Bioreactors are central equipment used in the majority of bioprocesses. Different models of bioreactors have been developed for different processes, which can be applied either for submerged or for solid-state fermentation. Scale-up involves the development of bioprocess in bench, pilot, and industrial scales. Optimal conditions are first screened and determined in the bench scale and so that the process can be transferred to a larger scale. This transferring requires the proper reproduction of conditions and performance, being a major challenge since important aspects, such as aeration and agitation, are critical for cells development. In this case, scale-up strategies are employed to maintain bioprocesses’ performance. These strategies are based on geometric similarity aspects of bioreactors, agitation, and aeration conditions, which must follow the requirements of each bioprocess and the used microorganisms. Operational conditions significantly impact cell growth and, consequently, the biosynthesis of different biomolecules, which must then be reproduced at higher scales. For this purpose, one or more operating factors can be maintained constant during scale-up with the possibility to predict, for example, the power consumption of large-scale bioreactors or aeration conditions in an aerobic culture. This review presents the most employed bioreactors’ scale-up strategies. In addition, the scale-up of other bioreactors models, such as pneumatic and solid-state fermentation bioreactor and even photobioreactors, will also be described with some examples.
The human gastrointestinal tract harbors a complex microbiota, pivotal in maintaining health equilibrium. Disruption of this microbial balance has implications for myriad health conditions. Probiotics, beneficial microbial entities, have demonstrated potential in rectifying gut microbiota imbalances, offering health benefits and disease prevention. This review elucidates the nuanced roles of probiotics, emphasizing their interactions with both pathogenic and commensal gut microorganisms. Recent breakthroughs in the identification of potent probiotic strains and their prospective applications in biomedical research are delineated. Comprehensive analyses of clinical studies underscore the safety, efficacy, and applicability of probiotics in diverse food and therapeutic avenues. As probiotic research burgeons, this review amalgamates current insights with future directions, accentuating the transformative prospects of probiotics in contemporary biomedical paradigms. The gut's microflora plays a cardinal role in nutrient metabolism, immune modulation, and protection against pathogens. Disturbances in this microflora can lead to dysbiosis, with potential repercussions for digestive and systemic health. Probiotics exert their beneficial effects through multiple mechanisms, including competitive exclusion of pathogens, production of antimicrobial substances, and modulation of the host's immune response. Their health benefits encompass not only gastrointestinal health, such as in the management of diarrhea, irritable bowel syndrome, and inflammatory bowel diseases but also systemic effects in areas like immune modulation and mental health. The growing recognition of these benefits has led to a surge in the market demand for probiotic supplements and fortified foods, with research continually unveiling novel strains and applications.
The past decade has been envisaged as a period of unprecedented growth and development in the bioprocessing industry due to the increasing prominence of manufacturing bioproducts encompassing day-to-day life. Bioprocesses are the heart of biotechnology and represent the most dynamic constituent for conceptualizing the bioeconomy as it has the potential to tackle the most burgeoning problems such as climatic adversity, global population growth, reduced ecosystem resilience. The promising amalgamation of digitalization, biologicalization, and biomanufacturing paved the way for an emerging concept of “bio-intelligent value addition” or more prominently Bioprocessing 4.0 that enables the transformation in the landscape of biomanufacturing. Despite its positive credentials, the technology is facing technical, organizational, economical, and likely some unforeseen challenges that must be resolved for its successful implementation for hailing the sustainability development goals (SDGs) of bioeconomy. Though the road of bioeconomy is quite arduous, the continuous demand for bioproducts and their timely delivery at a faster rate necessitates the culture of sharing knowledge, digitalization, automation, and development of flexible modular and podular facility footprints to accelerate biomanufacturing. Therefore, it is worth summarizing the major portfolios of Bioprocessing 4.0 such as conception of biofoundry, bioprocess intensification strategies, process and data analytics, software and automation, and its synergistic correlation with bioeconomy. Thus, the present article advocates about the technological glance of Bioprocessing 4.0 along with technical challenges and future research priorities for sparking the glory of this industrial landscape for enshrining the bioeconomy.
