Exploiting the polysaccharide breakdown capacity of the human gut microbiome to develop environmentally sustainable dishwashing solutions

Food stains on dishes are complex mixtures of fat, protein and carbohydrates. Many of the carbohydrates in such stains are plant polysaccharides and removal of these stains often requires high temperature and significant levels of chemical detergents. A potential solution to reducing the energy and detergent requirements for effective stain removal during dishwashing is to use specific carbohydrate-active enzymes (CAZymes) to break these polysaccharides down into more soluble oligosaccharides that can be removed from dishes more easily. One route to discovery of CAZymes with the potential to be useful in dishwashing formulations is to exploit the huge untapped resource of novel plant polysaccharide degrading CAZymes encoded by our gut microbiota.
The major nutrient source for the our gut microbiota are polysaccharides from the diet (often called dietary fibre) as these molecules are not broken down by host digestive enzymes. Because of this evolutionary pressure, the number of CAZymes encoded by the gut microbiota to degrade polysaccharides is vast. In this project we aim to exploit the enormous capacity of the gut microbiota to efficiently degrade a wide range of plant polysaccharides to discover novel CAZymes for use in development of more environmentally sustainable dishwashing formulations.

Approach:
Bacteroides spp are one of the main genera present in the microbiota and are known to be particularly adept at polysaccharide degradation, with many species encoding hundreds of CAZymes to enable them to fully deconstruct a wide range of different polysaccharides.

Our approach for enzyme discovery will be to initially screen our in-house human gut Bacteroides library for growth on a range of soluble polysaccharides associated with different problem food stains (e.g., xylans, mannans, glucans; these will be chosen based on P&G priorities). Proteomics will then be used to identify the specific degradative apparatus involved in species that grow well on target polysaccharides, including the exciting possibility of potentially novel CAZyme families identified by distant homology detection and structural modelling using AlphaFold. Initially we will target likely surface endo-acting enzymes as these are the key enzymes involved in the initial rapid breakdown of extracellular target polysaccharides into oligosaccharides. The rapid transit time of the human gut means that CAZymes from the human microbiome have evolved to break these plant polysaccharides down very efficiently. This high activity, coupled to the fact these enzymes are often located in the extracellular milieu and so highly stable and robust in a range of physical conditions, maximises their potential use in dishwashing formulations.

Recombinant versions of target enzymes will be characterised using a range of biochemical techniques available in the host lab to determine the activity and specificity of the purified CAZymes and their role in polysaccharide breakdown.

CAZymes active against the targets will be tested with model soils provided by P&G. Initially, we will employ miniaturised systems to evaluate potentially useful enzymes and promising candidates will then be scaled up at P&G to full dishwashing cycles to understand the role of mechanical agitation, T-ramps and kinetics on the overall performance.

Over the course of the project, novel and interesting enzyme targets will be advanced into structural studies to define the molecular basis for substrate specificity.

Overall, the data generated in this project will provide significant insight into the mechanism of polysaccharide degradation by prominent members of the gut microbiota and underpin the development of novel enzyme strategies to increase the sustainability of novel dishwashing products.