HMG-CoA reductase is regulated by salinity at the level of transcription in Haloferax volcanii

Abstract

The moderately halophilic archaeon Haloferax volcanii was surveyed for protein profile changes correlated with growth at high and low salinity. A single polypeptide with an approximate mass of 46 kDa was conspicuously more abundant during growth at high salinity. This protein was identified as HMG-CoA reductase (HMGR), encoded by the hmgR gene. HMGR is a key enzyme in the mevalonate pathway of isoprenoid biosynthesis, the sole route in haloarchaea for lipid and carotenoid production. Enzymatic assays confirmed that HMGR activity is more abundant in cells grown at high salinity. Low salt cultures of H. volcanii contained lower amounts of hmgR transcript compared to cells grown in high salt suggesting that the observed regulation occurs at the level of transcription. Paradoxically, both lipid and carotenoid content decreased in H. volcanii grown at high salinity despite the increased levels of HMGR specific activity. To our knowledge, this is the first report demonstrating that the expression of HMGR is regulated in response to non-optimal salinity in a halophilic archaeon.

Proteomic analysis of Haloferax volcanii reveals salinity-mediated regulation of the stress response protein PspA

“…The proteins identified as more abundant in high-versus optimal-salt medium included homologues of translation elongation factor 1a (EF1a), a regulatory subunit of acetolactate synthase (IlvN-like protein) and a transcriptional regulator related to the phage shock protein PspA. Not listed in Table 1 is HMG CoA reductase, which was found to display an approximately fourfold increase in expression under high-salt growth conditions, corroborating our previous findings (Bidle et al, 2007). It is also noteworthy that a recent survey of H. volcanii genes regulated by non-optimal high salinity via microarray analysis detected similar patterns of regulation compared with this proteomic analysis (C. Daniels, personal communication).…”

“…Haloferax volcanii is a model haloarchaeon that grows optimally in environments containing 2-2.5 M NaCl, but is capable of growth in salinities ranging from 1.5 to 4 M NaCl (Mullakhanbhai & Larsen, 1975). Both salinity-mediated gene regulation, and protein expression and activity have been examined in H. volcanii (Bidle, 2003;Bidle et al, 2007;Daniels et al, 1984;Ferrer et al, 1996;Mojica et al, 1997), although many of the precise genetic mechanisms involved in these adaptations await further investigation.…”

Transcriptional profiling of the model Archaeon Halobacteriumsp. NRC-1: responses to changes in salinity and temperature

“…The long-chain fatty acid-CoA ligase, coded by lfl 3, was up-regulated 2.1-fold in high salt. However, we did not observe a similar change in other genes involved in lipid metabolism [35]. The glutamine synthetase gene, gln A, was down-regulated (1.7-fold) under low salt conditions.…”

Transcription of the three HMG-CoA reductase genes of Mucor circinelloides

“…Previously, HmgR activity and protein level were found to be essential for the adaptation of certain fungi to the changing salinity of the environment [8,22]. Thus, we examined whether salt stress has any effect on the transcription of the hmgR genes of M. circinelloides .…”