Background
Every day, with every breath, a large number of molecules enter our bodies. The quality of air directly affects our health, even our lives. However, harmful gases are very common in our lives. For example, nicotine, tar, and formaldehyde, commonly found in second-hand smoke, are classified as Group 1 carcinogens. The presence of odorous gases in places such as garbage not only affect the mood of the residents, but also lead directly to diseases such as headaches, respiratory problems, eye, nose and throat symptoms[1].
We have investigated the harmful components of the atmosphere, we focused on seven harmful substances:
- Nicotine: Nicotine, a prevalent constituent of second-hand smoke, acts as an addictive agent on acetylcholine receptors and may elevate cancer risk[2]. To safeguard the health of non-smokers, integrating the function of nicotine-degradation in to E.coli for air purification is crucial.
- Benzo[a]pyrene: Tar in smoke, rich in carcinogenic polycyclic aromatic hydrocarbons (PAHs) like benzo[a]pyrene, poses a significant threat to human health, being a key factor in various cancers.
- Formaldehyde: Formaldehyde, stemming from incomplete tobacco combustion, is inhalable and can directly contact the skin. In the carcinogen list published by the International Agency for Research on Cancer (IARC) of the World Health Organization, formaldehyde is categorized as a Group 1 carcinogen[3].
- Indole: Indole is a product of anaerobic fermentation of food remnants in the gastrointestinal tract and represents the terminal metabolite in tryptophan degradation. Among the olfactory compounds frequently encountered in animal husbandry, indole has an olfactory threshold of < 0.0001 ppm, rendering it notably recognized as one of the most pungent and repugnant odors in human perception[4].
- Butyric acid, which often emanates from bathrooms and produces intolerable odors, comprises a substantial portion of up to 13 mg/g[5], making it a principal malodorous compound. The unpleasant odor of butyric acid not only impacts individuals' mood but also their health. Conventional air purification methods merely absorb foul-smelling gases without degradation. In contrast, our engineered E.coli can both degrade butyric acid and simultaneously produce acetyl butyrate, imparting a fruity aroma, presenting a dual solution for odor elimination and pleasant fragrance, ultimately enhancing air quality.
- Hydrogen sulfide: Hydrogen sulfide is a widely present hazardous substance in daily life, primarily characterized by its flammability and toxicity. The toxicity of hydrogen sulfide is significant, acting as a potent neurotoxin and causing strong irritation to mucous membranes. Even at low concentrations, hydrogen sulfide has a powerful and unpleasant odor, often described as a rotten egg smell, and people can detect this odor at concentrations as low as 0.00041 ppm[6,7].
- Ammonia: Ammonia is an irritating gas with a strong odor, mainly originating from human excrement, pet urine, rotting food, and similar sources. Besides causing discomfort due to its unpleasant smell, ammonia can also pose health risks to humans. Simultaneously, ammonia is a preferred nitrogen source for E.coli, and it can be converted to nitrate through a series of processes.
What did we do?
In order to eliminate these harmful substances, we designed relative metabolic pathways to achieve degradation of harmful substances in E.coli .
We also optimised some of the metabolic pathways including the combination of the butyric acid degradation pathway and the butanol esterification pathway, to attain a "deodorization + fragrance production" effect. To eliminate E.coli 's inherent odor, we knocked out tnaA using λ-Red homologous recombination system, ensuring that E.coli does not produce its own odorous substance, indole. In the formaldehyde degradation pathway, we knock out frmA to shift formaldehyde towards assimilation rather than dissimilation, reducing CO2 production and converting it to a metabolizable substance.
To find the most beneficial mutations for improved efficiency, we decided to use virtual screening methods from a large pool of candidates. Thus, we developed a multi-step virtual screening model based on molecular docking and molecular dynamics simulation. Using this approach, we optimized the enzymes involved in the project.
To ensure our project can be effectively applied in everyday life, we have created compatible hardware designed to remove harmful substances from the air using our biotechnology. In this hardware, harmful gases will be enriched, and our immobilized E.coli will be used to purify these substances. Additionally, we have incorporated UV sterilization to ensure biosafety.
