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17 A Postgenomic Overview of the Myxobacteria
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Currently, Myxococcus xanthus is the only species of myxobacteria to mature into the postgenomic phase, and therefore, this chapter focuses on this organism. The chapter begins with a discussion with genomic screens using transposable elements, continues with the paralogous analysis of gene families, and concludes with whole-genome yeast two-hybrid (Y2H) assays. Availability of the M. xanthus genome sequence makes the paralogous characterization of gene families possible. Both of the findings presented in the chapter are significant because they represent how the application of a genome sequence can aid in the identification of genes involved in specific processes such as development and vegetative growth. All of the postgenomics methods presented in the chapter focus on using the genome sequence to facilitate the characterization of genes using experimental techniques. One of the ultimate goals of myxobacterial genomics is to determine the complete set of genetic networks that contribute to the complex life cycle of the myxobacteria. Making sense of these data will require the concerted effort of the whole community of those involved in myxobacterial research to pool resources and share data. Exploratory work using microarrays is currently under way in an effort to identify the temporal expression of genes under a host of different environmental conditions. This work has thus far yielded insight into the number of genes associated with transcriptional activators (TAs) under vegetative conditions.
Schematic of the EPS (eps) region in M. xanthus. A total of 26 ORFs were identified by Lu and coworkers (2005), of which 12 contained Tn5 insertions found through a random mutagenesis screen (indicated by black dots). Reprinted and modified with permission from Lu and coworkers (2005).
Location of magellan-4 insertions in specific regions of the M. xanthus genome. Disruption of putative ORFs resulted in deficiencies in S-motility. Four groups were identified including genes involved in TFP biogenesis (A), EPS biosynthesis (B), and LPS biosynthesis and known S-motility genes (C). Inverted triangles represent magellan-4 insertion sites. Reprinted and modified with permission from Youderian and coworkers (2006).
Domain organization of the 12 FHA-associated NtrC-like activators in M. xanthus. The domain organization of a generic NtrC-like activator is shown for reference. Reprinted with permission from Jelsbak et al., 2005.
Schematic representation of the MrpC pathway. MrpC is found to be regulated using both a two-component signal transduction HPK and an STPK cascade system. Details of this pathway are outlined in the text. Reprinted with permission from Nariya and Inouye (2006).