[Study on the plasmid instability of Bdellovibrio BDG-9]

A new method system was established in this paper to study the plasmid in stability of Bdellovibrio BDG-9. Using this system, it was found that when BDG-9 was cultured singly on the SMB plate, plasmid pST I was unstable although pST I still replicated and distributed to progeny cell normally. The results showed that the pST I copy number in single cell of BDG-9 decreased gradually to zero with the propagation of BDG-9. Additionally, plasmid pST I was very important for the growth of BDG-9, and with the lacking of pST I s, the growth and propagation of BDG-9 ceased.