Characterization of three cryptic plasmids from Lactobacillus plantarum G63 that was isolated from Chinese pickle

• The pG6302 replicate via theta mechanism and have a novel replicon.
• pG6303 was thought to replicate via a completely new mechanism.
• All the orfs of three plasmids were annotated and carried functional analysis.

Three plasmids from Lactobacillus plantarum G63, pG6301, pG6302 and pG6303, were sequenced and have molecular sizes of 3516-bp, 9112-bp and 10047-bp, respectively. We determined the replicons of these plasmids. The pG6301 plasmid carried a replication gene that functioned by the rolling-circle replication mechanism. The Rep protein of pG6302 shared extremely low similarity with a reported plasmid, pLME300, which replicated by a bi-directional mechanism. Both the Rep protein and OriV analyses indicated a similar replication mechanism in pG6302. Conversely, we found neither the Rep protein nor OriV when we analyzed the whole sequence of pG6303. This finding may illustrate a novel replication mechanism. Additionally, the transposon, a mobilization element, was analyzed and compared to a similar insertion sequence (IS) element. A predicted lysozyme gene, pG6303 guhA, was heterologously expressed, but no activity was detected. The pG6302 and pG6303 plasmids contain new replicons and may be useful vector candidates for future molecular manipulation of L. plantarum.