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Genetic Regulation of Principal Microorganisms (Yeast, Zymomonas mobilis, and Clostridium thermocellum) Producing Bioethanol/Biofuel
Published in Ayerim Y. Hernández Almanza, Nagamani Balagurusamy, Héctor Ruiz Leza, Cristóbal N. Aguilar, Bioethanol, 2023
Dania Sandoval-Nuñez, Teresa Romero-Gutiérrez, Melchor Arellano-Plaza, Anne Gschaedler, Lorena Amaya-Delgado
Clostridium thermocellum is an anaerobic thermophilic bacterium with a high growth rate on cellulose; this characteristic is due to its highly efficient extracellular free and multienzyme complex termed the cellulosome and its accessory enzymes. A model of the multienzymatic systems is represented in Figure 4.8; some proteins were renamed as follows: CipA (ScaA), OlpB (ScaB), Orf2p (ScaC), OlpA (ScaD), SdbA (ScaF), and OlpC (ScaG) [87]. This enzymatic complex gives C. thermocellum the ability to solubilize the cellulose contained in LCB and rapidly ferment it to produce ethanol. The metabolic ability of C. thermocellum to produce ethanol directly from LCB makes it the main candidate microorganism for bioethanol production via consolidated bioprocessing (CBP). Despite the biotechnological potential of C. thermocellum, the industrial application of this bacterium is relegated because of its disadvantages compared to other microorganisms, such as mixed acid fermentation, low ethanol productivity and titer, low ethanol tolerance, and low hemicellulose utilization [88–90]. To solve these biotechnological limitations, several strategies have been carried out to improve ethanol production by C. thermocellum, from technological strategies such as cocultivation with other bacteria to genomic strategies such as metabolic engineering. In parallel, several genetic and transcriptomic studies have been performed to understand the gene regulation involved in biomass degradation, as well as the ethanol tolerance mechanism used by C. thermocellum [91].
Industrial biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
Clostridium is a genus of Gram-positive bacteria, belonging to the Firmicutes. These are obligate anaerobes capable of producing endospores. Individual cells are rod-shaped, which gives them their name, from the Greek kloster or spindle. These characteristics traditionally defined the genus; however, many species originally classified as Clostridium have been reclassified in other genera. Clostridium thermocellum can utilize lignocellulosic waste and generate ethanol, thus making it a possible candidate for use in ethanol production. It also has no oxygen requirement and is thermophilic, thus reducing cooling cost. Clostridium acetobutylicum, also known as the Weizmann organism, was first used by Chaim Weizmann in 1916 to produce acetone and biobutanol from starch for the production of gunpowder and TNT. The anaerobic bacterium Clostridium ljungdahlii, recently discovered in commercial chicken wastes, can produce ethanol from single-carbon sources, including synthesis gas, a mixture of carbon monoxide and H2 that can be generated from the partial combustion of either fossil fuels or biomass. Use of these bacteria to produce ethanol from synthesis gas has progressed to the pilot plant stage at the BRI Energy facility in Fayetteville, Arkansas. Genes from Clostridium thermocellum have been inserted into transgenic mice to allow the production of endoglucanase. The experiment was intended to learn more about how the digestive capacity of monogastric animals could be improved.
Advancements in Extremozymes and their Potential Applications in Biorefinery
Published in Pratibha Dheeran, Sachin Kumar, Extremophiles, 2022
Among all the biofuels, bioethanol is often regarded as the most promising alternative and additive for gasoline. The production of bioethanol from lignocellulosic biomass includes four main steps: biomass pretreatment, enzymatic hydrolysis, fermentation and distillation (Indira et al. 2018). The production of bioethanol from lignocellulosic raw materials is an ecofriendly approach for sustainable development but the second-generation technology still have problems of high cost, and there are several areas of production technology that still require improvement to cut down the cost (Fig. 13). Because of the unique characteristics, extremophiles are resistant to the adverse conditions involved in bioethanol production and they harbor more advantages than terrestrial microorganisms. In particular, thermophiles and their enzymes have great potential for the bioconversion of lignocellulose into bioethanol. Certain thermophilic bacteria are known to produce both cellulase and xylanase, which can completely hydrolyze biomass at high temperature. For example, treatment of biomass using a thermostable cellulase produced by thermophilic Geobililus sp. R7 has been shown to yield a hydrolysate that was readily fermented by Saccharomyces cerevisiae ATCC 24860T to produce 0.45–0.50 g ethanol/g glucose with a 99% utilization rate of glucose (Zambare et al. 2011). Thermophilic Caldicellulosiruptor bescii and Clostridium thermocellum have been reported for its potential to use cellulose, hemp, as well as pretreated lignocellulosic biomass as a substrate to yield bioethanol. In addition, thermophile Thermoanaerobacterium thermosaccharolyticum M18 is able to directly utilize cellulose and xylan for the production of bioethanol (Ábrego et al. 2017). Although thermophilic bacteria have many advantages and utilize a broad spectrum of degradable carbohydrates and the fermentation of hexose and pentose and offer a low risk of pollution, the problems associated with the low G+C content, the formation of endospores, and the low permeability of plasma membrane increase the difficulty in the genetic engineering of thermophilic bacteria (Jiang et al. 2017).
