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Normalization of Capp-Switch reads enhances TSS identification for C. beijerinckii DSM 6423. (a) TSS expression distribution with (normalized) and without (raw) expression normalization (10 reads per million [RPM] [TSS] detection threshold shown). (b) RNA-seq expression distributions of (i) all genes (black line) and (ii) the subset of genes for which TSSs have been found, in normalized (blue) and raw (red) data sets (25 RPM detection threshold shown). (c) Number of TSSs found for normalized and raw data sets. (d) TSS number per gene (with detected TSSs, 25 RPM detection threshold shown). Value corresponds to the number of reads falling in each category (as percentage of the total RPM). (e) Venn diagram showing TSSs found for each data set (25 RPM detection threshold shown) and the corresponding numbers of associated genes.
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Innovative processes to transform plant biomass into renewable chemicals are needed to replace fossil fuels and limit climate change. Clostridium acetobutylicum is of industrial interest because it ferments sugars into acetone, butanol and ethanol (ABE). However, this organism is unable to depolymerize cellulose, limiting its use for the direct tra...
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... According to Fig. 4b, to the higher volume of Clac in the inoculum, the higher was the BioH 2 production. Although several anaerobic species of Clostridium can hydrolyze cellulose through the cellulosome secretion, Clac secretes very small quantities of this multi-enzyme complex, therefore, it is only considered a solventogenic strain [57]. Fig. 4c, shows that the lowest pH value (5.5) favored the production of BioH 2 (331.6 mL), thus the increase of pH from 6.5 to 7.5 decreased the gas production. ...
Bovine ruminal fluid (BRF) bioaugmented with Clostridium acetobutylicum (Clac) was assessed for hydrolyzing cellulose and produce biohydrogen (BioH2) simultaneously from pretreated corncob in a single step, without the use of external hydrolytic biocatalysts. The corncob was pretreated using three thermochemical methods: H2SO4 2%, 160 °C; NaOH 2%, 140 °C; NaOCl 2%, 140 °C; autohydrolysis: H2O, 190 °C. Subsequently, BioH2 production was carried out using the pretreated material with the highest digestibility applying a Taguchi experimental array to identify the optimal operating conditions. The results showed a higher glucose released from pretreated corncob with H2SO4 (134.7 g/L) compared to pretreated materials by autohydrolysis, NaOH and NaOCl (123 g/L, 89.8 g/L and 52.9 g/L, respectively). The mixed culture was able to hydrolyze the pretreated corncob and produce 575 mL of H2 (at 35 °C, pH 5.5, 1:2 ratio of BRF:Clac and 5% of solids loading) equivalent to 132 L H2/Kg of biomass.
... Several methods including, the chemical pretreatment, employing commercial enzyme on saccharification, co- culture of two bacterial strain, and simultaneous saccharification by Clostridium are applied to overcome the barrier for releasing fermentable sugar (Table 2). However, previous studies related to saccharification by Clostridium showed the low-solvent yield due to the weak amylase enzyme activity of Clostridia [34,35]. Additionally, in a study by Tran et al., the co-culture of Bacillus subtilis and Clostridium butylicum TISTR 1032 was reported that the highest ABE concentration was measured at 7.40 g/l from 40 g/l starch, which was a 2-fold less than the two-step fermentation [18]. ...
In Asia, uneaten cooked rice is the highest portion amongst many forms of food wastes that are thrown away. In order to make use of the thrown-away rice and potentially use it for liquid fuels, steamed Japanese rice was evaluated on biobutanol production through a two-step fermentation by amylase-producing Aspergillus oryzae, and solvent-producing Clostridium acetobutylicum YM1. The effects of sterilization and providing anaerobic conditions on solvent production in acetone-butanol-ethanol (ABE) fermentation cannot be underestimated. Several conditions, including aerobic, anaerobic, sterile, and non-sterile were investigated concerning the solvent production capability of Clostridium acetobutylicum YM1. The maximum solvent production was 11.02 ± 0.22 g/l butanol and 18.03 ± 0.34 g/l total ABE from 75 g/l dried rice. The results confirmed that the solvent production performance of the YM1 strain was not affected by the sterilization conditions. In particular, 10.91 ± 0.16 g/l butanol and 16.68 ± 0.22 g/l ABE were produced under non-sterile and aerobic conditions, which can reduce industrial-scale production costs.
In the quest for identifying novel renewable energy sources, higher alcohols from fermentative processes have received enormous interest in the last decades. Commercial microbial butanol production through the traditional acetone-butanol-ethanol process was common in the first half of the 20th century, and many attempts are underway to revive this process for butanol production. In addition to butanol, other linear and branched higher alcohols hold great promise as alternative energy sources. Although Clostridium species can naturally produce butanol, most of the other higher alcohols are synthesized in nonnative hosts. This requires the construction of novel pathways, the introduction of heterologous genes, and extensive genetic manipulation of host strains. Therefore, this chapter aims to demonstrate metabolic pathways for the synthesis of various higher alcohols. Moreover, in this chapter, metabolic engineering studies for the production of higher alcohols are reviewed. Recent advances and challenges associated with the microbial synthesis of higher alcohols are discussed.
The second-generation biobutanol production from lignocellulosic material is one of the key interests for research, considering the future of alternative energies based on the circular economy action plans. An important part of the butanol production process depends on the substrate, and therefore on the pretreatment technologies available for decreasing costs and to obtain the highest release of sugars, for a better performance of the microorganism during fermentation. This chapter is a current overview of the diverse pretreatment processes based on their classification, importance, drawbacks, and applications with the objective of facilitating to identify the elements to be considered specifically for butanol production using Clostridium strains.