The biorefinery approach ensures a sustainable source of valuable fatty acids and opens up new avenues for their application in healthcare industries. Recent studies highlight the health benefits of omega-PUFAs, spurring the search for cost-effective production methods. Microbial platforms are promising for high-yield PUFA production, with ω-3 dominating the market. ω-3 PUFAs offer antioxidant and anti-inflammatory effects, reducing illness risk, while all PUFAs contribute to cardiovascular health, diabetes prevention, cancer risk reduction, and more. ω-6 PUFAs, particularly linoleic acid (LA) and arachidonic acid (ARA), play vital roles in various aspects of health, making them high-demand bioavailable compounds. Additionally, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) exhibit potential benefits in brain development and COVID-19 prevention. This comprehensive review provides insights into the state-of-the-art microbial biorefinery strategies for ω-3 and ω-6 PUFA production and their wide-ranging health-related benefits.
Docosahexaenoic acid (DHA, C22H32O2, C22:6 ω-3) and Eicosapentaenoic acid (EPA, C20H30O2 C20:5 ω-3), are biomolecules from the group of omega 3 polyunsaturated fatty acids (PUFA). In recent decades, a large number of clinical and epidemiological studies have demonstrated the benefits of this molecule for improving human health and preventing various diseases. Based on this, the demand for this bioproduct has grown year after year, to the point where traditional long-term production cannot keep up with the consumer market itself. With this problem in mind, this review article aims to provide an overview of the current state of sustainable production of omega-3 PUFAs. A comparative survey of microorganisms from the thraustochytrid family with other species of microorganisms from other kingdoms and families was carried out to show the best potential for microbial oil production. The comparison involved an in-depth analysis of the scientific literature and patents currently registered on the subject. The results showed that thraustochytrids have more advantages and practicality in a wider variety of substrates and culture media than their other competitors. Therefore, with the ever-increasing demand for human and animal needs, the study and application of species that produce and accumulate fatty acids is becoming increasingly urgent. Thus, obtaining omega-3 through microbial oil represents a sustainable and economically viable alternative for the future.
Pseudomonas sp. has been considered one of the most promising microbial platform strains due to its versatile metabolism, enabling the valorization of waste materials into value-added chemical products. As the native producer of polyhydroxyalkanoates (PHAs), the biodegradable biopolyesters, it has been widely engineered by various metabolic engineering tools for the production of PHAs composed of short-chain-length and medium-chain-length monomers with adjustable composition from diverse carbon sources, ranging from pure sugars to crude oils and fatty acids. This review discusses the feasibility of Pseudomonas sp. as the industrial host strain and the recent advances regarding the systems metabolic engineering strategies for PHAs production in Pseudomonas sp.
At present, industrial beer is becoming increasingly saturated, craft beer has become the favorite of more and more consumers. Specialty malt have a more dramatic impact on the flavor and color of the beer. The quality of specialty malt was significantly related to the Maillard reaction products (MRPs), which play a pivotal role in the beer production and storage. The shelf life of beer depends on the antioxidant properties of the MRPs, which have a significant impact on the color, flavor and biological activity of specialty malt. Although the reactions between proteins and carbohydrates have been extensively studied, the effects of MRPs on the color, flavor, and biological activity of specialty malt have not been fully elucidated. The types and content of MRPs in the specialty malt, which can be used to estimate the contribution of MRPs from malts to beer, were summarized in this review. Then, its potential biological activity in antibacterial, antioxidant properties and intestinal microbial regulation were evaluated, with some negative effects of MRPs of specialty malt were further discussed. In addition, the research needs are also prospected and it provides a future direction for the production of high-quality specialty malt with hazardous by-products reduced and directed beneficial products accumulating.
Indole is a signalling molecule produced both by bacteria and plants. In this review its signalling role between microbes and in particular in the human gut is discussed. Besides the natural roles, indole also has value for flavour and fragrance applications, for example, in food industry or perfumery. Additionally, indole can be derivatized to several halogenated and oxygenated compounds that can be used as natural colourants or have promising bioactivity with therapeutic potential to treat human diseases. Indole is traditionally obtained from coal tar. Biocatalytic approaches have been developed to convert indole into halogenated and oxygenated derivatives. This review will discuss recent advances in production of indole from glucose or tryptophan by fermentation and the production of derived halogenated and oxygenated derivatives by microbial cell factories.
