The use of enzymes within the textile industry has emerged during the last decade and is an environmentally friendly option to the chemical methods commonly used. By cultivating recombinant Escherichia coli expressing several genes, a composition of enzymes that degrade Spandex fibres can be obtained under cost-effective, environmentally friendly conditions. If the Spandex fibres can be degraded without compromising the quality of the cotton fibres, the latter can be recycled into new textiles. This could substantially decrease the amount of incinerated textile waste, lowering the strain on the environment and preserving the energy and water amounts invested in the production of the cotton fibres.
Process Development
During the project we are assembling different constructs to evaluate the optimized way of expressing our proteins. The nine different enzymes can either be assembled into two vectors and transformed into one bacteria, or transformed into one bacteria each, or each enzyme could be expressed separately in nine different bacterial cultures. Once these assemblies are achieved, measurements of expression and activity of the enzymes were initiated. In parallel with these laboratory evaluations, computational simulations are conducted for additional input on how to optimize the process. The results from the lab will be integrated with the computational simulations in an iterative way until optimal conditions for the degradation are achieved.
To produce the nine enzymes in a larger scale, a few factors related to the genetic constructs will be taken into consideration and be further researched in order to maximize the process. One of those is the metabolic burden inflicted by our expression. This concept explains the decrease in growth rate of recombinant bacteria as a result of the decreased amount of resources available for cell growth when recombinant proteins are being expressed at high levels. It is of high interest to monitor this effect closely to be able to adjust parameters like the substrate inflow and recombinant protein expression. A possible control system for this could be to introduce a GFP gene in the chromosomal DNA of the bacteria, which then can act as an integrated marker protein for the expression levels of indigenous genes needed for the cell's capacity to grow. Another consideration is the promoter used. As of now, it is constitutive and the expression is turned on at all times. For a fed-batch cultivation the promoter should be inducible, in order for the bacteria to grow to a certain optical density before initiating recombinant protein expression. The T7-Lac system induced by IDPT seems to be the most established system when producing recombinant proteins in E. coli.
Furthermore, each enzyme expressed have an intrinsic localization tag sending it to the location where it fulfils its purpose in the original host organism. This location can be either intracellular or extracellular and is not known for many of the enzymes expressed. From several perspectives it would be advantageous to have all enzymes transported out of the cell, something that could be achieved by the introduction of a strong secretion tag compatible with the host bacteria used. For example, it is known that the metabolic burden increases when proteins accumulate intracellularly. Furthermore, in most industrial processes cultivating E. coli, a fed-batch system is used. Batch and fed-batch modes are the only options if proteins are present intracellularly since this requires lysis of cells for protein extraction. However, if the constructs could be modified into extracellular transport of the enzymes, it might be possible to run in continuous cultivation mode (chemostat). It is however challenging to achieve extracellular localization of recombinant proteins in bacteria, since the secretion pathway has to be modified. There is a system called ESETEC (from the WACKER company) that might can be used for this purpose [1]. Still, it seems like more research is needed for this to be practicable in a chemostat cultivation.
Service line
Recombinant bacteria expressing the degradation enzymes can be cultivated under controlled conditions in a bioreactor with cheap substrates of low environmental impact. The products from this cultivation system would be biomass, the enzymes used for Spandex degradation, water and carbon dioxide. The enzymes are then isolated and soluted in a buffer optimized for maximum Spandex degradation. Temperature, pH and shaking will also be adjusted for high enzymatic activity.
Textiles will be pre-treated to remove any finishing reagents that might limit the access of the enzymes to the fibres. The fabric will also be cut into pieces of suitable size for the process. Once prepared, the textiles will be placed in the enzyme solution for the calculated amount of time needed. The purified cotton fabric is retrieved and the fibres separated and sent for re-spinning into new textiles. Waste from the enzyme degradation container includes buffer, enzymes and any by-products/trace elements of the degraded Spandex. Waste from the cultivation for enzyme production includes biomass of a non-hazardous strain of E. coli, water and carbon dioxide.
Market research
The market for this business can be viewed from two perspectives; the minimization of waste, and the recycling of cotton fibres. Both are of high interest for the municipalities, but the recycled cotton can also be of interest for clothing companies branding themselves as sustainable.
Minimization of textile waste
In the Swedish national waste prevention program 2014-2017, Naturvårdsverket (The Swedish Environmental Protection Agency) defines textiles as one of four focus areas for future waste handling development. They demand for separate textile waste collection at recycling sites and collection systems for households. However, while a portion of the clothes collected today are re-used mediated by second hand businesses (3.8 kg per person), the majority of textiles are still neither reused or recycled (7.5 kg per person) [2]. This large amount of waste, the increasing awareness of its environmental impact and the Swedish government’s investment in textile waste collection form an extensive market for actors in textile recycling.Recycling and resale of cotton fibres
There is also an increasing awareness among citizens to buy environmentally friendly clothes, promoting the resale of our purified cotton fibres to clothing companies profiled as sustainable. The market for private costumers like these will need to be further researched. Pure cotton textiles are already recycled mechanically in Sweden, and assuming that our purified cotton fibres meet the quality requirements, this is a possible municipal costumer.- [1] J. Kopp, C. Slouka, O. Spadiut, and C. Herwig, “The Rocky Road From Fed-Batch to Continuous Processing With E. coli,” Frontiers in Bioengineering and Biotechnology, vol. 7. Frontiers Media S.A., p. 328, Nov. 20, 2019, doi: 10.3389/fbioe.2019.00328.
- [2] Å. Östlund et al., “Textilåtervinning Tekniska möjligheter och utmaningar ISBN 978-91-620-6685-7.” Accessed: Oct. 07, 2020. [Online]. Available: www.naturvardsverket.se/publikationer.
