Project

Designer Suzanne Lee showed that bacterial cellulose could be used in novel ways, including to make clothing using a more eco-friendly process. Our team set out to demonstrate that new characteristics could be added to the cellulose produced by Acetobacter xylinum using synthetic biology methods. Altering physical characteristics such as strength, color, odor, etc. would result in exciting new materials to create with.

Cellulose is a polymer made up of long β-1,4 glucan chains. In Acetobacter, the enzyme cellulose synthase catalyzes the biosynthesis of cellulose from UDP-glucose. We hypothesized that mixed polymers containing different sugars would have unique physical properties. Cellulose synthase has been reported to utilize UDP-N-acetylglucosamine (NAG) molecules (components of chitin) as well, resulting in a polymer containing both glucose and NAG units- a cellulose-chitin hybrid. We wanted to test the properties of this new material, so we set out to engineer Acetobacter to produce this hybrid polymer.

Strategy

The yeast Candida albicans produces chitin and uses it in spore formation. To incorporate NAG into Acetobacter cellulose, we focused on three yeast genes (the pathway consisting of NAG5 (GlcNac kinase) catalyzes the conversion to GlcNac-6P, AGM1 (Phosphoacetyl-glucosamine mutase) which converts GlcNac-6-P to GlcNac-1-P, and UAP1 (UDP-GlcNac pyrophosphorylase) which adds UDP.

The most efficient method was to use Gibson assembly to piece together each gene from small, ovelapping fragments of between 300 and 500bp ("G-blocks") and clone it into pSB1C3 separately. We could not construct the entire pathway with G-blocks because it was too large, and there is a limit of six fragments for efficient Gibson assembly. The coding sequences were modified to reflect codon usage in Acetobacter, and an Acetobacter RBS was added in front of each gene. The G-blocks that we had synthesized for each gene are shown below:

• G-blocks for AGM1
  

  GAATTTCAGATAAAAAAAATCCTTAGCTTTCGCTAAGGATGATTTCTGGAATTCGCGGCCGCTTCTAGAGTGAGGAGGATGAACGACGCATGTCAATTGAACAAACATTATCACAATATTTACCATCACATCCAAAACCACAAGGTGTGACATTTACTTATGGGACAGCAGGATTCCGTATGAAAGCTGATAAATTAGATTATGTCACTTTTACCGTTGGGATCATTGCTTCATTAAGATCGAAATATTTACAAGGGAAAACCGTTGGTGTTATGATTACTGCTTCTCATAATCCCCCGGAAGATAATGGGGTTAAAGTTGTTGATCCATTAGGTAGTATGTTGGAAAGTTCATGGGAAAAATATGCTACTGATTTAGCCAATGCTTCTCCTTCTCCTTCTA 402

  TATGCTACTGATTTAGCCAATGCTTCTCCTTCTCCTTCTAACGATTCAGAAGGGGAAAAAAATCTGTTGGTGGAAGTTATTAAAAATTTGGTTTCTGATTTGAAAATTGATTTATCTATTCCTGCTAATGTTGTTATTGCTAGGGATTCAAGAGAATCTAGTCCAGCATTATCAATGGCAACTATTGATGGATTTCAAAGTGTTCCCAACACTAAATATCAAGATTTTGGATTATTTACTACCCCAGAATTACATTATGTTACTAGAACATTAAACGATCCCGATTTTGGTAAACCAACTGAAGATGGTTATTATTCTAAATTAGCAAAATCTTTCCAAGAAATTTATACCATTTGTGAATCTAATAATGAAAAAATCGATATAACTATTGATGCTGCTAATGGTGTTGGAGCCCCCAAA 420

  TATAACTATTGATGCTGCTAATGGTGTTGGAGCCCCCAAAATTCAAGAATTATTAGAAAAATATTTACATAAAGAAATCAGTTTTACCGTGGTTAACGGTGATTATAAACAACCAAATTTATTAAATTTTGATTGTGGAGCTGATTATGTCAAGACTAATCAAAAATTACCTAAAAATGTCAAACCAGTAAATAATAAATTATATGCTTCATTTGATGGCGATGCGGATAGATTAATATGTTATTATCAAAACAATGATAATAAATTCAAATTATTAGATGGTGATAAATTATCGACGTTATTTGCGTTATTTTTACAACAATTATTTAAACAAATTGACCCCACTAAGATTTCATTGAATATTGGTGTGGTTCAAACTGC 381

  CCCACTAAGATTTCATTGAATATTGGTGTGGTTCAAACTGCTTATGCTAATGGATCTTCAACAAAATATGTTGAAGATGTTTTGAAAATTCCTGTTCGTTGTACTCCTACTGGTGTTAAACATTTACATCATGAAGCTGAAAATTTCGATATTGGTGTATATTTTGAAGCTAATGGGCATGGTACAGTTATTTTCAATCCTGAAGCCGAAAAGAAAATTTTCAATTATAAACCAAATAATGATAATGAAGCTAAAGCTATTAAAGTTTTACAAAATTTTAGTCAATTAATTAATCAAACTGTGGGTGATGCAATTTCCGATTTATTGGCCGTGTTAATTGTCGTTCATTATTTGAAATTATCACCAAGTGATTGGGATAATGAATATACTGA 392

