Exploring Hidden Origins of Lac Pigment: A Breakthrough In Microbial Symbiosis

Bengaluru: India has been a key global producer of the red pigment laccaic acid for millennia, using it in textiles, food colouring, handicrafts and traditional art. Long believed to be produced by the lac insect, a new research from the Indian Institute of Science (IISc) reveals that the pigment is actually produced by a yeast-like fungus living inside the insect.

Ancient craft, modern discovery:

The lac insect, found across India and commercially cultivated by tribals in states like Jharkhand, Chhattisgarh and Bihar, feeds on tree sap and secretes resin (shellac) and produces the red pigment. For thousands of years, India has been a key producer of lac pigment. As a source of pigment, the lac insect is very popular. But the molecular basis of this pigment synthesis wasn’t clear. And through the study, the scientists have explored this unknown discovery.

Breakthrough Study:

Scientists led by assistant professor Shantanu Shukla from IISc’s Department of Developmental Biology and Genetics (DBG) and corresponding author of the study published in the “Proceedings of the National Academy of Sciences” found that the insect lacks the genes required to synthesise the pigment. Instead, the complete gene set responsible for pigment production was found in a fungal symbiont inside the insect.

Real Pigment Producer:

The lac insect lives on trees like the Flame of the Forest, feeds on sugary sap and produces a sticky substance called shellac along with the red pigment. But until now, scientists didn’t know how the pigment was actually made.

Interview Insight: Fungal Genetics Over Insect Capacity:

“This yeast-like fungus, not the insect or its associated bacterium Wolbachia, carries the genes for laccaic acid synthesis,” Prof. Shukla, in an exclusive interview, told ETV Bharat. One key ingredient, tyrosine—an amino acid crucial to the pigment’s biochemical pathway—is absent in the insect and is minimally present in the tree sap, further confirming the insect’s dependency on the fungus. Such missing ingredients are usually supplied by symbiotic bacteria or fungi that live inside insect bodies and secrete these molecules in exchange for housing. The fungus provides it, along with other chemicals needed for pigment production.

PhD student Vaishally noted the difficulty in accessing the fungus, which cannot be grown outside the insect body. “All experiments had to be done using host plant-reared insects,” she said. Spraying fungicide on the insect reduced pigment production and stunted its growth, underlining the fungus’s role in providing both pigment and essential nutrients.

“The fungus is not just responsible for colour, but also contributes vital amino acids and vitamins that the insect cannot obtain from its sap-based diet,” Prof. Shukla explained. The fungus has co-evolved with the insect over millions of years as a nutritional symbiont. He emphasised that it was a team effort and the study took three years from initial idea to full execution and publication.

Motivation & Curiosity Sparked the Study:

During the interview, while discussing the motivation and process behind the study, Prof. Shukla said, “I am fascinated by microbial symbiosis—especially the intricate relationships between insects and microbes. Every organism harbors a unique microbiome, but in insects, it’s particularly compelling. Beyond the gut microbiome, there exist specialised symbionts that reside in organs like the fat body, having co-evolved over millions of years to provide critical benefits to their insect hosts.”

The Lac Insect as a Research Model:

Prof. Shukla’s lab focuses on the study of insect-microbe interactions. He recalled how the lac insect initially caught his attention due to its economic and cultural significance, as well as its peculiar biology. He said, “We were curious about how the insect produces its signature red pigment. Our early interest was in understanding the insect’s microbial symbiosis and how it supports the insect’s health, development, and reproduction. That led us to wonder whether microbes could also play a role in pigment production.”

Mapping the Pigment’s Biochemical Origins:

This curiosity led to a major discovery. The team confirmed the presence of a yeast-like fungus inside the lac insect. Prof. Shukla explained, “The structure of the lac pigment, known as a polyketide, is complex—with carbon rings and amino acids. It seemed unlikely that the insect could independently synthesise such a compound. We hypothesised that the pigment might either be acquired through diet or via microbial partners.”

Ruling out the diet:

To test this, the team investigated the insect’s food source—the plant sap—but found that the sap did not contain the pigment or its precursors. This eliminated diet as a possible source. Attention then turned to the insect’s microbiome. The team sequenced the full bacterial and fungal microbiome of the lac insect, identifying two key candidates: a bacterium from the Wolbachia genus and a yeast-like fungus.

While earlier studies had noted the presence of a fungus in the insect, none had sequenced or identified it. In this study, the researchers found that neither the insect nor the bacterium possessed the genes needed to synthesise tyrosine or other precursors of the pigment. The yeast-like fungus, however, had the full set of genes required for laccaic acid production—the primary component of the red pigment.

“This was our first strong evidence that the pigment was of fungal origin. We mapped the tyrosine synthesis pathway and discovered that every step was present only in the fungal genome. Further, we quantified tyrosine metabolites in the insect and confirmed their presence, supporting the metabolic activity of the fungus," said Prof. Shukla.

Inside the Insect: A Hidden Symbiont:

What made the finding even more remarkable was that the fungus doesn’t reside in the insect’s gut. Instead, it’s an intracellular symbiont—living inside the insect’s cells, including its eggs, which means it is passed from mother to offspring through vertical transmission. “It’s quite fascinating,” he said. The fungus is relatively large, yet it has evolved to live within the host and be inherited across generations.

Genome Sequencing Confirms the Origin:

To confirm their findings, the researchers sequenced the genomes of the insect and its bacterial symbiont, specifically searching for genes related to pigment biosynthesis. Prof. Shukla emphasised, “None were found in either. But the fungal genome had them all, including the gene cluster responsible for tyrosine production.”

Implications, Challenges and Industrial Potential:

When asked about the implications of the discovery, he said, “We now know the exact gene cluster responsible for pigment synthesis. This opens the door to potentially replicating pigment production using this fungus outside the insect. However, one major challenge remains: the fungus cannot be cultured independently in the lab. It has co-evolved with the insect over millions of years and survives only within it.”

Despite this, Prof. Shukla remains optimistic and said, "Understanding the biochemical pathway and genes involved gives us a powerful tool for future research and possibly industrial pigment production. The findings not only unravel the mystery of pigment origin but also highlight the broader significance of microbial symbiosis in insect biology.”

Reflecting on the technical challenges, he noted that the lac insect is covered in a hard resin, making access and dissection extremely difficult. “Extracting DNA from an uncultivable fungus was particularly challenging. Since nothing was previously known about the genomes involved, we had to develop new protocols from scratch—whether for sequencing, metabolite quantification, or studying the fungal symbiont.”

Prof. Shukla concluded by noting that similar fungal symbionts might exist in other economically important insects. “We’re now exploring how such symbioses originated—how the fungus entered this relationship and adapted genetically to the insect host. Before this co-evolution, the fungus likely lived freely in the environment. Today, it serves not only in pigment synthesis but also helps compensate for the nutrient-deficient sap diet of the insect by providing essential amino acids and vitamins.”

The Power of Microbial Symbiosis:

“This study underscores how much there is still to learn about the microbial world within insects,” he said, “and how critical fungi may be to the evolution and survival of their hosts.”