Part:BBa_K4719013
AGM1-NAG5-UAP1 operon for incorporation of N-acetylglucosamine into bacterial cellulose
Sequence and Features
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Introduction
Vilnius-Lithuania iGEM 2023 team's goal was to create a universal synthetic biology system for Komagataeibacter xylinus for in vivo bacterial cellulose polymer composition modification. Firstly, we chose to produce a cellulose-chitin polymer that would later be deacetylated, creating bacterial cellulose-chitosan. This polymer is an easily modifiable platform when compared to bacterial cellulose. The enhanced chemical reactivity of the bacterial cellulose-chitosan polymer allows for specific functionalizations in the biomedicine field, such as scaffold design. As a second approach, we designed indigo-dyed cellulose that could be used as a green chemistry way to apply cellulose in the textile industry. Lastly, we have achieved a composite of bacterial cellulose and polyhydroxybutyrate (PHB), which is synthesized by K. xylinus.
Bacterial cellulose-chitin polymer was achieved by increasing the production of UDP-N-acetylglucosamine, which can be recognized as a viable substrate for cellulose synthase and incorporated in the bacterial cellulose polymer. We employed two strategies to produce this material. The first approach was to add N-acetylglucosamine into the growth medium BBa_K4719013, and the second one was the production of N-acetylglucosamine by K. xylinus from simple sugars such as glucose, fructose, and saccharose in the growth medium BBa_K4719014.
Usage and Biology
This construct produces an excess of UDP-N-Acetylglucosamine (GlcNAc) in K. xylinus, which can be used by cellulose synthase to produce bacterial cellulose-chitin polymer. Incorporation of N-acetylglucosamine has been previously demonstrated by M. H. Tan (2019) and V. Yadav (2010). K. xylinus requires genetic modification in order to incorporate GlcNAc into the bacterial cellulose as the natural conversion to UDP-GlcNAc is not efficient. The genes in this composite code for proteins that are responsible for the uptake of extracellular GlcNAc and conversion to UDP-GlcNAc. Therefore, the growth medium has to be supplemented with GlcNAc.
Bacterial cellulose-chitin copolymer has applications in the biomedicine field due to in vivo biodegradability by the lysosome. However, this copolymer is an intermediate step in your biological system since we chose to improve the qualities of the material by deacetylation. This second enzymatic step produces a bacterial cellulose-chitosan copolymer that has the added benefits of antibacterial activity and amino groups for easier functionalization.
Since polymer production occurs in K. xylinus it requires a specific plasmid (pSEVA331-Bb) backbone for successful replication. We choose to use BBa_K1321313 as it was characterized by iGEM14_Imperial team as the most suitable synthetic biology tool for Komagateibacter species. We performed PCR of the plasmid eliminating mRFP in order to preserve Anderson promoter J23104 BBa_J23104, RBS BBa_B0034 and terminator BBa_B0015. AGM1, NAG5 and UAP1 were assembled into the backbone by Gibson assembly.
Experimental characterisation
Polymer production
Bacterial cellulose-chitin polymer is synthesized by K. xylinus grown in the glucose yeast extract broth (GYB) while shaking at 180 rpm at 28°C, for 7 days. Varying concentrations of glucose and N-acetylglucosamine have been added to determine the best combination of growing conditions. We determined the optimal carbon source ratio of 1% glucose and 1% N-acetylglucosamine.
Floresence analysis of N-acetylglucosamine incorporation
To determine if the polymer contains N-acetylglucosamine residues, we used fluorescence lectin staining with wheat germ agglutinin (WGA), Alexa Fluor™ 680 conjugate selectively binding to N-acetylglucosamine. Therefore, natural cellulose should not give a visible signal at this wavelength. Construct for incorporation of N-Acetylglucosamine into bacterial cellulose improved fluorescence signal substantially, showing consistent distribution of the target monomers.
Chracterization of polymer surface with SEM
For further verification of bacterial cellulose-chitin polymer structural differences from natural bacterial cellulose, we performed scanning electron microscopy (SEM).
References
1.Teh, M.Y. et al. (2019) ‘An expanded synthetic biology toolkit for gene expression control in acetobacteraceae’, ACS Synthetic Biology, 8(4), pp. 708–723. doi:10.1021/acssynbio.8b00168.2.Yadav, V. et al. (2010) ‘Novel in vivo degradable cellulose-chitin copolymer from metabolically engineered gluconacetobacter xylinus’, Applied and Environmental Microbiology, 76(18), pp. 6257–6265. doi:10.1128/aem.00698-10.
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