Strategy for efficiently utilizing Escherichia coli cells producing isobutanol by combining isobutanol and indigo production systems

Knockout of the Agrobacterium ILVC gene generates a valine-isoleucine auxotrophic strain for plant transformation

The Agrobacterium tumefaciens mediated transformation is the prevailing methodology for plant genetic manipulation; however, A. tumefaciens overgrowth is a common constraint in the process. Exploring auxotrophic A. tumefaciens could reduce overgrowth and enhance plant transformation efficiency. The ILVC gene, which encodes the ketol-acid isomeroreductase, is critical for Valine (Val) and isoleucine (Ile) biosynthesis in some microorganisms. However, its function in A. tumefaciens is unclear. To ascertain the function of ILVC and generate an auxotrophic A. tumefaciens, this study employed an allelic exchange to disrupt the ILVC in A. tumefaciens strain GV3101. This resulted in the loss of ketol-acid isomeroreductase activity and the prevention of Val and Ile biosynthesis, creating a dual-auxotrophic GV3101∆ILVC. Transient expression assays in Nicotiana benthamiana transformation demonstrated that the GV3101∆ILVC was capable of T-DNA transfer. Moreover, stable genetic transformation analysis in N. benthamiana indicated that the introduction of GV3101∆ILVC led to a reduction in overgrowth within infected plant tissues. Additionally, an enhancement in transformation efficiency was observed with the prolongation of the co-cultivation time of the explant-infected strain. This study revealed the function of ILVC and explored a dual-auxotrophic A. tumefaciens for Val and Ile, potentially broadening the utilization of auxotrophic strains in plant genetic transformation.

Enhancement of Indigo Production by a Metabolically Engineered Escherichia coli MG1655 Using Membrane Engineering and Two-Stage Cultivation

Indigo, a natural blue pigment extensively used in the food and textile industries, faces sustainability challenges due to toxic chemicals in its industrial synthesis. In this study, an efficient E. coli MG1655 system was developed for indigo biosynthesis. The strain was engineered by genomic integration and plasmid-based expression of Methylophaga aminisulfidivorans flavin-containing monooxygenase (MaFMO) and endogenous tryptophanase (TnaA). To optimize metabolic flux toward indigo production, key competitive pathway genes were deleted, and membrane engineering genes were introduced to alleviate toxicity and improve product secretion. A two-stage fermentation strategy with controlled feeding of the tryptophan substrate and surfactants further optimized indigo production. The integrated approach achieved a maximum indigo titer of 3.9 g/L in 5 L of fed-batch fermentation. This study highlights the successful integration of genetic engineering and fermentation strategies to enhance microbial indigo production, offering a green alternative to chemical synthesis with potential applications in food-grade colorant production and the textile industries.

Efficient carbon flux allocation towards D-pantothenic acid production via growth-decoupled strategy in Escherichia coli

For industrial strain construction, rational allocation of carbon flux is of paramount importance especially for decoupling cell growth and chemical productions to get maximum titer, rate, yield (TRY), which become Gordian Knot. Here, a temperature-sensitive switch and genetic circuits was used for effectively decoupling cell growth from D-pantothenic acid (DPA) production, along with systematically metabolic engineering including blocking redundant pathways of pyruvate and enhancing DPA driving force. Afterwards, rapid biomass accumulation only happened during growth stage, and subsequent high-efficient DPA production was initiated with reducing fermentation temperature. Finally, 97.20 g/L DPA and 0.64 g/g glucose conversion rate were achieved in 5-liter fed-batch fermentation. These undisputedly represent a milestone for the biosynthesis of DPA. With using strategies for decoupling cell growth from chemical productions, it would serve as "Alexander's sword" to cut Gordian Knot to get industrial chassis cells with excellent TRY for de novo biosynthesis of valuable chemicals.

