Consolidated bioprocessing for bioethanol production by metabolically engineered Bacillus subtilis strains

Expression and characterization of a novel β-1,4-endoglucanase from Bacillus subtilis strain isolated from a pulp and paper mill wastewater

The production of fermentable sugars from lignocellulosic biomass is achieved by the synergistic action of a group of enzymes called cellulases. Cellulose is a long chain of chemically linked glucoses by β-1,4 bonds. The enzyme β-1,4-endoglucanase is the first cellulase involved in the degradation, breaking the bond of the amorphous regions. A β-1,4-endoglucanase enzyme with high activity was obtained from a Bacillus subtilis strain isolated from wastewater of a pulp and paper mill. Sequencing and bioinformatic analysis showed that the gene amplified by PCR consisting of 1407 nucleotides and coding for a β-1,4-endoglucanase enzyme of approximately 55 kDa. The open reading frame (ORF) encoding the mature endoglucanase (eglS) was successfully inserted in a modified cloning plasmid (pITD03) and into the pYD1 plasmid used for its expression in yeast. Carboxymethylcellulose (CMC) plate assay, SDS-PAGE, and zymogram confirmed the production and secretion by the transformed E. coli BL21-SI strain of a 39 kDa β-1,4-endoglucanase consistent with the catalytic domain without the cellulose-binding module (CBM). The results showed that the truncated β-1,4-endoglucanase had higher activity and stability.

Investigation of the influence of Candida tropicalis on bioethanol production using sugarcane bagasse: stochastic and in silico analysis

This study investigated the impact of Candida tropicalis NITCSK13 on sugarcane bagasse (SCB) consolidated bioprocessing (CSB) using various parameters, such as pH, steam explosion (STEX) pretreatment, and temperature (at two different temperatures, cellulose hydrolysis and ethanol fermentation). The backpropagation neural network (BPNN) method simulated the optimal CSB conditions, achieving a maximum ethanol yield of 44 ± 0.32 g/L (0.443 g of ethanol/g of SCB) from STEX pretreated SCB within 48 h at 55 °C for cellulose hydrolysis and 33 °C for ethanol fermentation and pH 3.5. The simulated conditions were experimentally validated and showed an R2 value of 0.998 and absolute average deviation (AAD) of 1.23%. The strain NITCSK13 also exhibited a high ethanol tolerance of 16% (v/v). The interactions between the inhibitors, cellobiose, furfural, and thermocellulase were assessed through molecular docking. The results revealed a maximum inhibitory constant of 3.7 mM for furfural against the endoglucanase (EnG) of Humicola insolens (2ENG) at 50 °C. Acremonium chrysogenum endoglucanase (5M2D) exhibited a maximum of 88.7 µM for cellobiose at 50 °C. The SWISS homology model of EnG from Candida viswanathii exhibited inhibitory effects similar to those of EnG from Thermoascus and Thermotoga, indicating that the moderately thermophilic yeast Candida sp. cellulase may be capable of efficiently tolerating inhibitors and could be a promising candidate for consolidated bioprocessing of cellulosic ethanol.

Innovative approaches for amino acid production via consolidated bioprocessing of agricultural biomass

Agricultural plantations in Indonesia and Malaysia yield substantial waste, necessitating proper disposal to address environmental concerns. Yet, these wastes, rich in starch and lignocellulosic content, offer an opportunity for value-added product development, particularly amino acid production. Traditional methods often rely on costly commercial enzymes to convert biomass into fermentable sugars for amino acid production. An alternative, consolidated bioprocessing, enables the direct conversion of agricultural biomass into amino acids using selected microorganisms. This review provides a comprehensive assessment of the potential of agricultural biomass in Indonesia and Malaysia for amino acid production through consolidated bioprocessing. It explores suitable microorganisms and presents a case study on using Bacillus subtilis ATCC 6051 to produce 9.56 mg/mL of amino acids directly from pineapple plant stems. These findings contribute to the advancement of sustainable amino acid production methods using agricultural biomass especially in Indonesia and Malaysia through consolidated bioprocessing, reducing waste and enhancing environmental sustainability.

