which confirmed that dhbC gene play an important role in siderophore biosynthesis.