Omega-3 fatty acids are polyunsaturated fatty acids that are vital for human food consumption and metabolism. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two long-chain polyunsaturated fatty acids (LC-PUFAs), are primarily obtained from diatoms in the oceanic food web. Though microalgae are the main producers of EPA and DHA, but currently, only few algal strains are known to produce large levels of EPA and DHA. The demand for nutraceuticals has significantly increased because of people’s increased awareness and health consciousness. Due to foods being the concentrated supply of omega-3 PUFAs (polyunsaturated fatty acids), this has increased the demands on aquatic sources of n-3 PUFAs. Micro-algal sources must be carefully examined due to the numerous drawbacks and difficulties of fish oils and the lack of DHA and EPA in plant sources. This review focuses on the current state of omega-3 PUFA (polyunsaturated fatty acids) production, sources, and market demand to provide an overview of sources that are being explored for sustainability as well as current and anticipated market trends in the omega-3 industry. This will make it possible for them to be produced on a wide scale for the benefit of human health.
Biogas reactors operating with protein-based biomass have a high methane potential and industrial value. Protein-rich materials, including gelatin processing and ossein factory waste, are suitable feedstocks for use in ammonia-tolerant biogas digesters. However, the anaerobic digestion of these materials is limited by the accumulation of ammonia, hydrogen sulfide, and lactic acid. A stable biogas starter is required for efficient biogas production from protein-based mass and process performance. Hence, various ammonia-tolerant biogas inocula, immobilization carriers used, culture formulations, and stater stability are comprehensively summarized in this review. We also discuss engineered methanogens and mutants to improve methane productivity. The genera Methanoculleus and Methanosarcina are the dominant ammonia-tolerant methanogens studied in different biogas plants; however, their ammonia-tolerant molecular mechanisms remain unclear. Recent advances in omics technologies, systems, and synthetic biology of methanogens have been reviewed and discussed for the design and development of methanogenic inocula. We described the genome-centric characteristics of methanogenic consortia to improve the process efficiency under the desired environmental conditions. We also focus on the perspective of methanogenic culture development for the co-production of acetone–butanol–ethanol and methane as well as odor control strategies. A novel metabolic scaffold “Protein Catabolism-Directed Methanogenesis” was discovered from a methanogenic culture using a systems biology approach. This review offers new insights into the feasibility of ammonia-tolerant biogas starters and engineering synthetic pathways for recycling gelatin processing waste into biofuels in the energy sector.
The sudden outbreak of the COVID-19 pandemic made people around the world more concerned about health and food safety. As a part of healthy diets, consumption of fruits and vegetables is essential to build strong immunity against various chronic diseases. However, contamination of fruits and vegetables may occur from farm to fork in the food supply chain process, thus affecting their post-harvest quality. Various disinfection technologies have been developed to prevent foodborne outbreaks caused by the consumption of unsafe food. This comprehensive review delves into the fundamental principles of physical, chemical, and novel treatments and their impact on the quality and shelf life of a wide range of fruits and vegetables. Chemical treatments such as chlorine dioxide, ozone, electrolyzed water, high-pressure carbon dioxide, and organic acids, as well as physical treatments, such as hot water blanching, steam blanching, and microwave blanching, have been discussed. Moreover, novel treatments such as cold plasma, UV light, pulsed electric field, and high hydrostatic pressure have also been explored. These treatments can be tailored to specific fruits and vegetables and integrated into food safety protocols to reduce the risk of foodborne outbreaks and improve the shelf life of these products.
Waste management is undergoing a rapid transformation into the waste valorization industry, with biological and chemical refining methods currently emerging as the most appealing options. To maintain competitiveness, staying well informed about the latest advancements and promptly adapting to evolving trends is essential. However, not all stakeholders have the necessary time to closely monitor and assess the intricacies associated with ever-changing regulations, customer preferences, societal concerns, post-pandemic conditions, climate change, and the various other challenges within the global market. The overarching objective of this paper is to pinpoint the most economically promising technologies, thereby encouraging a shift away from linear economic models and fostering the adoption of concepts like sustainability, social responsibility, and circularity in waste management. It is deduced that the highest potential lies in the gradual refinement of valuable components. Currently, the most promising avenues for management appear to be as follows, ranked in descending order of managerial viability: (A) The production of cleansing products and feed through insect rearing; (B) the creation of fertilizers through the regeneration of phosphorus and nitrogen; and (C) the development of cement substitutes through pyrolysis.