Current status of metabolic engineering of microorganisms for bioethanol production by effective utilization of pentose sugars of lignocellulosic biomass

Lignocellulosic biomass, consisting of homo- and heteropolymeric sugars, acts as a substrate for the generation of valuable biochemicals and biomaterials. The readily available hexoses are easily utilized by microbes due to the presence of transporters and native metabolic pathways. But, utilization of pentose sugar viz., xylose and arabinose are still challenging due to several reasons including (i) the absence of the particular native pathways and transporters, (ii) the presence of inhibitors, and (iii) lower uptake of pentose sugars. These challenges can be overcome by manipulating metabolic pathways/glycosidic enzymes cascade by using genetic engineering tools involving inverse-metabolic engineering, ex-vivo isomerization, Adaptive Laboratory Evolution, Directed Metabolic Engineering, etc. Metabolic engineering of bacteria and fungi for the utilization of pentose sugars for bioethanol production is the focus area of research in the current decade. This review outlines current approaches to biofuel development and strategies involved in the metabolic engineering of different microbes that can uptake pentose for bioethanol production.

Engineering the Metabolic Landscape of Microorganisms for Lignocellulosic Conversion

Bacteria and yeast are being intensively used to produce biofuels and high-added-value products by using plant biomass derivatives as substrates. The number of microorganisms available for industrial processes is increasing thanks to biotechnological improvements to enhance their productivity and yield through microbial metabolic engineering and laboratory evolution. This is allowing the traditional industrial processes for biofuel production, which included multiple steps, to be improved through the consolidation of single-step processes, reducing the time of the global process, and increasing the yield and operational conditions in terms of the desired products. Engineered microorganisms are now capable of using feedstocks that they were unable to process before their modification, opening broader possibilities for establishing new markets in places where biomass is available. This review discusses metabolic engineering approaches that have been used to improve the microbial processing of biomass to convert the plant feedstock into fuels. Metabolically engineered microorganisms (MEMs) such as bacteria, yeasts, and microalgae are described, highlighting their performance and the biotechnological tools that were used to modify them. Finally, some examples of patents related to the MEMs are mentioned in order to contextualize their current industrial use.

The silkworm (Bombyx mori) gut microbiota is involved in metabolic detoxification by glucosylation of plant toxins

Herbivores have evolved the ability to detoxify feed components through different mechanisms. The oligophagous silkworm feeds on Cudrania tricuspidata leaves (CTLs) instead of mulberry leaves for the purpose of producing special, high-quality silk. However, CTL-fed silkworms are found to have smaller bodies, slower growth and lower silk production than those fed mulberry leaves. Here, we show that the high content of prenylated isoflavones (PIFs) that occurred in CTLs is converted into glycosylated derivatives (GPIFs) in silkworm faeces through the silkworm gut microbiota, and this biotransformation is the key process in PIFs detoxification because GPIFs are found to be much less toxic, as revealed both in vitro and in vivo. Additionally, adding Bacillus subtilis as a probiotic to remodel the gut microbiota could beneficially promote silkworm growth and development. Consequently, this study provides meaningful guidance for silk production by improving the adaptability of CTL-fed silkworms.

Bioeconomy and net-zero carbon: lessons from Trends in Biotechnology, volume 1, issue 1

Many biotechnology applications tend to be for low production volumes and relatively high-value products such as insulin and vaccines. More difficult to perfect at scale are bioprocesses for high-volume products with lower value, especially if the target product is a reduced chemical such as a solvent or a plastic. Historically, industrial microbiology succeeded under special circumstances when fossil feedstocks were either unavailable or expensive. Inevitably, as these circumstances relaxed, bioprocesses struggled to compete with petrochemistry. Why try to compete? Fossil resources will be phased out in the coming decades in the struggle with climate change. To reach net-zero carbon by 2050 will require all sectors to transition, not only energy and transportation. This may herald a new opportunity for industrial bioprocesses with much better tools.

