With pressing environmental issues such as rising temperatures, climate change, deforestation, and pollution, affecting the Earth, many industries are taking new initiatives to reduce their footprint on the world; by changing their materials and manufacturing processes, to reduce environmental degradation.

One such example is Armstrong. Armstrong is a global construction manufacturer; they mass produce ceiling tiles, and floorboards.

Recently, as part of an initiative to be more sustainable and environmentally conscientious, Armstrong switched from using raw trees to produce their ceiling tiles, to recycling paper products. This change would be enable usage of already available resources, repurposing old paper to create something new, rather than cutting down new trees to produce their ceiling tiles.

But this well-intentioned change has unforeseen consequences.

Production of paper-based ceiling tiles is a “wet” process. A million gallon water system is run through the system to produce the tiles, then treated and reused.

The switch to paper products, which have already been processed once, causes short chain cellulose fibers that were not incorporated into the tiles to be carried away in the water system. A variety of microbes feed off these cellulose fibers in the water system. Some bacteria strains produce butyric acid as a byproduct of anaerobic fermentation. Butyric acid has a highly unpleasant smell; it is the major distinctive smell in human vomit, and can be detected by humans at concentrations as low as 10 parts per million.

Butyric acid production is activated by low oxygen conditions. Regulating the oxygen levels of such a large system, a million gallons, is challenging. Armstrong uses aeration pumps and basins, but these can get clogged, preventing them from functioning correctly at times. The water system can change from its targeted oxygen level of 2.0 mg/L, to nearly 0 mg/L oxygen, resulting in anaerobic conditions. When this occurs, it activates an anaerobic fermentation pathway, in which butyric acid is an end product.

Currently Armstrong remediates this issue by periodically using biocides when the butyric acid concentration is too high, chemicals that eliminate all microbial growth in the water system. This solution has many drawbacks. First, it is a short term solution, it kills all the microbial growth, but the butyric-acid-producing bacteria re-emerge, except now some may even be resistant to the biocides. Biocide treatment is an expensive treatment and also has to be closely monitored. Lastly, there are potential environmental risks and hazards; the biocides could leave the closed factory system and contaminate the natural ecosystem, negatively affecting wildlife and their habitats.

Faced with a dilemma, Armstrong presented us with this real world industrial problem with environmental consequences, asking us if we could use the power of synthetic biology to create a cost effective, scalable, environmentally safe, long term, and sustainable solution that could be applied immediately in their factory.

Our Solution

Armstrong’s ceiling tile factory problem with butyric acid could be approached from many different angles. The butyric acid itself could be broken down into innocuous substances, the butyric acid pathway could be prevented or averted by inhibiting the enzyme β-hydroxybutyryl-CoA dehydrogenase, the starch molecules that provided food for the microbes could be eliminated.

As we were doing applied research, with a real world application and industrial issue that was affecting millions, we took into account cost effectiveness, scalability, sustainability, and environmental effects.

Ultimately we chose to genetically engineer a Saccharomyces cerevisiae yeast cell to produce and secrete a highly effective form of the starch degrading enzyme amylase. The amylase would break the bonds in the starch molecules, and the resultant sugars would be metabolized by the yeast cell.

By removing the starch molecules from the water system, we would be effectively eliminating the food and energy source for the problematic, butyric-acid producing bacteria.

Why S.cerevisae?

The butyric acid levels become problematic when the system goes anaerobic, as it triggers the butyric acid pathway. Our organism would have to be able to survive and thrive in both anaerobic and aerobic conditions, thus yeast provided the perfect organism.

Why amylase?

Alpha amylase is a form of the enzyme that has the capability to hydrolyse the α bonds connecting the monosaccharides in the starch molecules. Unlike beta amylase, which breaks bonds at the ends of starch molecules, alpha amylase can breaks bonds on both the ends and middle of the starch molecule. This increases the effectiveness of the enzyme. We used an alpha amylase gene from Bacillus amyloliquefaciens, a type of bacteria that naturally produces and secretes alpha amylase. Alpha amylase can also act on any substrate, making it versatile and suited for the large scale conditions of the industrial water system.

This approach is unique, previously the only industrial uses of amylase were for production of high fructose corn syrup and ethanol production from grains. This is the first time an amylase has been applied as a solution in a large-scale industrial construction manufacturing water system.