🧬 biology

Autochthonous bioaugmentation with Pediococcus pentosaceus MZ-4 enhances indigoid production by accelerating indican biotransformation and remodeling the fermentation microbiome

This study demonstrates that autochthonous bioaugmentation with *Pediococcus pentosaceus* MZ-4 significantly enhances Indigo Naturalis production by accelerating indican biotransformation via β-glucosidase activity and remodeling the fermentation microbiome toward a stable, lactic acid bacteria-dominated community.

Original authors: Xin Yang, Fangyu Xiang, Yun Duan, Qi Huang, Ming Yang, Xiangbo Yang, Hongya Yang, Li Han, Dingkun Zhang, Yanan He

Published 2026-09-18

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Xin Yang, Fangyu Xiang, Yun Duan, Qi Huang, Ming Yang, Xiangbo Yang, Hongya Yang, Li Han, Dingkun Zhang, Yanan He

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

For centuries, artisans have relied on a quiet, unpredictable transformation to create the deep blue dye found in denim and the medicinal compounds used to treat certain blood disorders. This process begins with the leaves of the indigo plant, which are soaked in water to start a fermentation. In this watery environment, naturally occurring microbes work to break down a colorless chemical hidden inside the leaves, turning it into the vibrant blue pigment known as indigo. While this method has produced beautiful dyes and life-saving medicines for generations, it has always been a gamble. The process is slow, often taking days to complete, and the results vary wildly from one batch to the next because the specific microbes doing the work are unknown and uncontrolled. Scientists have long suspected that if they could identify the specific bacteria responsible for this chemical change and encourage them to take charge, they could make the process faster, more reliable, and more productive.

A team of researchers set out to solve this puzzle by looking closely at the microscopic world inside a traditional fermentation vat. They began by collecting samples from the soaking liquid and searching for the specific bacteria that produce an enzyme capable of unlocking the plant's chemical potential. After isolating dozens of different strains, they found a standout candidate: a round, single-celled bacterium named Pediococcus pentosaceus MZ-4. This strain was special because it produced high levels of a specific tool, an enzyme called beta-glucosidase, which acts like a pair of molecular scissors. Its job is to snip a sugar molecule off a precursor chemical called indican, releasing a reactive compound that eventually turns into the blue pigment. The researchers tested this strain and found that it worked efficiently at the temperatures and acidity levels typical of the traditional process, making it a perfect fit for the job.

To ensure this bacterium could work at its peak, the scientists first fine-tuned the conditions under which it grew. They adjusted the temperature, the acidity of the water, and the amount of bacteria added to the mix, discovering that a slightly acidic environment around pH 6.0 and a temperature near 30 degrees Celsius allowed the strain to produce the most enzymes. Under these optimized conditions, the bacteria generated a powerful amount of the necessary enzyme, far more than they produced under standard conditions. With this powerful strain ready, the team moved to the main event: testing whether adding this specific bacterium to a traditional fermentation vat would actually improve the outcome compared to leaving nature to take its course.

The results were striking. When the researchers introduced the Pediococcus pentosaceus MZ-4 strain into the fermentation tank, the entire process sped up significantly. The traditional method, which relies on a chaotic mix of many different microbes, usually takes a long time to shift from a clear liquid to a deep blue-green color. In the tanks inoculated with the new strain, this color change happened about twelve hours faster. The leaves broke down more quickly, and the chemical transformation happened with greater urgency. By the end of the process, the tanks treated with the specific strain contained nearly 47 percent more indigo and nearly 58 percent more of a related red-purple compound called indirubin than the traditional batches. These two compounds are the valuable active ingredients sought after for both their color and their medicinal properties.

The success of this approach lies in how the new strain reshaped the entire community of life in the vat. In a traditional fermentation, many different types of bacteria compete, leading to a messy and unpredictable environment. When the researchers added the Pediococcus strain, it acted as a leader, quickly changing the environment by making the water more acidic and removing oxygen. These changes created a hostile environment for the other, less helpful bacteria, while allowing the Pediococcus and a few related beneficial bacteria to take over. This shift created a stable, organized community dominated by lactic acid bacteria, which are known for their ability to break down plant sugars efficiently. The researchers confirmed that this new, orderly community was directly linked to the faster production of the blue and red pigments.

To understand exactly how this bacterium was able to perform such a feat, the scientists mapped out its entire genetic code. They found that the strain's DNA is packed with instructions for building enzymes that break down carbohydrates, specifically a large family of tools known as glycoside hydrolases. Among these, the genes responsible for the beta-glucosidase enzyme were particularly abundant. This genetic evidence confirmed that the bacterium is naturally equipped with the machinery needed to cut the sugar off the indican molecule, releasing the precursor needed to make the dye. The study did not just find a faster way to make dye; it revealed the biological mechanism behind the transformation, showing that a single, well-chosen microbe can guide a complex chemical process.

This work offers a clear path forward for modernizing an ancient practice. By identifying and adding a specific, native bacterium to the fermentation process, producers can move away from the uncertainty of spontaneous fermentation. Instead of waiting for the right mix of wild microbes to appear, they can introduce a known, reliable worker that accelerates the reaction and ensures a higher yield of the desired products. The findings suggest that this method of "bioaugmentation," or boosting a system with a helpful microbe, can make the production of natural indigo and its medicinal derivatives more efficient and consistent, preserving the value of these natural resources while reducing the time and waste associated with traditional methods.

