A bioluminescent reporter for the halophilic archaeon Haloferax volcanii

Improving the genetic system for Halorubrum lacusprofundi to allow in-frame deletions

Halorubrum lacusprofundi is a cold-adapted halophilic archaeon isolated from Deep Lake, Antarctica. Hrr. lacusprofundi is commonly used to study adaptation to cold environments and thereby a potential source for biotechnological products. Additionally, in contrast to other haloarchaeal model organisms, Hrr. lacusprofundi is also susceptible to a range of different viruses and virus-like elements, making it a great model to study virus-host interactions in a cold-adapted organism. A genetic system has previously been reported for Hrr. lacusprofundi; however, it does not allow in-frame deletions and multiple gene knockouts. Here, we report the successful generation of uracil auxotrophic (pyrE2) mutants of two strains of Hrr. lacusprofundi. Subsequently, we attempted to generate knockout mutants using the auxotrophic marker for selection. However, surprisingly, only the combination of the auxotrophic marker and antibiotic selection allowed the timely and clean in-frame deletion of a target gene. Finally, we show that vectors established for the model organism Haloferax volcanii are deployable for genetic manipulation of Hrr. lacusprofundi, allowing the use of the portfolio of genetic tools available for H. volcanii in Hrr. lacusprofundi.

Progress and Challenges in Archaeal Genetic Manipulation

Archaea inhabit a wide variety of habitats and are well-placed to provide insights into the origins of eukaryotes. In this primer, we examine the available model archaeal genetic systems. We consider the limitations and barriers involved in genetically modifying different archaeal species, the techniques and breakthroughs that have contributed to their tractability, and potential areas for future development.

High-level synthesis and secretion of laccase, a metalloenzyme biocatalyst, by the halophilic archaeon Haloferax volcanii

Haloarchaea and their enzymes have extremophilic properties desirable for use as platform organisms and biocatalysts in the bioindustry. These GRAS (generally regarded as safe) designated microbes thrive in hypersaline environments and use a salt-in strategy to maintain osmotic homeostasis. This unusual strategy has resulted in the evolution of most of the intracellular and extracellular enzymes of haloarchaea to be active and stable not only in high salt (2-5M) but also in low salt (0.2M). This salt tolerance is correlated with a resilience to low water activity, thus, rendering the haloarchaeal enzymes active and stable in organic solvent and temperatures of 50-60°C used in the enzymatic biodelignification and saccharification of lignocellulosic materials. High-level secretion of haloarchaeal enzymes to the extracellular milieu is useful for many applications, including enzymes that deconstruct biomass to allow for lignin depolymerization and simultaneous fermentation of sugars released from hemicellulose and cellulose fractions of lignocellulosics. Here we detail strategies and methods useful for high-level secretion of a laccase, HvLccA, that mediates oxidation of various phenolics by engineering a recombinant strain of the haloarchaeon Haloferax volcanii.

Mutant firefly luciferase enzymes resistant to the inhibition by sodium chloride

OBJECTIVES

Firefly luciferase, one of the most extensively studied enzymes, has numerous applications. However, luciferase activity is inhibited by sodium chloride. This study was aimed at obtaining mutant luciferase enzymes resistant to the sodium chloride inhibition.

RESULTS

We first obtained two mutant luciferase enzymes whose inhibition were alleviated and determined the mutations to be Val288Ile and Glu488Val. Under medical dialysis condition (140 mM sodium chloride), the wild type was inhibited to 44% of its original activity level. In contrast, the single mutants, Val288Ile and Glu488Val, retained 67% and 79% of their original activity, respectively. Next, we introduced Val288Ile and Glu488Val mutations into wild-type luciferase to create a double mutant using site-directed mutagenesis. Notably, the double mutant retained its activity more than 95% of that in the absence of sodium chloride.

CONCLUSIONS

The mutant luciferase, named luciferase CR, was found to retain its activity in various concentrations of sodium chloride. The luciferase CR may be extensively useful in any bioassay which includes firefly luciferase and is employed in the presence of sodium chloride.

Haloferax volcanii-a model archaeon for studying DNA replication and repair

The tree of life shows the relationship between all organisms based on their common ancestry. Until 1977, it comprised two major branches: prokaryotes and eukaryotes. Work by Carl Woese and other microbiologists led to the recategorization of prokaryotes and the proposal of three primary domains: Eukarya, Bacteria and Archaea. Microbiological, genetic and biochemical techniques were then needed to study the third domain of life. Haloferax volcanii, a halophilic species belonging to the phylum Euryarchaeota, has provided many useful tools to study Archaea, including easy culturing methods, genetic manipulation and phenotypic screening. This review will focus on DNA replication and DNA repair pathways in H. volcanii, how this work has advanced our knowledge of archaeal cellular biology, and how it may deepen our understanding of bacterial and eukaryotic processes.