The growing global demand for food has exposed the unsustainable nature of our current food system, necessitating a transition towards a more sustainable model. This sustainable system should emulate natural processes, operating in a circular manner where the output of one phase serves as the input for the next. This concept is known as the circular food economy. Innovative technologies have emerged, harnessing food by-products to create textiles, cosmetics, organic fertilizers, and biodegradable packaging. However, several obstacles, including unreliable food waste estimates, limited financial resources, inadequate technological infrastructure, and legal frameworks, hinder progress towards a circular food economy. To facilitate this shift, substantial investments are required in advanced infrastructure and technologies, promoting resource efficiency. This paper delves into the potential of a circular food economy as a viable alternative to the current linear supply chain, emphasizing the importance of closing the loop for a more sustainable and efficient food system.
3-ketosteroid Δ1-dehydrogenases (Δ1-KstDs) are FAD-dependent and substrate-inducing enzymes, which catalyze the introduction of double bonds between C1 and C2 atoms of the A ring of 3-ketosteroid substrates. They are essential in the initial stages of the steroid core's breakdown. Additionally, Δ1-KstDs are particularly intriguing for applications in pharmaceutical manufacturing, environmental bioremediation, and the etiology of infectious illnesses. A wide range of microorganisms, particularly bacteria from the phylum Actinobacteria, have Δ1-KstDs. Δ1-KstDs can be classified into at least seven separate groups based on the sequence data in NCBI, and the enzymes in each group exhibit unique structural and catalytic properties. Understanding these properties completely is crucial for utilizing and developing Δ1-KstDs in metabolic engineering and enzyme engineering. This review describes and explains the biochemical and enzymatic characteristics of Δ1-KstDs based on a phylogenetic tree. To assist in the selection of highly active enzymes for engineering applications, the three-dimensional structures of Δ1-KstDs associated with enzyme mechanisms are stressed. The biotechnological application of microbial Δ1-KstDs is also covered in this article, including genetic engineering based on metabolic strains and related genetic modification techniques for creating new productive industrial strains, the development and transformation of the heterologous expression system, the molecular modification and the optimization of catalytic conditions, and the use of microbial fermentation to increase product yield. Furthermore, we also highlight the recent development in the use of isolated Δ1-KstDs combined with a FAD cofactor regeneration system. We conclude by summarizing the concepts and techniques used in subsequent research and application development. All of these knowledge might serve as a guide for new mining and industrial applications in Δ1-KstDs.
Methanotrophs, relying on methane as their primary carbon source, are renowned for their exceptional capacity to generate a diverse range of methane-based bioproducts, making the unraveling of associated metabolic pathways a vital endeavor. This study focuses on Methylosinus trichosporium OB3b to investigate genes associated with biomanufacturing of commercially relevant metabolites through an integrated approach combining genome sequencing and metabolomic analysis. The complete genome of OB3b was sequenced using Nanopore technology, revealing a total of 4877 genes within the chromosome. Genetic organization of the pili operon in OB3b revealed the presence of a Type IVb pili system, shedding light on adhesion genes, maturation genes, quorum sensing genes, and regulatory genes. Analysis of the biosynthetic gene cluster in OB3b revealed 11 distinct regions, including a notable non-ribosomal protein synthetase associated with rhizomide production. In addition, the study focused on 14 commercially significant metabolites among 63 analyzed by metabolomics and identified bifunctional aldehyde dehydrogenase and phospholipase in the ethanolamine pathway, while identifying fatty acid desaturase in the R-decenoic acid pathway. Additionally, the study predicted a methane-derived pathway for trehalose synthesis. This research unlocks the untapped potential of methanotrophs in biotechnology and provides valuable insight into pathways for the production of desired metabolite.
