This Article Full Text Full Text (PDF) Other Versions of this Article: JB.00602-08v1 190/17/5934    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Google Scholar Articles by Raghavan, R. Articles by Minnick, M. F. PubMed PubMed Citation Articles by Raghavan, R. Articles by Minnick, M. F.

 Previous Article  |  Next Article 

Journal of Bacteriology, September 2008, p. 5934-5943, Vol. 190, No. 17
0021-9193/08/$08.00+0     doi:10.1128/JB.00602-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Toxic Introns and Parasitic Intein in Coxiella burnetii: Legacies of a Promiscuous Past

Division of Biological Sciences, The University of Montana, Missoula, Montana 59812

Received 30 April 2008/ Accepted 19 June 2008

The genome of the obligate intracellular pathogen Coxiella burnetii contains a large number of selfish genetic elements, including two group I introns (Cbu.L1917 and Cbu.L1951) and an intervening sequence that interrupts the 23S rRNA gene, an intein (Cbu.DnaB) within dnaB and 29 insertion sequences. Here, we describe the ability of the intron-encoded RNAs (ribozymes) to retard bacterial growth rate (toxicity) and examine the functionality and phylogenetic history of Cbu.DnaB. When expressed in Escherichia coli, both introns repressed growth, with Cbu.L1917 being more inhibitory. Both ribozymes were found to associate with ribosomes of Coxiella and E. coli. In addition, ribozymes significantly reduced in vitro luciferase translation, again with Cbu.L1917 being more inhibitory. We analyzed the relative quantities of ribozymes and genomes throughout a 14-day growth cycle of C. burnetii and found that they were inversely correlated, suggesting that the ribozymes have a negative effect on Coxiella's growth. We determined possible sites for ribozyme associations with 23S rRNA that could explain the observed toxicities. Further research is needed to determine whether the introns are being positively selected because they promote bacterial persistence or whether they were fixed in the population due to genetic drift. The intein, Cbu.DnaB, is able to self-splice, leaving the host protein intact and presumably functional. Similar inteins have been found in two extremophilic bacteria (Alkalilimnicola ehrlichei and Halorhodospira halophila) that are distantly related to Coxiella, making it difficult to determine whether the intein was acquired by horizontal gene transfer or was vertically inherited from a common ancestor.

Published ahead of print on 7 July 2008.