Reclamation of ginseng residues using two-stage fermentation and evaluation of their beneficial effects as dietary feed supplements for piglets

Environmental pollution caused by herbal residues, such as ginseng residue (GR), and the huge waste of medicinal ingredients in such residues hinder the development of the pharmaceutical industry. Few studies focused on the biotransformation of GRs and the practical utilization of their bioproducts. In this study, we developed a two-stage fermentation method to optimize GR bioconversion and used the fermented products as dietary supplements for piglets. The tested GR contained abundant lignocelluloses, protein, sugar, and amino acids. Approximately 43.10% of the total lignocelluloses were degraded into sugars by Inonotus obliquus in stage 1 of fermentation. Meanwhile, the sugar content increased by 36.20%, which became the feed for Bacillus subtilis and Saccharomyces cerevisiae in stage 2 of fermentation. These two strains boosted the production of bacterial proteins and other metabolites, including peptides, organic acids, and amino acids. At the end of fermentation, the contents of bioactive compounds significantly increased by 3.18%-21.79%. The dietary supplementation of fermented GR significantly improved the growth performance (6.47%-7.98%), intestinal microbiota, immune function, and healthy status and reduced the diarrhea incidence and noxious gas emission of the piglets. This study provides evidence-based results for the development and deployment of a circular economy between ginseng and livestock industries.

Factors affecting the competitiveness of bacterial fermentation

Sustainable production of chemicals and materials from renewable non-food biomass using biorefineries has become increasingly important in an effort toward the vision of 'net zero carbon' that has recently been pledged by countries around the world. Systems metabolic engineering has allowed the efficient development of microbial strains overproducing an increasing number of chemicals and materials, some of which have been translated to industrial-scale production. Fermentation is one of the key processes determining the overall economics of bioprocesses, but has recently been attracting less research attention. In this Review, we revisit and discuss factors affecting the competitiveness of bacterial fermentation in connection to strain development by systems metabolic engineering. Future perspectives for developing efficient fermentation processes are also discussed.

Potato peel waste biorefinery for the sustainable production of biofuels, bioplastics, and biosorbents

Potato is the fourth most abundant crop harvested annually worldwide. Potato peel waste (PPW) is the main waste stream of potato-processing industries which is generated in large quantities and is a threat to the environment globally. However, owing to its compositional characteristics, availability, and zero cost, PPW is a renewable resource for the production of high-value bioproducts. Hence, this study provides a state-of-the-art overview of advancements in PPW valorization through biological and thermochemical conversions. PPW has a high potential for biofuel and biochemical generation through detoxification, pretreatment, hydrolysis, and fermentation. Moreover, many other valuable chemicals, including bio-oil, biochar, and biosorbents, can be produced via thermochemical conversions. However, several challenges are associated with the biological and thermochemical processing of PPW. The insights provided in this review pave the way toward a PPW-based biorefinery development, providing sustainable alternatives to fossil-based products and mitigating environmental concerns.

Analysis of Bacterial Diversity in Different Types of Daqu and Fermented Grains From Danquan Distillery

Bacterial communities in high-temperature Daqu and fermented grains are important for brewing Jiang-flavor Baijiu such as Danquan Baijiu. Daqu is a saccharifying and fermenting agent, which has a significant impact on the flavor of Baijiu. However, bacterial communities in three different types of samples from the Danquan distillery (dqjq_ck, dqjqcp, and dqjp3) were still unclear, which limited further development of Danquan Baijiu. “dqjq_ck” and “dqjqcp” indicate high-temperature Daqu at days 45 and 135, respectively. “dqjp3” indicates fermented grains. In this study, the bacterial communities of three samples were analyzed by Illumina Miseq high-throughput sequencing. The bacterial communities of three samples primarily composed of thermophilic bacteria and bacteria with stress resistance. The most abundant species in dqjq_ck, dqjqcp, and dqjp3 were Comamonas, Bacillus, and unclassified Lactobacillales, respectively. The main bacteria included Bacillus, Comamonas, Myroides, Paenibacillus, Acetobacter, Kroppenstedtia, Staphylococcus, Saccharopolyspora, Planifilum, Lactobacillus, Acinetobacter, Oceanobacillus, Enterococcus, Thermoactinomyces, Lactococcus, Streptomyces, Saccharomonospora, Tepidimicrobium, Anaerosalibacter, unclassified_Lactobacillales, unclassified_Thermoactinomycetaceae_1, unclassified_Bacillaceae_2, unclassified_Bacillales, unclassified_Microbacteriaceae, unclassified_Rhodobacteraceae, unclassified_Actinopolysporineae, and unclassified_Flavobacteriaceae in three samples (percentage was more than 1% in one of three samples). In our study, the succession of microbiota in three samples representing three important stages of Danquan Baijiu brewing was revealed. This article lays a good foundation for understanding the fermentation mechanism and screening some excellent indigenous bacteria to improve the quality of Danquan Baijiu in future.

