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Molecular Biology of Thermophilic and Psychrophilic Archaea
Published in Ajar Nath Yadav, Ali Asghar Rastegari, Neelam Yadav, Microbiomes of Extreme Environments, 2021
Chaitali Ghosh, Jitendra Singh Rathore
Apart from the above mentioned methods, Horizontal Gene Transfer (HGT) is also an important process for thermophiles. For example the genome of Thermomicrobium roseum DSM 5159 have a circular chromosome (2.0 Mbp) and one megaplasmid (919,596 bp) (Wu et al. 2009). The gene encoding flagellar system is generally encoded by the genome. Interestingly in this bacterium, it is located in the megaplasmid and not in the bacterial chromosome. In another example, Thermotoga maritima are able to adapt to high temperatures because 24% of its genes are acquired from archaea (Nelson et al. 1999; Zhaxybayeva et al. 2009). Therefore, from the above findings it has been established that horizontal gene transfer work as a survival mechanism under extreme conditions (Goh et al. 2014).
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
It is known that H2 production is the key to control the intercellular redox reactions (Bastidas-Oyanedel et al., 2012; Regueira et al., 2018). As shown in Table 2, NADH and Fdred are produced together with the metabolites of acetate and butyrate. Thus, to balance the intercellular redox reactions, various kinds of hydrogenases reduce H+ to produce H2 or produce ethanol and propionate. The production of H2 is controlled via four pathways by the redox couples of NADH/NAD+ and Fdred/Fdox, and formate (Pawar & Niel, 2013; Schut & Adams, 2009; Stephen, Archer, Orozco, & Macaskie, 2017), as shown in Figure 3. First, due to the thermophilic inhibition of NADH/NAD+ (−320 mV), the reaction in Equation (4) occurs only when the PH2 is below 60 Pa. Second, since the potential of Fdred/Fdox (< −400 mV) is closed to that of H2/H+ (−414 mV), it is the more suitable electron donor for H2 production, especially in TMCF (Equation (5)). Third, H2 can also be produced from formate (Equation (6)), in which the ratio of H2 verse (H2 + formate) is found to be thermodynamically controlled in TMCF (Zhang, Chen, Dai, Shen, & Zeng, 2015). The fourth pathway, reported by Schut and Adams (2009), involves a [FeFe] hydrogenase in the hyperthermophilic bacterium of Thermotoga maritima, which can simultaneously utilize NADH and ferredoxin as electron donors to produce H2 (Equation (7)).
Production of cellulases by Aureobasidium pullulans LB83: optimization, characterization, and hydrolytic potential for the production of cellulosic sugars
Published in Preparative Biochemistry & Biotechnology, 2021
Matheus Maitan Vieira, Elen Kadoguchi, Fernando Segato, Silvio S. da Silva, Anuj K. Chandel
Enzymatic activities (CMC and FPU activity) of crude enzyme extract (CEE) from A. pullulans after growing using the optimized set of conditions. Table 2 shows the enzyme activity profile of A. pullulans. The substrates used were pNP-α-L-arabinofuranoside (pNP-A), pNP-β-D-cellobioside (pNP-C), pNP-β-D-glucoside (pNP-G) and pNP-β-D-xylopyranoside (pNP-X). The results show a higher activity when using pNP-G as substrate, with an average activity of 6.11 U/mL, higher than the other substrates. This may be explained by the fact that β-glucosidase is generally responsible for regulating the entire cellulolytic process and is a rate-limiting factor during cellulose enzymatic hydrolysis, as endoglucanase and exoglucanase activities are often inhibited by cellobiose.[3,5] Another important factor is that activity of pNP-C was 1.33 U/mL, lower than pNP-G, which is due to β-glucosidase not only producing glucose from cellobiose, but also reduce inhibition of cellobiose, allowing production of endoglucanase, and exoglucanase more efficiently.[15] Schneider et al.[34] analyzed the enzymatic activity produced from Penicillium echinulatum from wild (2HH) and mutant (S1M29) strains grown on four feedstocks, i.e. steam-exploded sugarcane bagasse, cellulose, glycerol, and glucose. This study showed different results as the pNPG activity was not detectable. The other enzyme for example pNPC, pNPX, and pNPA activities were found. Bronnenmeier et al.[35] studied the auxiliary enzymes production by Thermotoga maritima grown on xylan as substrate and obtained specific enzyme activity of 40.70 mU/mg protein for pNPX, much higher than the other substrates (pNPG, pNPC, and pNPA), which is due to the fact that xylan being the main substrate, causing the microorganism to have few carbon source options, producing more degrading enzymes of such substrate. Moreover, they obtained a higher enzymatic activity on pNPG substrate than pNPC, which can also be explained by the fact that β-glucosidase is responsible for regulating the cellulolytic process and reducing the action of cellobiose.[15] Enzyme production directly depends on the type of microorganisms used, supplied carbon, and nitrogen sources, cultivation conditions, among others. For instance, Yanjun et al.[36] cultivated A. pullulans 98 on enriched media (carboxymethyl cellulose, 20 g/L; yeast extract, 20 g/L; peptone, 5 g/L) and found the specific activity of CMCase (4.51 U/mg protein). Later, Kudanga and Mwenje[37] reported endoglucanase specific activities from 2.37 to 12.88 µmol glucose/mg protein/h and exoglucanase activities from 0.293 to 22.442 µmol glucose/mg protein/day by various isolates of A. pullulans from the temperate regions.