地衣芽孢杆菌是重要的工业微生物，其食品安全特性（GRAS）、高效蛋白分泌能力与强抗逆性等优势使其广泛应用于酶制剂等产品的生物制造。然而，当前地衣芽孢杆菌缺乏多样性的表达调控元件，现有元件在强度及调控精密程度上不尽人意。木糖诱导启动子是该菌株已报道仅有的严谨调控表达元件之一，其受到的碳代谢物（如葡萄糖等）的严重阻遏限制了进一步应用。为了解决这一问题，本研究从分子机制出发改造启动子转录调控区，解除了碳代谢物对该启动子的严重阻遏。

利用来自B. licheniformis、B. megatherium和B. subtilis的生物元件构建了地衣芽孢杆菌木糖诱导表达系统,避免某些外源基因的表达对宿主细胞的生长带来威胁,使得生长与表达可控，并可能使两者的效率最大化。进一步的，在对碳代谢阻遏分子机制解析的基础上，对启动子非编码区推测转录因子结合位点（cre位点）的高保守序列和简并序列分别进行了分子改造，极大缓解了葡萄糖引起的阻遏效应，葡萄糖存在条件下表达强度较野生型提高了12倍。本研究首次揭示了地衣芽孢杆菌转录调控区cre位点不同碱基影响碳代谢阻遏效应的分子机制。

本文以“Development of an Inducible Secretory Expression System inBacillus licheniformisBased on an Engineered Xylose Operon”为题发表于“Journal of Agricultural and Food Chemistry”期刊，国工李由然为第一作者，石贵阳教授为通讯作者。这一研究受到了“十三五”国家重点研发计划（No. 2016YFD0401404）和国家自然科学基金（No. 31401674）的支持。

图注：Genetic organization of the B. licheniformis xylose regulon. The ORF encoding xylose isomerase (xylA) and the divergently oriented xylR gene are shown, and their respective gene products are indicated. The primary cre motif at +1253 and the putative cre site (cre*) at -10 are indicated as red boxes, which are located in the xlyA gene and nontranscribed DNA sequences, respectively. The xylA start codon is indicated. The lower section shows a comparison of the primary cre +1253 and the putative cre* -10 sequences, which correspond to the degenerated cre motifs. Highly conserved nucleotides are underlined.

图注：BLMA activities and relevant cre structure for B. licheniformis-harboring plasmids. Different versions of mutated cre sequences are classified into two groups, conserved nucleotides and degenerate nucleotides, which are shown in boxes, and mutations are highlighted in red.