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MICROBIOLOGY
DNA replication during sporulation in Myxococcus xanthus fruiting bodies
Section of Microbiology and Center for Genetics and Development, University of California, Davis, CA 95616
Communicated by A. Dale Kaiser, Stanford University School of Medicine, Stanford, CA, August 12, 2005 (received for review March 30, 2005)
During the developmental process of the Gram-negative soil bacterium Myxococcus xanthus, vegetatively growing rod cells differentiate to ultimately become metabolically quiescent and environmentally resistant myxospores encased within fruiting bodies. This program, initiated by nutrient deprivation, is propagated by both cell-autonomous and cell-nonautonomous signals. Our goal was to determine whether M. xanthus, like many other developmental systems, uses cell-cycle cues to regulate and control its developmental program. To address this question, the DNA replication cycle was used as a marker to monitor progression through the cell cycle in vegetative, stationary, and developing M. xanthus populations. Using flow cytometry, quantitative fluorescence microscopy, and FISH to establish the chromosome copy number of myxospores, it was determined that vegetatively growing cells contain one to two copies of the genome, but upon entry into stationary phase, the chromosome copy number drops to a single copy. Of particular interest, fruiting body-derived myxospores contain a specific two-chromosome DNA complement with both origin and terminus regions localized to the periphery of the myxospore. We speculate that this duplication of genetic information in the myxospore would help assure viability during germination by providing a second copy of each gene. The results of this study imply that not only is DNA replication tightly regulated during the developmental process of M. xanthus, but that there are also regulatory mechanisms to ensure that all myxospores acquire two copies of the chromosome.
development | chromosome copy number | myxospore
Freely available online through the PNAS open access option.
Abbreviations: FU, fluorescence units; TPM, Tris/MgSO4/KH2PO4.
* To whom correspondence should be addressed. E-mail: mhsinger{at}ucdavis.edu.
© 2005 by The National Academy of Sciences of the USA
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