Promoting circularity in the textile industry via yeast metabolic engineering and microbial bioprocesses

The cotton textile industry is currently based on a linear business model featured by depletion of natural resources and generation of an excessive amount of waste of which, globally, less that 1 % is recycled into new garments, often resulting in downcycling. To promote a circular business model, where the waste can be upcycled within the industrial textile production process, we explored the possibility to valorise the waste streams of an apparel textile manufacturing company. We show the use and valorisations of two waste streams, that are the post-industrial cotton patches and the NaOH-rich waste stream from the mercerisation process of cotton fabrics. In particular, the NaOH-rich waste was used for the pretreatment of mechanically shredded cotton before enzymatic hydrolysis; the combination of the mechanical, chemical, and enzymatic treatment resulted in a recovery rate of cotton into glucose of about 90 % [1]. The cotton derived glucose was used to produce L-lactic acid via a Saccharomyces cerevisiae strain engineered to replace alcoholic fermentation with lactic fermentation and subsequently evolved and selected for production od L-lactic acid at pH below 3.0 [2]. Overall, the process resulted in the conversion of 82.7 % of glucose into L-lactic acid, that besides being an established platform chemical, it can substitute acetic acid traditionally used in the textile dyeing process. An additional up-cycling route of the cotton waste has been explored engineering the yeast Kluyveromyces marxianus to produce dyeing molecules belonging to the violacein family. A chassis strain for production of aromatic products [3] was engineered to maximise the synthesis of tryptophan and hence to express heterologous genes specific for the biosynthesis of violacein species from tryptophan. As a proof of concept, glucose derived from cotton pretreatment and hydrolysis was used in a fermentation process with engineered K. marxianus, thus producing a violacein molecule that has successfully been used in the industrial dyeing process of cotton and wool yarns. This study validates the utilization of cotton post–industrial waste as a possible feedstock for the production of commodity chemicals in microbial cell-based biorefineries. The presented strategy demonstrates the possibility of implementing a circular bioeconomy approach in manufacturing textile industries. [1] Simonetti et al. Microbial Cell Factories (2024) 23:106. doi:10.1186/s12934-024-02384-3 [2] Liu CL, Lievense JC 2005. Lactic acid producing yeast. WO2005052174A2, 2005. [3] Rajkumar, A. S. and Morrissey, J. P. Microbial Cell Factories (2020) 19, 207. doi:10.1186/s12934-020-01461-7