Pomegranate, renowned for its delectable taste and remarkable nutritional profile, has witnessed a surge in both production and consumption. However, the by-products generated during industrial processes, such as peels and seeds, have the potential for adverse environmental impacts if not meticulously managed. Similarly, expired fruit juices or spillages that may occur during manufacturing and transportation contribute to agri-food waste. This study focused on the comprehensive assessment of pomegranate by-products and pomegranate juice using ascomycetes and zygomycetes filamentous fungi, namely Aspergillus oryzae, Rhizopus oligosporus, and Neurospora intermedia to obtain mycoprotein for sustainable vegan food production. The findings revealed that pomegranate juice, both fresh and expired commercial, contained essential nutrients for fungal biomass production (up to 0.024 g biomass/mL juice). Nonetheless, fresh juice emerges as a more potent medium in terms of protein production than commercial juice. Cultivating A. oryzae yielded a biomass of 0.39 (g biomass/g peel) from pomegranate peel, while concurrently raising the protein content of raw pomegranate peel from 30.89 g/kg to 85.41 g/kg. Furthermore, incorporating yeast extract into the peel medium not only resulted in an enhanced biomass yield of 0.49 (g biomass/g peel) but also significantly elevated the protein content to 198.63 g/kg. This study provides valuable insights into the potential of pomegranate peel and juice as promising substrate for fungal biomass production, offering opportunities for the development of innovative food and feed products.
Microencapsulation is an efficient way to increase the survival rate of probiotics against harsh conditions. In this study, three probiotic strains (Lactiplantibacillus plantarum subsp. plantarum strain W2 (LP4), Lactiplantibacillus pentosus strain XL640 (LPE1), and Limosilactobacillus fermentum strain W8 (LF2)), isolated from shalgam and gilaburu, were microencapsulated with spray drying and process conditions [maltodextrin concentration (MC, 10–30%) and inlet air temperature (IAT, 110–130 °C)] were optimized by central composite rotatable design of response surface methodology. The results indicated that the predicted IAT and MC values for the maximum powder yield and viability were 123.21 °C and 22.76%, 130.37 °C and 19.49%, and 127.94 °C and 10.00% for LF2, LP4 and LPE1, respectively. At these conditions, bacterial viability ranged from 10.27 to 10.33 log colony-forming units per gram (cfu/g), while the powder yield values for the encapsulation of the bacteria were between 43.38% and 50.97%. Furthermore, MC was the most significant factor for the powder yield of LF2, LPE1, and viability of LPE1. Encapsulation efficiency values higher than 92.77% demonstrated the efficiency of spray drying for the protection of selected strains. The microcapsules produced at the optimum points had moisture content between 5.30 and 5.96%. SEM images showed that the microcapsules were in spherical shape. In conclusion, the results confirmed that the selected probiotics were successfully microencapsulated with spray drying with high powder yield, viability, and encapsulation efficiency levels and these features could reveal the potential of the encapsulated probiotic strains to be used in high-sugar foods.
The study investigated the enhanced production of 2-hydroxybutyric acid (2-HBA) from threonine using a two-step whole-cell bioconversion by recombinant Escherichia coli BL21 (DE3) overexpressing threonine dehydratase and keto-reductase. To address the rate-limiting step posed by NADH regeneration for the keto-reductase reaction converting 2-ketobutyric acid (2-KBA) to 2-HBA, formate dehydrogenase from Candida boidinii was overexpressed under the T7 promoter, resulting in a high titer of 1015 mM and a yield of 0.70 mol/mol. Furthermore, the yield was improved by disrupting three enzymes responsible for the degradation of the intermediate (2-KBA), pyruvate-formate lyase (PflB), pyruvate oxidase (PoxB), and pyruvate dehydrogenase complex (PDHc), leading to an impressive yield of 0.99 mol/mol, closely approaching the theoretical maximum of 1.00 mol/mol. The triple mutant, designed to prevent 2-KBA degradation, achieved a remarkable titer of 1,400 mM and volumetric productivity of 58 mmol/L/h. To the best of our knowledge, this achievement represents the highest reported titer and yield for 2-HBA production to date.
