Pune scientists develop eco-friendly bacterial route to produce industrial pigment

Hindustan Times

4 days ago

Offering a green alternative to traditional chemical methods, scientists at the Agharkar Research Institute have pioneered a sustainable microbial route to produce cerium sulfide (Ce₂S₃), a vibrant rare earth pigment with wide industrial use - industrial coatings, ceramics, and energy efficient construction materials. This is the first recombinant microbial method for producing cerium sulfide using genetically-engineered bacteria under low-temperature, non-toxic and scalable conditions. (SOURCED)
This is the first recombinant microbial method for producing cerium sulfide using genetically-engineered bacteria under low-temperature, non-toxic and scalable conditions. Traditionally, cerium sulfide production has required energy intensive chemical processes, involving temperatures as high as 1700°C and hazardous sulfur-based chemicals like hydrogen sulfide (H₂S) or carbon disulfide (CS₂). These methods are not only expensive but also environmentally and occupationally dangerous.
Addressing this challenge, a research team led by microbiologist Prashant Dhakephalkar, with key contributions from Dr P P Kanekar, and researchers Sonal Shete and Neelam Kapse, developed an innovative microbial route by genetically modifying Escherichia coli (E. coli) to carry out the sulfate to sulfide conversion required for pigment formation.
The team began with the isolation of a novel sulfate reducing bacterium, Pseudodesulfovibrio sp. MCM B-508, from oilfield wastewater. This native strain could convert cerium sulfate into cerium sulfide, but showed low efficiency due to its anaerobic growth requirements and slow cell proliferation.
To overcome these limitations, researchers cloned the key dsrAB genes responsible for producing the enzyme, dissimilatory sulfite reductase (dSiR), into E. coli, a fast-growing, easily manipulated lab bacterium. To improve protein folding and solubility, the recombinant E. coli was also co-expressed with a molecular chaperone system (pGro7).
The result was A 71.23% sulfate conversion efficiency, achieved under aerobic and low-temperature (55°C) conditions - a significant leap in microbial pigment production.
X-ray diffraction (XRD) analysis confirmed that the pigment produced was predominantly in the gamma-phase of Ce₂S₃, the most desired form, for its intense red colour, heat stability, and non-toxic nature. This form is particularly suitable for automotive paints, powder coatings, and smart ceramics, where durability and non-toxicity are critical.
The engineered E. coli could tolerate cerium sulfate concentrations up to 300 ppm and yielded 0.71 grams of pigment per gram of precursor, demonstrating both resilience and industrial feasibility.
'This is a major step towards replacing toxic, energy intensive processes with sustainable biomanufacturing. It aligns with global green chemistry goals and offers a viable alternative for industries looking to reduce their environmental footprint. This is the first time anyone has demonstrated microbial synthesis of cerium sulfide, using a recombinant system. The process replaces toxic chemicals with a clean, bio-based solution,' said Neelam Kapse.
'The implications are vast. This method could revolutionise the pigment industry and lead to greener alternatives in applications ranging from automotive paints to energy-efficient building coatings,'added Dhakephalkar.
Unlike traditional sulfate-reducing bacteria that require strict anaerobic conditions and are difficult to scale, the recombinant E. coli system thrives under aerobic conditions and can be easily controlled in bioreactors.
With the rising global demand for rare-earth materials and non-toxic pigments, this breakthrough places India at the forefront of synthetic biology and clean-tech innovation. The researchers are now focused on scaling the process and exploring industrial collaborations to bring this green technology to the market.