乳酸乳球菌Nisin抗性基因nisI的克隆及作为筛选标记的研究

摘要：【目的】为了优化LJ1菌株的培养条件使之产生高活性的胞外褐藻胶裂解酶。【方法】通过富集培养技术从海带筛选到一株褐藻胶裂解酶产生菌LJ1, 依据表型特征、脂肪酸组成分析及16S rRNA基因序列分析对该菌株进行鉴定。通过单因子和正交试验对LJ1 菌株产胞外褐藻胶裂解酶的培养条件进行了优化。【结果】LJ1菌株属于假交替单胞菌属（Pseudoalteromonas）。该菌株产酶的最佳培养基组成为：褐藻胶3 g/L、(NH4)2SO4 3 g/L、NaCl 20 g/L、KH2PO4 0.1 g/L、CaCl2 0.1 g/L；最佳培养条件为：250 mL三角烧瓶中装液量25 mL、接种量3%、摇瓶转速150 r/min、pH7.5、培养温度为28℃、培养时间为24 h。LJ1菌株所产褐藻胶裂解酶的最适温度为40℃，最适pH7.6，最适NaCl浓度为0.3 mol/L。1 mol/L金属离子Mg2+对酶活力有明显的促进作用，而Co2+ 和Zn2+对酶活力有较强的抑制作用。【结论】LJ1菌株是Pseudoalteromonas 新的胞外褐藻胶裂解酶产生菌，在最佳培养条件下，该菌株的酶活力提高了66%。

Cloning of Nisin resistent gene nisI from Lactococcus lactis and its application as a food grade selection marker

Abstract: Objective] To construct an E.coli-L.lactis shuttle expression vector with nisI as a food grade selection marker. Methods] According to the sequence of Nisin resistant gene nisI reported by GenBank, the nisI fragment was amplified by polymerase chain reaction with pLEB590 as template. After being sequenced, the amplicon was confirmed by Blast from NCBI. Then, the nisI was subcloned into the E.coli-L.lactis shuttle vector pMG36e, resulting in the plasmid pMG36e-NisI. The recombinant strain MG1363/pMG36e-NisI was obtained when the plasmid pMG36e-NisI was transformed into L.lactis MG1363 competent cell by electroporation. Results] When the medium contained 20 IU Nisin/mL, the recombinant strain carrying pMG36e-NisI showed the same growth curve and genetic stability as L.lactis MG1363. Conclusion] The nisI gene could be used as a selection marker for construction of a food grade expression vector.