Recent advances in the production, properties and applications of haloextremozymes protease and lipase from haloarchaea

Proteases and lipases are significant groups of enzymes for commercialization at the global level. Earlier, the industries depended on mesophilic proteases and lipases, which remain nonfunctional under extreme conditions. The discovery of extremophilic microorganisms, especially those belonging to haloarchaea, paved a new reserve of industrially competent extremozymes. Haloarchaea or halophilic archaea are polyextremophiles of domain Archaea that grow at high salinity, elevated temperature, pH range (pH 6-12), and low aw. Interestingly, haloarchaeal proteolytic and lipolytic enzymes also perform their catalytic function in the presence of 4-5 M NaCl in vivo and in vitro. Also, they are of great interest to study due to their capacity to function and are active at elevated temperatures, tolerance to pH extremes, and in non-aqueous media. In recent years, advances have been achieved in various aspects of genomic/molecular expression methods involving homologous and heterologous processes for the overproduction of these extremozymes and their characterization from haloarchaea. A few protease and lipase extremozymes have been successfully expressed in prokaryotic systems, especially E.coli, and enzyme modification techniques have improved the catalytic properties of the recombinant enzymes. Further, in-silico methods are currently applied to elucidate the structural and functional features of salt-stable protease and lipase in haloarchaea. In this review, the production and purification methods, catalytic and biochemical properties and biotechnological applications of haloextremozymes proteases and lipases are summarized along with recent advancements in overproduction and characterization of these enzymes, concluding with the directions for further in-depth research on proteases and lipases from haloarchaea.

Assessment of diversity of archaeal communities in Algerian chott

Halophilic archaea are the dominant type of microorganisms in hypersaline environments. The diversity of halophilic archaea in Zehrez-Chergui (Saharian chott) was analyzed and compared by both analysis of a library of PCR amplified 16S rRNA genes and by cultivation approach. This work, represents the first of its type in Algeria. A total cell count was estimated at 3.8 × 10³ CFU/g. The morphological, biochemical, and physiological characterizations of 45 distinct strains, suggests that all of them might be members of the class Halobacteria. Among stains, 23 were characterized phylogenetically and are related to 6 genera of halophilic archaea.The dominance of the genus Halopiger, has not been reported yet in other hypersaline environments. The 100 clones obtained by the molecular approach, were sequenced, and analyzed. The ribosomal library of 61 OTUs showed that the archaeal diversity included uncultured haloarcheon, Halomicrobium, Natronomonas, Halomicroarcula, Halapricum, Haloarcula, Halosimplex, Haloterrigena, Halolamina, Halorubellus, Halorussus and Halonotius. The results of rarefaction analysis indicated that the analysis of an increasing number of clones would have revealed additional diversity. Surprisingly, no halophilic archaea were not shared between the two approaches. Combining both types of methods was considered the best approach to acquire better information on the characteristics of soil halophilic archaea.

Characterization of a novel halotolerant esterase from Chromohalobacter canadensis isolated from salt well mine

A esterase gene was characterized from a halophilic bacterium Chromohalobacter canadensis which was originally isolated from a salt well mine. Sequence analysis showed that the esterase, named as EstSHJ2, contained active site serine encompassed by a conserved pentapeptide motif (GSSMG). The EstSHJ2 was classified into a new lipase/esterase family by phylogenetic association analysis. Molecular weight of EstSHJ2 was 26 kDa and the preferred substrate was p-NP butyrate. The EstSHJ2 exhibited a maximum activity at 2.5 M NaCl concentration. Intriguingly, the optimum temperature, pH and stability of EstSHJ2 were related to NaCl concentration. At 2.5 M NaCl concentration, the optimum temperature and pH of EstSHJ2 were 65 ℃ and pH 9.0, and enzyme remained 81% active after 80 ℃ treatment for 2 h. Additionally, the EstSHJ2 showed strong tolerance to metal ions and organic solvents. Among these, 10 mM K⁺, Ca²⁺ , Mg²⁺ and 30% hexane, benzene, toluene has significantly improved activity of EstSHJ2. The EstSHJ2 was the first reported esterase from Chromohalobacter canadensis, and may carry considerable potential for industrial applications under extreme conditions.

Extracellular hydrolytic enzymes produced by halophilic bacteria and archaea isolated from hypersaline lake

The screening of bacteria and archaea from Chott El Jerid, a hypersaline lake in the south of Tunisia, led to the isolation of 68 extremely halophilic prokaryotes growing in media with 15-25% of salt. Assessment of 68 partial 16S rRNA analyzed by amplified rDNA restriction analysis (ARDRA) revealed 15 different bacterial and archaeal taxonomic groups. Based on ARDRA results, phenotypic and hydrolytic activity tests, 20 archaeal and 6 bacterial isolates were selected for sequencing. The halophilic isolates were identified as members of the genera: Salicola, Bacillus, Halorubrum, Natrinema and Haloterrigena. Most of these isolates are able to produce hydrolytic enzymes such as amylase, protease, lipase, cellulase, xylanase, pectinase and some of them showed combined activities. Natrinema genus is an excellent candidate for lipase production. These results indicated that the extremely halophilic archaea and bacteria from Chott El Jerid are a potential source of hydrolytic enzymes and may possess commercial value.

Solid-state fermentation as a potential technique for esterase/lipase production by halophilic archaea

Halophilic archaea are extremophiles, adapted to high-salt environments, showing a big biotechnological potential as enzyme, lipids and pigments producers. Four inert supports (perlite, vermiculite, polyurethane foam and glass fiber) were employed for solid-state fermentation (SSF) of the halophilic archaeon Natronococcus sp. TC6 to investigate biomass and esterase production. A very low esterase activity and high water activity were observed when perlite, vermiculite and polyurethane were used as supports. When glass fiber was employed, an important moisture loss was observed (8.6%). Moreover, moisture retention was improved by mixing polyurethane and glass fiber, resulting in maximal biomass and esterase production. Three halophilic archaea: Natronococcus sp. TC6, Halobacterium sp. NRC-1 and Haloarcula marismortui were cultured by submerged fermentation (SmF) and by SSF; an improvement of 1.3- to 6.2-fold was observed in the biomass and esterase production when SSF was used. Growth was not homogeneous in the mixture, but was predominant in the glass fiber thus was probably because the glass fiber provides a holder to the cells, while the polyurethane acts as an impregnation medium reservoir. To the best of our knowledge, this work is the first report on haloarchaea cultivation by SSF aiming biomass and esterase/lipase activity production.