该文研究了在MRS培养基中添加0.05 mg/mL LA（Linoleic acid，LA）和不同浓度的乙醇时植物乳杆菌p-8的CLA（Conjugated linoleic acid，CLA）转化率和CLA合成相关酶转录水平的差异情况。结果显示，发酵液中的三种CLA异构体转化率都是在添加0.50%乙醇时最高，其中转化cis9,trans11-CLA（t9,t11-CLA）异构体最高，为2.49%，比不添加乙醇增加2.37倍。添加不同浓度乙醇的发酵液中trans10,cis12-CLA（t10,c12-CLA）转化率都是最低的。菌体中产生的CLA非常少，但规律与发酵液的基本一致。添加0.50%乙醇菌体中t9,t11-CLA转化率最高，其转化率仅为0.05%，比不添加乙醇增加了5倍。当乙醇浓度高于0.50%时，各种不同CLA异构体的转化率却都减少。结果表明CLA是在胞液内产生后再被运转到胞外的，一定浓度范围内的乙醇胁迫通过提高CLA合成相关的酶基因转录水平，进而促进了CLA的转化，可见CLA合成相关酶基因转录水平是造成CLA转化率差异的主要原因。结果为阐明植物乳杆菌p-8产CLA的分子机制和寻找有效提高CLA生成的调控手段奠定了基础。

The effects of the presence of linoleic acid (LA) and ethanol on the conjugated linoleic acid (CLA) conversion rates and the transcription level of CLA synthesis-related enzymes of Lactobacillus plantarum p-8 (L. plantarum p-8) were studied. For this, 0.05 mg/mL LA and ethanol at different concentrations were added to MRS media. The results showed that the conversion rates of the three CLA isomers were the highest when 0.50% ethanol was added to the fermentation broth. More specifically, the conversion rate of the cis9, trans11-CLA (c9,t11-CLA) isomer was the highest, reaching up to 2.49%, which was 2.37 times higher than that observed without ethanol. The conversion rate of the trans10, cis12-CLA (t10,c12-CLA) isomer in the fermentation broth was the lowest, regardless of the concentration of ethanol added. The CLA conversion rates were much higher in the fermentation broths compared to those observed in the bacteria, and the CLA conversion rates in the bacteria were very low, but the variations in the CLA conversion rates following ethanol addition were consistent between the fermentation broths and the bacteria. The conversion rate of the c9,t11-CLA isomer was the highest (0.05%) in the bacteria following 0.50% ethanol treatment. This rate is five times higher than that obtained without ethanol treatment. When the ethanol concentration was higher than 0.50%, the conversion rates of all CLA isomers were reduced. The results indicate that CLA is produced in the cytosol and then transferred to the extracellular environment. Meanwhile, the transcription levels of the genes encoding CLA synthesis-related enzymes increased following ethanol stress within a certain concentration range, and accordingly, the CLA conversion rates increased. It is confirmed that the variation in the transcription levels of the CLA synthesis-related enzyme genes is the main reason for the differences in the CLA conversion rates. The results provide a foundation for elucidating the molecular mechanism of CLA production by Lactobacillus plantarum p-8 and for exploring effective regulation methods to improve CLA production.

国家自然科学基金项目（31560443）；内蒙古自然科学基金项目（2017MS0306）