胚芽乳酸桿菌 (Lactobacillus plantarum) 為廣泛運用於發酵蔬菜與肉類之乳酸菌菌酛。過去之研究指出，多 數胚芽乳酸桿菌帶有單個或多個不同大小之質體。本研究主要針對本土泡菜乳酸菌L. plantarum ATIT-023之最 小無性狀質體pLP-8進行定序與特性分析。DNA定序結果顯示，pLP-8之全長為3,414 bp，GC含量為37.73%。序 列分析結果顯示，此質體帶有三個預測開放讀碼區 (orf1~orf3)，分別可編碼出複製蛋白質、生物功能未知之假 設性蛋白質及移動蛋白質。在orf1 (rep) 上游帶有單股複製起始點與雙股複製起始點，推測此質體為滾輪型複 製質體。即時定量聚合酶連鎖反應結果顯示，此質體在胚芽乳酸桿菌中之複製數為五。未來將進一步利用此 質體中與DNA複製有關之最小區域建構乳酸菌/大腸桿菌穿梭質體，做為胚芽乳酸桿菌基因工程操作之工具。

Lactobacillus plantarum is a lactic acid bacterium widely used as a starter microorganism in vegetable and meat fermentation. Previous studies showed that many L. plantarum strains have one or more native resident plasmids of various sizes. In this study, the smallest cryptic plasmid of L. plantarum ATIT-023 isolated from local pickled cabbage, designated as pLP-8, was sequenced and characterized. Sequencing results showed that pLP-8 consists of 3,414 bp with a GC content of 37.73%. Sequence analysis revealed that pLP-8 contains three putative open reading frames (orf1 to orf3) which could encode proteins designated as a replication protein, a hypothetical protein, and a mobilization protein, respectively. A putative double strand origin and a putative single strand origin were predicted upstream of the orf1 (rep). It is suggested that pLP-8 replicates via the rolling-circle replication mechanism. The relative copy number of pLP-8 was estimated to be about 5 in each cell by real-time quantitative PCR. In the near future, the minimal replicon of pLP-8 will be used for construction of a lactic acid bacteria/Escherichia coli shuttle vector which could be applied as a molecular tool for genetic engineering of L. plantarum.