Halophilic archaea and their potential to generate renewable fuels and chemicals

Abstract

Lignocellulosic biofuels and chemicals have great potential to reduce our dependence on fossil fuels and mitigate air pollution by cutting down on greenhouse gas emissions. Chemical, thermal, and enzymatic processes are used to release the sugars from the lignocellulosic biomass for conversion to biofuels. These processes often operate at extreme pH conditions, high salt concentrations, and/or high temperature. These harsh treatments add to the cost of the biofuels, as most known biocatalysts do not operate under these conditions. To increase the economic feasibility of biofuel production, microorganisms that thrive in extreme conditions are considered as ideal resources to generate biofuels and value‐added products. Halophilic archaea (haloarchaea) are isolated from hypersaline ecosystems with high salt concentrations approaching saturation (1.5–5 M salt concentration) including environments with extremes in pH and/or temperature. The unique traits of haloarchaea and their enzymes that enable them to sustain catalytic activity in these environments make them attractive resources for use in bioconversion processes that must occur across a wide range of industrial conditions. Biocatalysts (enzymes) derived from haloarchaea occupy a unique niche in organic solvent, salt‐based, and detergent industries. This review focuses on the use of haloarchaea and their enzymes to develop and improve biofuel production. The review also highlights how haloarchaea produce value‐added products, such as antibiotics, carotenoids, and bioplastic precursors, and can do so using feedstocks considered “too salty” for most microbial processes including wastes from the olive‐mill, shell fish, and biodiesel industries.

Characterization of Polyhydroxybutyrate, PHB, Synthesized by Newly Isolated Haloarchaea Halolamina spp.

“…This versatility could be mainly due to the ability to produce several hydrolytic enzymes such as α-amylases as it has been previously described from other haloarchaea. α-amylases catalyze the hydrolysis of starch and produce fructose and glucose [ 36 , 37 ]. These enzymes were found to be stable under saline concentrations ranging from 2 to 4 M NaCl, while at a concentration of 3 M NaCl, the enzyme exhibited the maximum activity at pH values ranging from 7 to 8 and temperatures between 50 and 60 °C [ 38 ].…”

“…In this regard, two pathways are used by haloarchaea to metabolize the glycerol: On the one hand, glycerol kinase phosphorylates glycerol to synthesize sn-glycerol-3-phosphate (G3P) and then oxidizes it using G3P dehydrogenase (G3PDH) to produce dihydroxyacetone phosphate (DHAP). On the other hand, glycerol can be oxidized using glycerol dehydrogenase to produce dihydroxyacetone (DHA), with the latter being phosphorylated using DHA kinase to DHAP [ 37 ].…”

Industrial Biotechnology Based on Enzymes From Extreme Environments

“…Halophilic extremozymes are used in biocatalysis in non-conventional and organic solvents, either in free or immobilized form. Halophilic cellulases, xylanases and laccases can be used in the production of biofuels and have application in processes where lignocellulose is pretreated with organic solvents or ionic liquids ( Mesbah and Wiegel 2017 ; Amoozegar et al, 2019 ; Kasirajan and Maupin-Furlow 2021 ; Motamedi et al, 2021 ). Free and immobilized lipases from Haloarcula sp.…”

Hypersaline environments as natural sources of microbes with potential applications in biotechnology: The case of solar evaporation systems to produce salt in Alicante County (Spain).

“…These enzymes can play a critical role in the discovery of new renewable energy sources. The use of lignin and cellulose residues presents certain economic limitations, especially in depolymerization processes, due to extreme pH and temperature conditions ( Kasirajan and Maupin-Furlow, 2020 ). Therefore, enzymes obtained from haloarchaea such as Hfx.…”