Selection method of pH conditions to establish Pseudomonas taetrolens physiological states and lactobionic acid production

Microbial physiological responses resulting from inappropriate bioprocessing conditions may have a marked impact on process performance within any fermentation system. The influence of different pH-control strategies on physiological status, microbial growth and lactobionic acid production from whey by Pseudomonas taetrolens during bioreactor cultivations has been investigated for the first time in this work. Both cellular behaviour and bioconversion efficiency from P. taetrolens were found to be negatively influenced by pH-control modes carried out at values lower than 6.0 and higher than 7.0. Production schemes were also influenced by the operational pH employed, with asynchronous production from damaged and metabolically active subpopulations at pH values lower than 6.0. Moreover, P. taetrolens showed reduced cellular proliferation and a subsequent delay in the onset of the production phase under acidic conditions (pH?<?6.0). Unlike cultivations performed at 6.5, both pH-shift and pH-stat cultivation strategies performed at pH values lower than 6.0 resulted in decreased lactobionic acid production. Whereas the cellular response showed a stress-induced physiological response under acidic conditions, healthy functional cells were predominant at medium operational pH values (6.5–7.0). P. taetrolens thus displayed a robust physiological status at initial pH value of 6.5, resulting in an enhanced bioconversion yield and lactobionic acid productivity (7- and 4-fold higher compared to those attained at initial pH values of 4.5 and 5.0, respectively). These results have shown that pH-control modes strongly affected both the physiological response of cells and the biological performance of P. taetrolens, providing key information for bio-production of lactobionic acid on an industrial scale.     

Microbial production of specialty organic acids from renewable and waste materials

Microbial production of organic acids has become a fast-moving field due to the increasing role of these compounds as platform chemicals. In recent years, the portfolio of specialty fermentation-derived carboxylic acids has increased considerably, including the production of glyceric, glucaric, succinic, butyric, xylonic, fumaric, malic, itaconic, lactobionic, propionic and adipic acid through innovative fermentation strategies. This review summarizes recent trends in the use of novel microbial platforms as well as renewable and waste materials for efficient and cost-effective bio-based production of emerging high-value organic acids. Advances in the development of robust and efficient microbial bioprocesses for producing carboxylic acids from low-cost feedstocks are also discussed. The industrial market scenario is also reviewed, including the latest information on the stage of development for producing these emerging bio-products via large-scale fermentation.     

Development of GRAS strains for nutraceutical production using systems and synthetic biology approaches: advances and prospects

Nutraceuticals are food substances with medical and health benefits for humans. Limited by complicated procedures, high cost, low yield, insufficient raw materials, resource waste, and environment pollution, chemical synthesis and extraction are being replaced by microbial synthesis of nutraceuticals. Many microbial strains that are generally regarded as safe (GRAS) have been identified and developed for the synthesis of nutraceuticals, and significant nutraceutical production by these strains has been achieved. In this review, we systematically summarize recent advances in nutraceutical research in terms of physiological effects on health, potential applications, drawbacks of traditional production processes, characteristics of production strains, and progress in microbial fermentation. Recent advances in systems and synthetic biology techniques have enabled comprehensive understanding of GRAS strains and its wider applications. Thus, these microbial strains are promising cell factories for the commercial production of nutraceuticals.     

Microbial amensalism in Lactobacillus casei and Pseudomonas taetrolens mixed culture

Pseudomonas taetrolens has recently been revealed as an effective microbial producer of lactobionic acid from carbohydrates contained in dairy byproducts. In terms of food industrial applications, the implementation of lactobionic acid biosynthesis coupled with the classic bacterial production of lactic acid appears an important goal. This research paper studies the simultaneous fermentation of residual cheese whey by P. taetrolens and Lactobacillus casei to co-produce lactic and lactobionic acids. Experimental data showed the importance of the interactions established between the two microorganisms. Changes in physiology, viability, growth, and productive capacity were tested experimentally. Lactobacillus was not seen to suffer any appreciable stress, but considerable variations were observed in the Pseudomonas behavior presumably owing to inhibitory lactic metabolites, interaction that can be classified as microbial amensalism. As to production, lactic acid remained without significant changes in mixed fermentations, whereas the production of lactobionic acid decreased sharply due to the competitive exclusion of Pseudomonas.

