Characterization of E-type colicinogenic plasmids from Shigella sonnei.
Colicinogenic plasmids encode toxic proteins which have antagonistic activity against closely related bacteria. This study describes the molecular characterization of three colicinogenic plasmids designated as pSSE3, pSSE and pSSE2, each with a molecular size of ∼6 kb, identified in clinical isolates of Shigella sonnei. Sequence analysis revealed that pSSE and pSSE2 shared extensive sequence homology with each other and with Escherichia coli E-type colicinogenic plasmids. The plasmid pSSE3 lacked an additional gene imparting immunity to colicin E8, a unique feature not observed in any of the previously reported sequences of colicin E3 plasmids. Incomplete digestion of colicinogenic plasmids by restriction endonucleases, metachromatic staining with acridine orange and presence of single stranded initiation (ssi) region confirmed the coexistence of ssDNA along with dsDNA. Plasmid copy number as determined by real-time PCR was found to be about 20. Transmission electron microscopy revealed DNA impairment in test bacteria after colicin exposure. We hypothesize that S. sonnei has acquired E-group colicin plasmids from its close relative E. coli, with their sequences undergoing subtle changes depending on the cohabitation in the same milieu.
Division of Bacteriology, National Institute of Cholera and Enteric Diseases, Kolkata-700010, West Bengal, India.
Fatema
F
Calcuttawala
Central Drugs Laboratory, Kolkata-700016, West Bengal, India.
Chellaram
C
Hariharan
National Institute of Pharmaceutical Education and Research, Kolkata-700032, West Bengal, India.
Gururaja P
GP
Pazhani
Division of Bacteriology, National Institute of Cholera and Enteric Diseases, Kolkata-700010, West Bengal, India.
Dhira Rani
DR
Saha
Center for Human Microbial Ecology, Translational Health Science and Technology Institute, Faridabad-121001, Haryana, India.
Thandavarayan
T
Ramamurthy
D003087:Colicins / Q000235:genetics* / Q000494:pharmacology; D004262:DNA Restriction Enzymes / Q000378:metabolism; D004277:DNA, Single-Stranded; D004405:Dysentery, Bacillary / Q000382:microbiology; D004926:Escherichia coli / Q000235:genetics; D046529:Microscopy, Electron, Transmission; D010957:Plasmids; D060888:Real-Time Polymerase Chain Reaction; D012764:Shigella sonnei / Q000187:drug effects / Q000235:genetics* / Q000648:ultrastructure
D003087:Colicins; D004277:DNA, Single-Stranded; D004262:DNA Restriction Enzymes
Escherichia coli; PCN; Shigella sonnei; TEM; colicin; plasmid