Production of bio-indigo from engineered Pseudomonas putida KT2440 harboring tryptophanase and flavin-containing monooxygenase

Indigo is a unique blue dye that has been used in the textile industry for centuries and is currently mass-produced commercially through chemical synthesis. However, the use of toxic substrates and reducing agents for chemical synthesis is associated with environmental concerns, necessitating the development of eco-friendly alternatives based on microbial production. In this study, a robust industrial strategy for indigo production was developed using Pseudomonas putida KT2440 as the host strain, which is characterized by its excellent ability to degrade aromatic compounds and high resistance to environmental stress. By introducing the genes tryptophanase (tnaA) and Flavin-containing monooxygenase (FMO), a P. putida HI201 strain was constructed to produce indigo from tryptophan. To enhance the indigo yield, culture conditions, including medium composition, temperature, tryptophan concentration, and shaking speed, were optimized. Under optimal conditions such as TB medium, 15 mM tryptophan, 30°C, 200 rpm, P. putida HI201 biosynthesized 1.31 g/L indigo from tryptophan in a fed-batch fermentation system. The introduction of tnaA and FMO genes also enabled the production of indigo in various P. putida species, and the indigo-producing strain had a blue color, which served as a visual indicator. This study presents a strategy for using P. putida as a host for robust and sustainable microbial production of indigo, highlighting the strain's applicability and efficiency in environment friendly dye synthesis.

Overview of indigo biosynthesis by Flavin-containing Monooxygenases: History, industrialization challenges, and strategies

Indigo is a natural dye extensively used in the global textile industry. However, the conventional synthesis of indigo using toxic compounds like aniline, formaldehyde, and hydrogen cyanide has led to environmental pollution and health risks for workers. This method also faces growing economic, sustainability, and environmental challenges. To address these issues, the concept of bio-indigo or indigo biosynthesis has been proposed as an alternative to aniline-based indigo synthesis. Among various enzymes, Flavin-containing Monooxygenases (FMOs) have shown promise in achieving a high yield of bio-indigo. However, the industrialization of indigo biosynthesis still encounters several challenges. This review focuses on the historical development of indigo biosynthesis mediated by FMOs. It highlights several factors that have hindered industrialization, including the use of unsuitable chassis (Escherichia coli), the toxicity of indole, the high cost of the substrate L-tryptophan, the water-insolubility of the product indigo, the requirement of reducing reagents such as sodium dithionite, and the relatively low yield and high cost compared to chemical synthesis. Additionally, this paper summarizes various strategies to enhance the yield of indigo synthesized by FMOs, including redundant sequence deletion, semi-rational design, cheap precursor research, NADPH regeneration, large-scale fermentation, and enhancement of water solubility of indigo.

Tryptophan-Based Hyperproduction of Bioindigo by Combinatorial Overexpression of Two Different Tryptophan Transporters

Indigo is a valuable, natural blue dye that has been used for centuries in the textile industry. The large-scale commercial production of indigo relies on its extraction from plants and chemical synthesis. Studies are being conducted to develop methods for environment-friendly and sustainable production of indigo using genetically engineered microbes. Here, to enhance the yield of bioindigo from an E. coli whole-cell system containing tryptophanase (TnaA) and flavin-containing monooxygenase (FMO), we evaluated tryptophan transporters to improve the transport of aromatic compounds, such as indole and tryptophan, which are not easily soluble and passable through cell walls. Among the three transporters, Mtr, AroP, and TnaB, AroP enhanced indigo production the most. The combination of each transporter with AroP was also evaluated, and the combination of AroP and TnaB showed the best performance compared to the single transporters and two transporters. Bioindigo production was then optimized by examining the culture medium, temperature, isopropyl β-D-1-thiogalactopyranoside concentration, shaking speed (rpm), and pH. The novel strain containing aroP and tnaB plasmid with tnaA and FMO produced 8.77 mM (2.3 g/l) of bioindigo after 66 h of culture. The produced bioindigo was further recovered using a simple method and used as a watercolor dye, showing good mixing with other colors and color retention for a relatively long time. This study presents an effective strategy for enhancing indigo production using a combination of transporters.

Indigo production goes green: a review on opportunities and challenges of fermentative production

Indigo is a widely used dye in various industries, such as textile, cosmetics, and food. However, traditional methods of indigo extraction and processing are associated with environmental and economic challenges. Fermentative production of indigo using microbial strains has emerged as a promising alternative that offers sustainability and cost-effectiveness. This review article provides a critical overview of microbial diversity, metabolic pathways, fermentation strategies, and genetic engineering approaches for fermentative indigo production. The advantages and limitations of different indigo production systems and a critique of the current understanding of indigo biosynthesis are discussed. Finally, the potential application of indigo in other sectors is also discussed. Overall, fermentative production of indigo offers a sustainable and bio-based alternative to synthetic methods and has the potential to contribute to the development of sustainable and circular biomanufacturing.