     

Dynamic control in metabolic engineering: Theories,tools, and applications

Metabolic engineering has allowed the production of a diverse number of valuable chemicals using microbial organisms. Many biological challenges for improving bio-production exist which limit performance and slow the commercialization of metabolically engineered systems. Dynamic metabolic engineering is a rapidly developing field that seeks to address these challenges through the design of genetically encoded metabolic control systems which allow cells to autonomously adjust their flux in response to their external and internal metabolic state. This review first discusses theoretical works which provide mechanistic insights and design choices for dynamic control systems including two-stage, continuous, and population behavior control strategies. Next, we summarize molecular mechanisms for various sensors and actuators which enable dynamic metabolic control in microbial systems. Finally, important applications of dynamic control to the production of several metabolite products are highlighted, including fatty acids, aromatics, and terpene compounds. Altogether, this review provides a comprehensive overview of the progress, advances, and prospects in the design of dynamic control systems for improved titer, rate, and yield metrics in metabolic engineering.     

Biosynthesis and biotechnological production of degradable polyhydroxyalkanoic acid

The use of biodegradable polymers is one of the key solution to environmental problems and the development of biocompatible material. The impact of such a large commercial opportunity is one of the primary reasons for much interest in the field of microbial polyester, polyhydroxyalkanoic acid (PHA). Its valuable properties of biodegradability, biocompatibility and thermoplasticity have attracted considerable commercial interest, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] has been launched as the first market product. Recent advances in molecular genetics and microbial physiology of PHA biosynthesis have been uncovering the biosynthetic mechanics at molecular level, and extensive efforts for the developments of practical applications and cost-effective mass production of PHA will profell the commercialization of PHA towards the commodity market for biodegradable plastics. The biosynthesis of new members of PHA family with new monomer or unusual composition will also lead to the biotechnological production of tailor-made biopolymer for various applications.     

大肠杆菌生产异戊二烯的代谢工程研究进展

异戊二烯作为一种重要的化工原料,主要用于合成橡胶。此外,还广泛应用于医药或化工中间体、食品、粘合剂及航空燃料等领域。利用微生物法生产异戊二烯因具有环境友好、利用廉价的可再生原料、可持续发展等优势而成为当今研究的热点。这里介绍了大肠杆菌生产异戊二烯的代谢途径及关键酶,从代谢工程的角度出发综述了目前为提高大肠杆菌异戊二烯产量所应用到的方法和策略,并对今后的发展方向进行了展望。     

Physiological heterogeneity of Pseudomonas taetrolens during lactobionic acid production

Physiological heterogeneity constitutes a critical parameter in biotechnological systems since both metabolite yield and productivity are often hampered by the presence of undesired physiological cell subpopulations. In the present study, the physiological status and functionality of Pseudomonas taetrolens cells were monitored by multiparameter flow cytometry during fermentative lactobionic acid production at the shake-flask and bioreactor scale. In shake-flask fermentation, the onset of the lactobionic acid production phase was accompanied by a progressive loss of cellular metabolic activity, membrane polarization, and membrane integrity concomitantly to acidification. In fact, population dynamics has shown the prevalence of damaged and dead subpopulations when submitted to a pH?<?4 from 16?h onwards. Furthermore, fluorescence-activated cell sorting revealed that these sublethally injured cells were nonculturable. In contrast, P. taetrolens cells exhibited a robust physiological status during bioreactor cultivations performed with a pH-shifted strategy at 6.5, remaining predominantly healthy and metabolically active (>96?%) as well as maintaining bioconversion efficiency throughout the course of the fermentation. Additionally, an assessment of the seed culture’s physiological robustness was carried out in order to determine the best seed culture age. Results showed that bioreactor culture performance, growth, and lactobionic acid production efficiency were strongly dependent on the physiological heterogeneity displayed by the seed culture. This study provides the most suitable criteria for optimizing lactobionic acid production efficiency through a novel flow cytometric-based approach based on the physiological status of P. taetrolens. It also constitutes a valuable, broad-ranging methodology for the enhancement of microbial bioprocesses involved in the production of secondary metabolites.     

非天然氨基酸细胞工厂的构建与应用

非天然氨基酸在医药、农药、材料等领域得到广泛应用,其绿色、高效合成越来越受到关注.近年来,随着合成生物学的快速发展,微生物细胞工厂为非天然氨基酸的制造提供了重要手段.文中从合成途径的重构、关键酶的设计改造及与前体的协同调控、竞争性旁路途径的敲除、辅因子循环系统的构建等方面介绍了 一系列非天然氨基酸细胞工厂构建与应用的研...     

