SH1, a halophilic virus of Archaea; Genetics and Evolution

Little is known about the biodiversity and metabolism of microbes living in extreme habitats, the enviroments of many Archaea, yet such cells offer a relatively untapped source of enzymes for biotechnological use. The most intensively studied Archaea are the extreme thermophiles, as evidenced by the many commercially produced archaeal DNA polymerases used in PCR. Extremely halophilic archaea are the dominant members of hypersaline environments, such as salt lakes, and are adapted to grow at 3-5 molar salt concentrations. Here also are high concentrations of viruses (haloviruses) that, like their counterparts in marine waters, are believed to play major roles in limiting host cell populations (and the corresponding metabolic activities), recycling cell nutrients (via cell lysis), driving host cell evolution, and in lateral gene transfer. There appear to be many novel virus types, and their biotechnological potential is also significant, such as enzymes (e.g. polymerases), and replication genes and regulatory elements that could be used to construct genetic tools for high-level expression of haloarchaeal proteins. Because of their small genomes and precisely controlled programs of gene expression, archaeal viruses offer robust systems for genetic study, and will be useful for developing genetic tools to express halophilic enzymes (similar to the tools developed from bacteriophage research). They can also shed light on the movement of genes between host cells, an area gaining increasing attention with genomic and metagenomic sequence studies of various microbes and their environments. The proposal will focus on a representative halovirus, SH1, a 70 nm diameter, round virus that is a dominant morphotype in hypersaline waters. The basic virological characteristics, infection cycle and genome sequence have been recently published. It is able to infect species belonging to two genera of halobacteria, and the purified DNA genome of SH1 can transfect a much wider variety of cells. The aims of this project are: a) To understand the mechanisms of gene expression and regulation in the halophilic virus SH1. b) To develop methods for genetic engineering of haloviruses in order to study their structure and functional organization. c) To understand how the archaeal virus SH1 can replicate in such a wide range of cell types. The Dyall-Smith laboratory has developed tools to assess haloarchaeal promoter strengths, including halovirus promoters, and has mapped the major transcripts of SH1 (Kate Porter, unpublished). The project is well-timed to take advantage of these techniques and data to gain a detailed insight into the molecular biology of this virus.