Department of Animal Science, Biotechnical Faculty, University of Ljubljana, Groblje 3, SI-1230 Domžale, Slovenia.
J Dairy Sci. 2011 Jan;94(1):77-85. doi: 10.3168/jds.2010-3677.
The role of bacteriocins in different environments has not been thoroughly explained, mainly because of the difficulties related to the detection of their production. Nisin, an antimicrobial peptide produced by Lactococcus lactis has a long history of safe use in food products and has been studied from many aspects of genetics, biosynthesis, immunity, regulation, and mode of action. Still, some aspects concerning the dynamics of nisin gene expression remain unknown, especially in complex media like cheese. The main objective of the present study was to quantify in a cheese-like medium the expression of nisin genes in L. lactis M78, a well-characterized nisin A producer isolated from raw milk. The expression of all 11 genes involved in nisin biosynthesis was evaluated during cheese production by real-time reverse transcription-PCR. Total RNA was extracted from cheeses using a direct extraction method without prior separation of microbial cells. The M78 strain grew well in experimental cheeses, producing detectable amounts of nisin after 4 h of fermentation. The presence of nisin as an activator modified both the expression of nisin genes and the accumulation of active nisin. Four groups could be distinguished based on gene expression as a function of time: nisA, nisFEG, nisRK and nisBTCIP. Based on nisin-producing strain growth, nisin activity, function of nisin genes, and their location, correlations were established that contribute to the explanation of regulation of nisin biosynthesis and immunity. This study is the first in which the evolution of bacteriocin gene transcripts has been quantified rigorously in a cheese-like medium.
细菌素在不同环境中的作用尚未得到充分解释，主要是因为其产生的检测存在困难。乳链菌肽是由乳球菌产生的一种抗菌肽，在食品中安全使用已有很长的历史，其在遗传学、生物合成、免疫、调控和作用模式等方面都进行了广泛的研究。然而，关于乳链菌肽基因表达动力学的一些方面仍然未知，特别是在奶酪等复杂培养基中。本研究的主要目的是在类似于奶酪的培养基中定量表达乳链菌 M78 中的乳链菌肽基因，M78 是一种从生牛乳中分离出来的、具有良好特征的乳链菌肽 A 生产菌。通过实时反转录-PCR 评估了奶酪生产过程中参与乳链菌肽生物合成的 11 个基因的表达。使用直接提取方法从奶酪中提取总 RNA，无需事先分离微生物细胞。M78 菌株在实验性奶酪中生长良好，发酵 4 小时后可产生可检测量的乳链菌肽。乳链菌肽作为激活剂的存在既改变了乳链菌肽基因的表达，又积累了活性乳链菌肽。根据基因表达随时间的变化，可以将其分为 4 组：nisA、nisFEG、nisRK 和 nisBTCIP。基于产乳链菌肽菌株的生长、乳链菌肽活性、乳链菌肽基因的功能及其位置，建立了相关性，有助于解释乳链菌肽生物合成和免疫的调控。本研究首次在类似于奶酪的培养基中严格定量了细菌素基因转录物的演变。