Production and mass transfer characteristics of non-Newtonian biopolymers for biomedical applications

The market for microbial biopolymers is currently expanding to include several emerging biomedical applications. Specifically, these applications are drug delivery and wound healing. A fundamental understanding of the key fermentation parameters is necessary in order to optimize the production of these biopolymers. Considering that most microbial biopolymer systems exhibit non-Newtonian rheology, oxygen mass transfer can be an important parameter to optimize and control. In this article, we present a critical review of recent advances in rheological and mass transfer characteristics of selected biopolymers of commercial interest in biomedical applications.     

Recent advances in production of 5-aminolevulinic acid using biological strategies

5-Aminolevulinic acid (5-ALA) is the precursor for the biosynthesis of tetrapyrrole compounds and has broad applications in the medical and agricultural fields. Because of the disadvantages of chemical synthesis methods, microbial production of 5-ALA has drawn intensive attention and has been regarded as an alternative in the last years, especially with the rapid development of metabolic engineering and synthetic biology. In this mini-review, recent advances on the application and microbial production of 5-ALA using novel biological approaches (such as whole-cell enzymatic-transformation, metabolic pathway engineering and cell-free process) are described and discussed in detail. In addition, the challenges and prospects of synthetic biology are discussed.     

Process challenges relating to hematopoietic stem cell cultivation in bioreactors

Hematopoietic stem cells (HSCs) are extremely useful in treating a wide range of diseases and have a variety of useful research applications. However, the routinely generated low in vitro concentrations of HSCs from current bioreactor manufacturing systems has been a hindrance to the full-scale application of these essential cellular materials. This has made the search for novel bioreactor systems for high-concentration HSC production a major research endeavour. This review addresses process challenges in relation to bioreactor development and optimisation for high-density HSC production under effective monitoring of essential culture parameters, such as pH, dissolved oxygen and nutrient uptake. It discusses different process strategies and bioreactor configurations for HSCs production from a commercial viability perspective, and also discusses recent advances in the field.     

Metabolic engineering for the synthesis of polyesters: A 100-year journey from polyhydroxyalkanoates to non-natural microbial polyesters

As concerns increase regarding sustainable industries and environmental pollutions caused by the accumulation of non-degradable plastic wastes, bio-based polymers, particularly biodegradable plastics, have attracted considerable attention as potential candidates for solving these problems by substituting petroleum-based plastics. Among these candidates, polyhydroxyalkanoates (PHAs), natural polyesters that are synthesized and accumulated in a range of microorganisms, are considered as promising biopolymers since they have biocompatibility, biodegradability, and material properties similar to those of commodity plastics. Accordingly, substantial efforts have been made to gain a better understanding of mechanisms related to the biosynthesis and properties of PHAs and to develop natural and recombinant microorganisms that can efficiently produce PHAs comprising desired monomers with high titer and productivity for industrial applications.Recent advances in biotechnology, including those related to evolutionary engineering, synthetic biology, and systems biology, can provide efficient and effective tools and strategies that reduce time, labor, and costs to develop microbial platform strains that produce desired chemicals and materials. Adopting these technologies in a systematic manner has enabled microbial fermentative production of non-natural polyesters such as poly(lactate) [PLA], poly(lactate-co-glycolate) [PLGA], and even polyesters consisting of aromatic monomers from renewable biomass-derived carbohydrates, which can be widely used in current chemical industries.In this review, we present an overview of strain development for the production of various important natural PHAs, which will give the reader an insight into the recent advances and provide indicators for the future direction of engineering microorganisms as plastic cell factories. On the basis of our current understanding of PHA biosynthesis systems, we discuss recent advances in the approaches adopted for strain development in the production of non-natural polyesters, notably 2-hydroxycarboxylic acid-containing polymers, with particular reference to systems metabolic engineering strategies.     

A comprehensive review of microbial electrochemical systems as a platform technology

Microbial electrochemical systems (MESs) use microorganisms to covert the chemical energy stored in biodegradable materials to direct electric current and chemicals. Compared to traditional treatment-focused, energy-intensive environmental technologies, this emerging technology offers a new and transformative solution for integrated waste treatment and energy and resource recovery, because it offers a flexible platform for both oxidation and reduction reaction oriented processes. All MESs share one common principle in the anode chamber, in which biodegradable substrates, such as waste materials, are oxidized and generate electrical current. In contrast, a great variety of applications have been developed by utilizing this in situ current, such as direct power generation (microbial fuel cells, MFCs), chemical production (microbial electrolysis cells, MECs; microbial electrosynthesis, MES), or water desalination (microbial desalination cells, MDCs). Different from previous reviews that either focus on one function or a specific application aspect, this article provides a comprehensive and quantitative review of all the different functions or system constructions with different acronyms developed so far from the MES platform and summarizes nearly 50 corresponding systems to date. It also provides discussions on the future development of this promising yet early-stage technology.     

