The LonB protease controls membrane lipids composition and is essential for viability in the extremophilic haloarchaeon Haloferax volcanii

Abstract

Although homologs of the ATP-dependent Lon protease exist in all domains of life, the relevance of this protease in archaeal physiology remains a mystery. In this study, we have constructed and phenotypically characterized deletion and conditional lon mutants in the model haloarchaeon Haloferax volcanii to elucidate the role of the unusual membrane-bound LonB protease in archaea. Hvlon could be deleted from the chromosome only when a copy of the wild type gene was provided in trans suggesting that Lon is essential for survival in this archaeon. Successful complementation of the lethal phenotype of ΔHvlon was attained by expression of the heterologous protease gene Nmlon from the haloalkaliphilic archaeon Natrialba magadii, meaning that the biological function of Lon is conserved in these organisms. Suboptimal cellular levels of Lon protein affected growth rate, cell shape, cell pigmentation, lipid composition and sensitivity to various antibiotics. The contents of bacterioruberins and some polar lipids were increased in the lon mutants suggesting that Lon is linked to maintenance of membrane lipid balance which likely affects cell viability in this archaeon. The phenotypes associated to a membrane-bound LonB protease mutant were examined for the first time providing insight on the relevance of this protease in archaeal physiology.

Bacterioruberin extracts from a genetically modified hyperpigmented Haloferax volcanii strain: antioxidant activity and bioactive properties on sperm cells

“…We have previously shown that HVLON3 produces higher Bctr amounts (10–15 fold) than the parental strain (H26) as estimated in relative units (Cerletti et al . ). In this work, we determined the Bctr content per biomass units (mg g −1 cell dry weight, DW) which on average was 13·8 ± 2·3 mg g −1 cell DW for H26 and 219·8 ± 13 mg g −1 cell DW for HVLON3, in agreement with our initial observation.…”

“…In our laboratory, we have previously constructed a genetically modified strain of the model haloarchaeon Haloferax volcanii (HVLON3) with a genetic modification in the carotenoid biosynthesis pathway which synthesizes higher levels of carotenoids (Bctr) compared to the wt (Cerletti et al . ).…”

“…To advance in knowledge on the bioactive properties of Bctr as well as to implement their biotechnological and biomedical applications it is central to have a suitable biological resource with high capability of Bctr production. In our laboratory, we have previously constructed a genetically modified strain of the model haloarchaeon Haloferax volcanii (HVLON3) with a genetic modification in the carotenoid biosynthesis pathway which synthesizes higher levels of carotenoids (Bctr) compared to the wt (Cerletti et al 2014).…”

Archaeal membrane-associated proteases: insights on Haloferax volcanii and other haloarchaea

“…As FtsH is for Escherichia coli (Langklotz et al, 2012), LonB is essential for viability of H. volcanii cells. On the other hand suboptimal expression of this protease affects growth rate, cell shape, antibiotic sensitivity, and lipid composition (Cerletti et al, 2014). Also, H. volcanii mutant cells deficient in Lon content are more sensitive to puromycin compared to wild type cells suggesting that LonB is involved in the disposal of abnormal proteins.…”

“…A distinctive feature of haloarchaea is the presence of red membrane-bound carotenoid pigments (C50-bacterioruberins) which serve to protect their macromolecules from the damaging effects of UV light (Khanafari et al, 2010). Interestingly, the cellular content of bacterioruberins dramatically increased in H. volcanii mutant cells with a suboptimal Lon concentration while overexpression of this protease rendered the cells colorless (Cerletti et al, 2014). This observation suggests that LonB controls carotenoid biosynthesis in H. volcanii probably by degrading enzyme/s involved in this pathway.…”