Differential expression of genes influenced by changing salinity using RNA arbitrarily primed PCR in the archaeal halophile Haloferax volcanii

Extreme halophiles belonging to the domain Archaea require a minimum of approximately 10% NaCl for growth. Many of these obligate halophiles will continue to grow even as NaCl concentrations approach saturation. The haloarchaeon Haloferax volcanii is a model organism in which to study the effects of changes in medium salinity on gene expression, as this organism grows over a wide range of NaCl concentrations, between 12% and 23%, with little effect on growth rate. An RNA arbitrarily primed PCR (RAP-PCR) approach has been applied to identify those genes that are differentially expressed in response to changing salinity. Differences in gene expression can be detected using this methodology, as each sample generates its own unique RNA fingerprint for each growth condition examined. RNA was prepared from H. volcanii cultures grown with two different NaCl concentrations in the medium, RAP-PCR was performed, and seven differentially expressed transcripts were identified. These fragments were cloned, sequenced, and subjected to transcript analysis to confirm their regulation. One of the sequences identified in this study displays homology to the eukaryotic Ser/Thr protein kinase Ire1p, a sensor of protein unfolding in yeast and mammalian cells. Evidence for serine phosphorylation in H. volcanii is also presented.