Efficient lactobionic acid production from whey by Pseudomonas taetrolens under pH-shift conditions

Lactobionic acid finds applications in the fields of pharmaceuticals, cosmetics and medicine. The production of lactobionic acid from whey by Pseudomonas taetrolens was studied in shake-flasks and in a bioreactor. Shake-flask experiments showed that lactobionic acid was a non-growth associated product. A two-stage pH-shift bioconversion strategy with a pH-uncontrolled above 6.5 during the growth phase and maintained at 6.5 during cumulative production was adopted in bioreactor batch cultures. An inoculation level of 30% promoted high cell culture densities that triggered lactobionic acid production at a rate of 1.12 g/Lh. This methodology displayed efficient bioconversion with cheese whey as an inexpensive substrate for lactobionic acid production.     

Economical challenges to microbial producers of butanol: feedstock, butanol ratio and titer

Butanol is an important solvent and transport fuel additive, and can be produced by microbial fermentation. Attempts to generate a superior microbial producer of butanol have been made through different metabolic engineering strategies. However, to date, butanol bio-production is still not economically competitive compared to petrochemical-derived production because of its major drawbacks, such as, high cost of the feedstocks, low butanol concentration in the fermentation broth and the co-production of low-value by-products acetone and ethanol. Here we analyze the main bottlenecks in microbial butanol production and summarize relevant advances from recently reported studies. Further needs and directions for developing real industrially applicable strains in butanol production are also discussed.     

Production and Mass Transfer Characteristics of Non-Newtonian Biopolymers for Biomedical Applications

ABSTRACT:?

The market for microbial biopolymers is currently expanding to include several emerging biomedical applications. Specifically, these applications are drug delivery and wound healing. A fundamental understanding of the key fermentation parameters is necessary in order to optimize the production of these biopolymers. Considering that most microbial biopolymer systems exhibit non-Newtonian rheology, oxygen mass transfer can be an important parameter to optimize and control. In this article, we present a critical review of recent advances in rheological and mass transfer characteristics of selected biopolymers of commercial interest in biomedical applications.     

Expanding horizons of shikimic acid

Shikimic acid is an industrially important chiral compound used as a key ingredient in formulation of drug Oseltamivir phosphate (Tamiflu) for the treatment of swine/avian flu. The high cost and limited availability of shikimic acid isolated from plants has detained the use of this valuable building block of the drug. It is a versatile compound having many characteristic properties for many synthetic reactions particularly in pharmaceuticals and cosmetic industries. By virtue of being a natural product, the relevant biochemical pathway in microorganisms can be harnessed into fermentation processes to produce shikimic acid. This is an excellent alternative for the sustainable and efficient production of shikimic acid over the tedious and cumbersome process of plant based extraction methods. Various strategies of shikimic acid production are reviewed and an account of comparison of their challenges, promises and restraint is presented. Furthermore, present review attempts to focus on the market trend of shikimic acid due to its high demand with particular emphasis laid on the pandemics of swine flu. This review not only covers the recent advances in shikimic acid production but also highlights the versatile applications and its market scenario. The concluding remarks and its potential as a commercial bulk chemical are discussed in the light of current research.     

Biotechnological production of muconic acid: current status and future prospects

Muconic acid (MA), a high value-added bio-product with reactive dicarboxylic groups and conjugated double bonds, has garnered increasing interest owing to its potential applications in the manufacture of new functional resins, bio-plastics, food additives, agrochemicals, and pharmaceuticals. At the very least, MA can be used to produce commercially important bulk chemicals such as adipic acid, terephthalic acid and trimellitic acid. Recently, great progress has been made in the development of biotechnological routes for MA production. This present review provides a comprehensive and systematic overview of recent advances and challenges in biotechnological production of MA. Various biological methods are summarized and compared, and their constraints and possible solutions are also described. Finally, the future prospects are discussed with respect to the current state, challenges, and trends in this field, and the guidelines to develop high-performance microbial cell factories are also proposed for the MA production by systems metabolic engineering.     

工业乳酸发酵的近期进展

乳酸是一种重要的多用途有机酸。通过菌种改良和发酵工艺技术的改进,可以大大提升微生物发酵技术水平,降低成本。简要综述有关的研究进展。