Biorefinery Gets Hot: Thermophilic Enzymes and Microorganisms for Second-Generation Bioethanol Production

Abstract

To mitigate the current global energy and the environmental crisis, biofuels such as bioethanol have progressively gained attention from both scientific and industrial perspectives. However, at present, commercialized bioethanol is mainly derived from edible crops, thus raising serious concerns given its competition with feed production. For this reason, lignocellulosic biomasses (LCBs) have been recognized as important alternatives for bioethanol production. Because LCBs supply is sustainable, abundant, widespread, and cheap, LCBs-derived bioethanol currently represents one of the most viable solutions to meet the global demand for liquid fuel. However, the cost-effective conversion of LCBs into ethanol remains a challenge and its implementation has been hampered by several bottlenecks that must still be tackled. Among other factors related to the challenging and variable nature of LCBs, we highlight: (i) energy-demanding pretreatments, (ii) expensive hydrolytic enzyme blends, and (iii) the need for microorganisms that can ferment mixed sugars. In this regard, thermophiles represent valuable tools to overcome some of these limitations. Thus, the aim of this review is to provide an overview of the state-of-the-art technologies involved, such as the use of thermophilic enzymes and microorganisms in industrial-relevant conditions, and to propose possible means to implement thermophiles into second-generation ethanol biorefineries that are already in operation.

Polyphasic Analysis Reveals Potential Petroleum Hydrocarbon Degradation and Biosurfactant Production by Rare Biosphere Thermophilic Bacteria From Deception Island, an Active Antarctic Volcano

“…Discovery and study of new microorganisms, particularly thermophiles, from this extreme continent are important not only for the contribution to knowledge of microbial ecology and biodiversity but as a source of novel biocompounds with potential uses for industrial, environmental, medical, and commercial purposes ( Perfumo et al, 2018 ). Because of their thermal and chemical stability as well as structural and molecular modifications, thermophiles can be used for processes that require high temperatures, such as in the bioenergy, bioconversion, pharmaceutical, biomedical, detergent, agriculture, and oil industries ( Schultz and Rosado, 2020 ; Zuliani et al, 2021 ). In the oil industry, thermophiles have received increasing attention for two main applications: microbial enhanced oil recovery (MEOR), a tertiary oil recovery technique ( Datta et al, 2022 ), and bioremediation of extreme environments contaminated by crude oil and its derivatives ( Almeida et al, 2016 ; Schultz and Rosado, 2020 ).…”

Comparative analysis reveals distinctive genomic features of Taiwan hot-spring cyanobacterium Thermosynechococcus sp. TA-1

“…The information would be valuable for developing feasible solutions to mitigate the impacts of global warming ( Matos et al, 2021 ). Additionally, the thermostable enzymes and bioproducts of these bacteria have been utilized in numerous scientific research and biotechnology applications ( Leu et al, 2013 ; Su et al, 2013 ; Liang et al, 2019 ; Patel et al, 2019 ; Zuliani et al, 2021 ), which further illustrates the importance of these organisms.…”

Biotechnological Prospects of Thermoanerobacter AK15: End-Product Formation from Carbohydrates, Amino Acids, and Lignocellulosic and Macroalgae Hydrolysates

“…In all cases, the grass hydrolysates were pretreated with acid, as well as with enzymatic pretreatment, as performed in the present study. Many other reports on thermophiles capable of good ethanol yields from lignocellulose have also been presented in recent years [ 30 , 43 , 44 , 45 , 46 ]. Thus, Thermoanaerobacter strain AK15 seems to be suitable for bioethanol production from complex biomass with good ethanol yields.…”