Lignin is an essential raw material that shows huge potential in novel value-added industrial applications. Most of previous researches on production of lignin from biological sources are confined to laboratory endeavors owing to the paucity of basic process engineering studies on lignin extraction from bio-material. Therefore, this investigation is aimed at optimizing lab based proof-of-concept, computer-aided batch simulation and techno-economic assessment of scale-up process design of lignin recovery from sawdust. Box–Behnken design was used to design and optimize lignin recovery from sawdust at varied temperature (60–100 °C), time (90–270 min) and concentration of NaOH (15–25%). Aspen Batch Process Developer was used for the simulation of the recovery and scale-up design of the recovery of lignin, techno-economic analysis models were developed for the evaluation of commercialization potential of the scale-up study while sensitivity and uncertainty analysis was carried out using Monte Carlo simulation to study the effect of key parameters on the techno-economic analysis developed models. The simulated results from Aspen Batch Process Developer and optimum experimental condition for the recovery of lignin are in agreement with a deviation of 0.0025, cycle time of 1445 min and flowrate of 0.00084 g/min at base case condition. The techno-economic analysis show that recovery of 50,000 kg/batch of lignin was possible and the optimum condition that are Fixed Capital Investment ($21.5 M), interest rate (10.25%) and Cost of Lignin ($1) lead to a profitability response of net present value ($34.97), internal rate of return (34.14%) and productivity index ($1.62) for a 15-year investment plan. The sensitivity and uncertainty analysis is favorable to the simulation study used for this prediction.
In recent times, the microalga Chlorella vulgaris has attracted significant attention due to its multifaceted applications in diverse disciplines. Nonetheless, discrepancies in growth rates and biomass yield are observed across freshwater and saline environments. This research was designed to elucidate the impacts of varying concentrations of NaHCO3, NPK fertilizer, and NaCl on the proliferation of Chlorella vulgaris cultivated in 288L plastic bottle bioreactors, ensuring optimal light exposure and aeration for algal propagation. Biomass quantifications were executed tri-weekly, utilizing metrics such as optical density (OD) and biomass concentration (mg/L). Post a 30-day cultivation period, the findings revealed that optimal biomass was attained with an augmentation of 30 mg/L NaHCO3 and 100 mg/L NPK. Remarkably, the alga manifested resilience to escalating salinity levels, recording a peak biomass of 1036 mg/L upon the introduction of 20 g/L NaCl. Moreover, the research underscored a robust correlation between optical density (OD) and biomass concentration (mg/L) amidst diverse salinity regimes, underscoring the criticality of these parameters in the proliferation of Chlorella vulgaris.
Boldenone is a protein-assimilating androgen steroid that can promote protein synthesis, support nitrogen storage, and enhance renal erythropoietin release. The industrial production of boldenone mainly relies on chemical synthesis, which has various problems, such as a complex conversion process, excessive byproducts, and serious environmental pollution. Therefore, it is of great significance to explore a new biosynthetic route. Recently, the enzymatic synthesis of steroid compounds has been performed more frequently than in the past. In this work, boldenone was produced from androstenedione (AD) in two steps by a dual-enzyme cascade of 17β-hydroxysteroid dehydrogenase (17β-HSD) and 3-sterone-Δ1-dehydrogenase (KstD). The conversion efficiency of three isoenzymes of 17β-HSD from Mycobacterium sp. LY-1 for substrate AD was first analyzed. After that, the 17β-HSD2 with high selectivity and specificity for AD was screened and co-expressed with KstD3 in Escherichia coli BL21 to construct a dual-enzyme catalytic system. The results showed that the synthesis of boldenone from AD could be achieved by constructing the dual-enzyme expression system of 17β-HSD and KstD, as we determined that the concentration of boldenone reached 24.3 mg/L. To further improve the synthesis efficiency of boldenone, the expression conditions of the dual-enzyme system were optimized, and the concentration of boldenone reached 31.9 mg/L. The exploration of this route will provide a foundation for the efficient enzymatic synthesis of boldenone.