Consolidated bioprocessing of lignocellulosic biomass: Technological advances and challenges

Consolidated bioprocessing (CBP) is characterized by a single-step production of value-added compounds directly from biomass in a single vessel. This strategy has the capacity to revolutionize the whole biorefinery concept as it can significantly reduce the infrastructure input and use of chemicals for various processing steps which can make it economically and environmentally benign. Although the proof of concept has been firmly established in the past, commercialization has been limited due to the low conversion efficiency of the technology. Either a native single microbe, genetically modified microbe or a consortium can be employed. The major challenge in developing a cost-effective and feasible CBP process is the recognition of bifunctional catalysts combining the capability to use the substrates and transform them into value-added products with high efficiency. This article presents an in-depth analysis of the current developments in CBP around the globe and the possibilities of advancements in the future.

Metagenomic psychrohalophilic xylanase from camel rumen investigated for bioethanol production from wheat bran using Bacillus subtilis AP

Bioethanol produced from lignocellulosic biomass is regarded as a clean and sustainable energy source. The recalcitrant structure of lignocellulose is a major drawback to affordable bioethanol production from plant biomass. In this study, a novel endo-1,4-xylanase, named Xyn-2, from the camel rumen metagenome, was characterized and evaluated for hydrolysis of agricultural wastes. The enzyme was identified as a psychrohalophilic xylanase with maximum activity at 20 °C, keeping 58% of the activity at 0 °C, and exhibiting twice as much activity in 0.5–4 M NaCl concentrations. Xyn-2 was able to hydrolyze wheat bran (100%), sunflower-seed shell (70%), wheat straw (56%), rice straw (56%), and rice bran (41%), in the relative order of efficiency. Besides, the ethanologenic B. subtilis AP was evaluated without and with Xyn-2 for bioethanol production from wheat bran. The strain was able to produce 5.5 g/L ethanol with a yield of 22.6% in consolidated bioprocessing (CBP). The contribution of Xyn-2 to ethanol production of B. subtilis AP was studied in an SSF system (simultaneous saccharification and fermentation) giving rise to a significant increase in ethanol production (p ≤ 0.001) to a final concentration of 7.3 g/L with a yield of 26.8%. The results revealed that the camel rumen metagenome might be an invaluable source of novel xylanolytic enzymes with potential application in lignocellulosic biomass valorization. At the same time, the results suggest that B. subtilis with a diverse carbon-source preference and sophisticated systems for production and secretion of enzymes might be a promising candidate for strain development for bioethanol production from plant biomass. It might be assumed that the fortification of B. subtilis enzymatic arsenal with select xylanolytic enzymes from camel rumen metagenome may have a great impact on bioethanol production.

Structural and Biochemical Analysis of the Furan Aldehyde Reductase YugJ from Bacillus subtilis

NAD(H)/NADP(H)-dependent aldehyde/alcohol oxidoreductase (AAOR) participates in a wide range of physiologically important cellular processes by reducing aldehydes or oxidizing alcohols. Among AAOR substrates, furan aldehyde is highly toxic to microorganisms. To counteract the toxic effect of furan aldehyde, some bacteria have evolved AAOR that converts furan aldehyde into a less toxic alcohol. Based on biochemical and structural analyses, we identified Bacillus subtilis YugJ as an atypical AAOR that reduces furan aldehyde. YugJ displayed high substrate specificity toward 5-hydroxymethylfurfural (HMF), a furan aldehyde, in an NADPH- and Ni²⁺-dependent manner. YugJ folds into a two-domain structure consisting of a Rossmann-like domain and an α-helical domain. YugJ interacts with NADP and Ni²⁺ using the interdomain cleft of YugJ. A comparative analysis of three YugJ structures indicated that NADP(H) binding plays a key role in modulating the interdomain dynamics of YugJ. Noticeably, a nitrate ion was found in proximity to the nicotinamide ring of NADP in the YugJ structure, and the HMF-reducing activity of YugJ was inhibited by nitrate, providing insights into the substrate-binding mode of YugJ. These findings contribute to the characterization of the YugJ-mediated furan aldehyde reduction mechanism and to the rational design of improved furan aldehyde reductases for the biofuel industry.