Technical Summary: Autochthonous Bioaugmentation with Pediococcus pentosaceus MZ-4 for Enhanced Indigoid Production

Problem Statement
The traditional production of Indigo Naturalis (Qingdai), a critical component in treating chronic myeloid leukemia, relies on spontaneous soaking fermentation of Strobilanthes cusia leaves. This process is characterized by long fermentation cycles, uncontrollable microbial succession, significant batch-to-batch variation, and low yields of active ingredients (indigo and indirubin). The inefficiencies stem largely from the undefined roles of indigenous microbes and the lack of controlled enzymatic conversion of the precursor indican. While exogenous $\beta$ -glucosidase supplementation has been attempted, it suffers from high costs, poor source traceability, and limited adaptability to complex open fermentation environments. Consequently, there is a need for a sustainable strategy utilizing indigenous functional strains to direct microbial succession and enhance bioconversion efficiency.

Methodology
The study employed a multi-stage approach to isolate, characterize, and apply an indigenous functional strain:

Strain Isolation and Screening: Microorganisms were isolated from spontaneous S. cusia fermentation broth. Initial screening utilized an aesculin-ferric ammonium citrate chromogenic assay to identify $\beta$ -glucosidase producers. Quantitative screening using the p-nitrophenyl- $\beta$ -D-glucopyranoside (PNPG) method identified five high-yield strains.
Strain Characterization: The five top strains underwent morphological, biochemical, and molecular (16S rRNA/ITS sequencing) identification. Enzymatic properties, including optimal temperature, pH, thermal stability, and kinetic parameters ( $K_m$ , $V_{max}$ ) for indican hydrolysis, were evaluated to select the most suitable candidate for the fermentation environment (typically 30°C, pH 5.5–7.5).
Mechanistic Analysis: The selected strain was tested for its ability to degrade indican and produce indigo/indirubin. Metabolomic profiling (HPLC-MS/MS) was conducted to map the degradation pathway and identify intermediates.
Process Optimization: Single-factor experiments and Response Surface Methodology (Box-Behnken design) were used to optimize fermentation conditions (temperature, initial pH, inoculum size) for maximum $\beta$ -glucosidase production.
Bioaugmentation and Comparative Fermentation: The optimized strain was inoculated into a natural fermentation system (MZ-4F group) and compared against a natural fermentation control (NF group). Parameters monitored included physicochemical changes (pH, dissolved oxygen, ORP), microbial community structure (16S rRNA amplicon sequencing), and metabolite accumulation.
Genomic Analysis: Whole-genome sequencing (Illumina and Oxford Nanopore) and bioinformatics annotation (COG, GO, KEGG, CAZy) were performed to elucidate the genetic basis of the strain's enzymatic capabilities.

Key Results

Strain Identification: Strain MZ-4 was identified as Pediococcus pentosaceus. It exhibited a Gram-positive coccus morphology and demonstrated superior suitability for the fermentation process, with optimal activity at 40°C and pH 6.0, and high stability within the fermentation range.
Enzymatic Kinetics: MZ-4 displayed high substrate affinity for indican ( $K_m$ values indicated strong binding). It degraded over 83.7% of indican within 12 hours, converting it into indigo and indirubin via a proposed pathway involving $\beta$ -glucosidase-mediated hydrolysis to indoxyl, followed by oxidative dimerization and cyclization.
Process Optimization: Through Response Surface Methodology, fermentation conditions were optimized to an initial pH of 6.1, temperature of 29.7°C, and 5.4% inoculum size. This increased $\beta$ -glucosidase activity to 19.1 U/mL.
Fermentation Performance: Bioaugmentation with MZ-4 accelerated the fermentation process by approximately 12 hours compared to the natural process. It resulted in a 47.46% increase in indigo yield and a 58.19% increase in indirubin yield.
Microbiome Remodeling: 16S rRNA sequencing revealed that MZ-4 inoculation intensified early environmental selection, rapidly reducing microbial diversity. The community shifted from a fluctuating, multi-taxon state (dominated by Proteobacteria and Bacteroidetes in natural fermentation) to a stable, lactic acid bacteria-dominated state (Pediococcus and Lactococcus). This shift correlated with accelerated decreases in pH, dissolved oxygen, and oxidation-reduction potential (ORP).
Genomic Insights: Whole-genome sequencing of MZ-4 revealed a 3.13 Mb genome with 44.75% GC content. Functional annotation identified 406 carbohydrate-active enzymes (CAZy), including 121 glycoside hydrolases (GHs). Notably, genes from the GH1 family were prominently represented, providing a genomic basis for the observed $\beta$ -glucosidase activity and indican hydrolysis.

Significance and Claims
The paper claims that the autochthonous bioaugmentation strategy using P. pentosaceus MZ-4 offers a controllable and scalable solution to the inefficiencies of traditional Indigo Naturalis production. By introducing a key indigenous functional strain, the study demonstrates that it is possible to:

Accelerate Conversion: Significantly shorten the fermentation cycle and accelerate the hydrolysis of indican.
Enhance Yield: Substantially increase the accumulation of bioactive indigo and indirubin.
Direct Succession: Remodel the fermentation microbiome from a disordered, fluctuating community to a stable, functional consortium dominated by lactic acid bacteria.
Provide a Mechanistic Basis: Link specific genomic features (GH1 family genes) and enzymatic activities to the observed improvements in product yield and process stability.

The authors conclude that this approach provides a microbiome-directed strategy for modernizing traditional fermentation, offering a pathway for the sustainable bioprocessing and valorization of indigo-yielding plant resources without relying on exogenous enzymes or chemical additives.

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