In recent years, the control of plant pests and diseases has faced new eco-friendly protocols and the use of biocontrol is an attractive alternative as a green and safer management strategy. The use of biological control agents (BCAs) is a major emerging tool in the field of crop disease or pest management that provides an opportunity to replace chemical pesticides that promote sustainable agriculture. Trichoderma species are one of the most efficient BCAs, and the search for new, more bioactive, virulent, and efficient species is a permanent task. In the present study, the potential for biocontrol of four strains of the Trichoderma genus isolated from Coahuila semi-desert was evaluated. The evaluated criteria were: radial growth, growth velocity, and growth rate, as well as the PDA sporulation level. The T1DIA-RRG strain achieves maximum growth at 60 h in radial growth, and a growth rate of 0.60 mm/h in antagonist assays, while T4DIA-ARG strain generates the major spore production (1 × 108 spores/g). In addition, a solid-state fermentation process with sugar cane bagasse is proposed to develop biotechnological strategies for biological control agents, which show satisfactory results for fungal strain Trichoderma asperellum T4DIA-ARD with the required spore production level to be considered and used as a greenhouse biocontrol agent.
The presence of various furan aldehydes in cellulose hydrolysate affects the fermentation of 1,2,4-butanetriol (BT) in a similar way. In this study, furfural was used as a representative for the modification of BT-producing E. coli for tolerance. The engineered Escherichia coli harboring the recombinant BT pathway had decreased the biomass by 58% and the BT titer by 52% in the presence of 0.4 g/L furfural. To improve the tolerance of the strain and the efficiency of BT synthesis in the hydrolysate, seven furfural tolerance genes, ucpA, fucO, groESL, lpcA, pncB, nadD, and nadE were introduced into the BT-producing E. coli. All these genes differentially improved the furfural tolerance performance of the cells. Overexpression of these tolerance genes reduces the accumulation of reactive oxygen species and promotes glycolysis. Oxidoreductase UcpA was the best candidate for improving cell growth. UcpA also increased the activities of Xdh and YqhD and the RNA levels of YjhG and KivD, leading to a 32% increase in BT yield per biomass and the best BT titer of 14.4 g/L in the presence of 0.4 g/L furfural. In the shaker and 5 L fermenter, the BT titer reached 5.2 g/L and 11.2 g/L, respectively, by using corn cob cellulose as substrate.
l-Threonine is an important amino acid, which can be added in food, medicine or feed. In this paper, an l-threonine-producing strain was constructed using a modified CRISPR gene editing technology. Here, it was verified that the mutation of glycine at position 433 of aspartate kinase AKI to arginine (thrA G1297A) relieve effectively the feedback inhibition of AKI by l-threonine. The trc promoter replaced the native promoter of thrA in the Escherichia coli XQ-12 genome, and thus increasing its expression level. Moreover, by modifying the glycolytic pathway, disruption of phosphofructokinase encoded by the gene pfkA and pyruvate kinase encoded by the gene pykF increased l-threonine production. Then, the ppc gene encoding phosphoenolpyruvate carboxylase was overexpressed by replacing its native promoter with the core-trc promoter, which slightly improved the growth of the l-threonine-producing strain E. coli XQ-12 as well as the l-threonine production. In addition, it was found that further absence of the gene crr in the PTS system and the gene tdh encoding threonine dehydrogenase improved significantly l-threonine production. The final amounts of l-threonine produced by plasmid-free, antibiotic-free and inducer-free strains E. coli XQ-12.4 were 127.3 g/L and 3.536 g/L/h, respectively, in fed-batch fermentation.
(2R,3R)-BDO is an important bio-based four-carbon platform compound and widely used in chemical, food, pharmaceutical, fuel and aerospace fields. Serratia marcescens has been shown to be an effective strain for producing BDO. However, there have been few reports on the metabolic engineering of this strain to efficiently produce (2R,3R)-BDO using xylose. In this study, the endogenous strong promoter was screened and modified, and combined with the screened RBS. (2R,3R)-BDO was successfully produced by combining the selected promoters and RBS with the overexpressed key enzymes (ALS, ALSD, BDH, GLF) of (2R,3R)-BDO production. The optimum fermentation temperature and pH were 37 ℃ and 6.0, respectively, and the optimized yield reached 6.0 g/L. After batch fermentation, the (2R,3R)-BDO yield reached 36.6 g/L. This provided a good idea for efficient production of (2R,3R)-BDO from xylose.