Recent advances in conventional and genetically modified macroalgal biomass as substrates in bioethanol production: a review
Published in Biofuels, 2023
Priyadharsini P, Dawn SS, Arun J, Alok Ranjan, Jayaprabakar J
Yeast (Saccharomyces cerevisiae) is the most recognized ethanol-producing microbe; it has been used to ferment drinks for thousands of years [71]. Alcoholic fermentation is often performed in anaerobic circumstances. Several modified bacteria and yeast strains have recently been developed to increase bioethanol production from pretreated macroalgal biomass. However, depending on the strain used in the method and the growth kinetics, it may alternate between semi-anaerobic and aerobic modes. Fermentation processes such as simultaneous saccharification and fermentation (SSF) and simultaneous saccharification and co-fermentation (SSCF) have been used to enhance the biological conversion of macroalgal biomass, followed by separate hydrolysis and fermentation (SHF) processes [33]. A bioethanol conversion study using a Gelidium amansii algae strain showed that autoclaving can improve bioethanol production by 76.9% [72]. Table 4 compares several strains of yeast, and the conditions for fermentation and bioethanol production utilizing macroalgal biomass. Currently, bioethanol is manufactured by fermenting different carbohydrate-rich macroalgae at the laboratory scale. Research on the bioconversion of cellulose from the biowaste of maritime macroalgae has demonstrated that pretreatment with hot water followed by Clostridium thermocellum SSF can produce up to 2% bioethanol under optimal conditions [83]. Marine industrial waste macroalgae can thus be exploited to meet future bioenergy needs as an effective source for the production of bioethanol. Figure 5 presents the alcohol fermentation mechanism.
Production of chemicals in thermophilic mixed culture fermentation: mechanism and strategy
Published in Critical Reviews in Environmental Science and Technology, 2020
Kun Dai, Wei Zhang, Raymond Jianxiong Zeng, Fang Zhang
Normally, only simple substrates, such as glucose and xylose, can be directly utilized by thermophiles. However, the more interesting and promising substrates in biomass and municipal sludge cannot be easily utilized and consequently their pretreatment is necessary in TMCF (Khiewwijit, Temmink, Labanda, Rijnaarts, & Keesman, 2015). The chemical methods, including acid-based methods, hydrothermal processing, steam explosion, have been proposed to remove lignin and hemicelluloses in biomass (Fang et al., 2017; Jönsson & Martín, 2016). However, several cellulolytic thermophilic bacteria, including Clostridium thermocellum and Clostridium clariflavum, secrete cellulosomes, and can also degrade the cellulose and hemicellulose into soluble monomers (Artzi, Morag, Barak, Lamed, & Bayer, 2015; Blumer-Schuette et al., 2014). The thermophilic Caldicellulosiruptor spp., such as Caldicellulosiruptor bescii, can even directly degrade the lignocellulosic biomass to H2 and acetate without any pretreatment (Young, Chung, Bomble, Himmel, & Westpheling, 2014).
Current status and future prospects of biological routes to bio-based products using raw materials, wastes, and residues as renewable resources
Published in Critical Reviews in Environmental Science and Technology, 2022
Ji-Young Lee, Sung-Eun Lee, Dong-Woo Lee
LCB provides inexpensive and renewable resources for biotechnological production of biofuels and platform chemicals. However, biomass recalcitrance limits the use of biomass as substrates because it must first be hydrolyzed into fermentable sugars via mechanical or chemical pretreatment before thermochemical or biochemical conversion. To simplify the complex conversion process and minimize costs, CBP has been designed to directly convert LCB into target bio-based products (Brethauer & Studer, 2014; Gowen & Fong, 2011). Unlike conventional biofuel production in which all steps are performed separately, CBP combines enzyme production, polysaccharide hydrolysis, and sugar fermentation into a single-stage operation using single or multiple microorganisms (Figure 2b) (Schuster & Chinn, 2013). A representative example of the implementation of CBP is ethanol production from cellulosic biomass using S. cerevisiae expressing cellulase, but the concept of CBP could be applied for the valorization of other types of biomass (Olson et al., 2012). Despite the use of CBP in industrial processes, quantities of bio-based products from native microorganisms are insufficient to compete with petroleum counterparts. For this purpose, there are three crucial areas in which microorganisms must perform adequately to be effective: product yield to minimize the effects of feedstocks, titer to lower separation costs and decrease the required reactor volumes, and productivity to achieve a rapid rate of production. Thus, microbial platforms for biofuel production should possess the processing capacities for high substrate and high metabolic fluxes, high tolerance to inhibitors and products, and rapid and selective pathways for sugar transport. Advances in metabolic engineering, systems biology, and synthetic biology approaches have facilitated bioprospecting of LCB for high-yield bio-based products using genetically-engineered microorganisms (Gowen & Fong, 2011; Nakamura & Whited, 2003). For instance, Clostridium cellulovorans and Clostridium thermocellum are promising CBP hosts because they can ferment cellulose; engineered pathways in these microorganisms have been successfully used to divert metabolic flux for the enhanced production of butanol and ethanol (Tian et al., 2019; Yang, Xu, et al., 2015). To this end, the use of microbial consortia has been intensively investigated to develop improved CBP technologies for the production of fuels and chemicals from pretreated LCB. Indeed, CBP incorporating aerobic fungi and anaerobic yeast or bacteria has improved the production yields of lactic acid and ethanol by facilitating the utilization of beech wood and wheat straw as biomass (Brethauer & Studer, 2014; Shahab et al., 2018).