Molecular Genetics ofArchaea

This chapter discusses molecular genetics of Archaea. Gene transfer systems currently exist for species within all three physiological groups of archaea, halophiles, methanogens, and nonmethanogenic hyperthermophiles. The chapter reviews the development of these systems. Colonization of methanogenic and nonmethanogenic hyperthermophiles on solidified medium is equally problematic, as agar is rapidly dehydrated at high temperatures, especially at the concentrations required for it to remain solidified. Therefore, gellan gum (Gelrite) is used as the solidifying agent for growth of thermophiles and hyperthermophiles, which are incubated in a plastic bag or anaerobe jar to minimize dehydration. Haloarchaea are transformed via polyethylene glycol (PEG) mediated transformation, which was first described in Haloferax volcanii. Gene disruption is required to identify and confirm the function of genes within the archaea. Random mutagenesis using chemical and UV radiation has been successfully used for H. volcanii, Methanococcus voltae, Methanococcus maripaludis, and Pyrococcus abyssi. Progress in the development of methodologies for archaeal genetics has rapidly accelerated in the past decade. Additional methods are currently under development for all three archaeal phyla, including additional systems for markerless exchange, gene expression, topological mapping, protein tagging and expression, as well as others. The choice of archaeal genomes for sequencing is now largely driven by the availability of genetic systems, which at present include complete genomes of the halophiles Haloarcula marismortui and Halobacterium sp.