  TTGAAATTATCACCAAGTGATTGGGATAATGAATATACTGATTTACCTAATAAATTGGTTAAAGTGATTGTTCCTGATAGATCTATATTCAAAACTACAAATGCTGAAAGAACTTTGGTTGAACCTAAAGGTATGCAAGATGAAATTGATAAATTAGTTGCCCAATATCCAAATGGAAGATCTTTTGTAAGAGCTTCTGGTACTGAAGATGCTGTTAGAGTTTATGCTGAAGCTGATACGCAAAATAACGTTGAAGAATTATCTAAAGCAGTATCTGAATTAGTTAAATAGTACTAGTAGCGGCCGCTGCAGTCCGGCAAAAAAGGGCAAGGTGTCACCACCCTGCCC 348

• G-blocks for NAG5
  

  GAATTTCAGATAAAAAAAATCCTTAGCTTTCGCTAAGGATGATTTCTGGAATTCGCGGCCGCTTCTAGAGTGAGGAGGATGAACGACGCATGAGACAAGCTATATTTTCCAACCCTAACGATGCTGCTGAGTATTTGGCAAACTATATCATTGCCAAAATCAACTCCACCCCCAGAACATTTGTTCTTGGCCTTCCAACCGGGTCATCCCCTGAAGGCATTTATGCCAAATTGATCGAAGCCAACAAGCAAGGGCGGGTTAGTTTCAAAAACGTCGTGACCTTCAACATGGACGAGTATTTGGGATTGGCCCCATCTGAC 320

  CTTCAACATGGACGAGTATTTGGGATTGGCCCCATCTGACTTGCAGTCGTACCATTATTTCATGTACGACAAGTTTTTCAACCATATCGATATCCCGCGTGAAAATATCCACATCTTGAACGGATTGGCCGCAAACATCGACGAGGAGTGTGCCAACTACGAAAAGAAAATCAAACAATACGGAAGAATCGATTTGTTCTTAGGTGGGTTGGGCCCAGAAGGTCATTTGGCATTCAACGAAGCGGGATCATCAAGAAACTCTAAAACAAGAAAGGTCGAGTTGGTCGAAAGTACCATCAAGGCAAACAGCAGGTTTTTCGGG 322

  GGTCGAAAGTACCATCAAGGCAAACAGCAGGTTTTTCGGGAACGACGAGAGCAAGGTCCCTAAATATGCATTGAGTGTTGGTATTTCCACCATCTTGGACAACTCAGACGAAATTGCCATTATCGTGTTGGGCAAAAGTAAACAATTTGCATTGGACAAAACTGTAAACGGGAAACCAAACGACCCAAAATACCCATCAAGCTATTTACAAGACCACGCAAATGTCTTGATTGTTTGCGATAACGCTGCCGCTGGATTAAAGTCAAAGTTGTAGTACTAGTAGCGGCCGCTGCAGTCCGGCAAAAAAGGGCAAGGTGTCACCACC 325

• G-blocks for UAP1
  

  GAATTTCAGATAAAAAAAATCCTTAGCTTTCGCTAAGGATGATTTCTGGAATTCGCGGCCGCTTCTAGAGTGAGGAGGATGAACGACGCATGACAGTTAAATCACAACAACAAATTATTGATTCATTCAAACAAGCTAATCAAGATCAACTTTTCCAATATTATGATTCATTGACAATAAATCAACAACAAGAATTTATAGATCAATTGTCAACTATTGAAGAACCAGCTAAATTGATTTCTACTGTAGAACAAGCGATTCAATTTTCTCAAACCAATTCTACATCAAGAAATTTCACTCAATTACCTAATGAACAAACAGCATCAACTTTAGATTTATCAAAAGACATTTTACAAAATTGGACCGAATTAGGTTTAAAAGCCATTGGTAATGGAGAAGTTGCCGTTTTATTGATGGCAGGAGGTCAAGGAAC 433

  GAGAAGTTGCCGTTTTATTGATGGCAGGAGGTCAAGGAACTAGATTAGGTTCAAGTGCTCCCAAAGGTTGTTTTAATATTGAATTACCATCACAAAAATCATTATTTCAAATTCAAGCTGAAAAAATTTTGAAAATTGAACAATTAGCTCAACAATATTTGAAATCGACTGAAAAACCAATTATTAATTGGTATATTATGACCAGTGGTCCTACTAGAAATGCTACTGAATCATTTTTCATTGAAAATAATTATTTTGGTTTAAATTCTCATCAAGTGATTTTTTTCAATCAAGGAACGTTGCCATGTTTTAATTTACAAGGCAATAAAATCTTATTAGAACTGAAAAATTCAATTTGTCAATCACCCGATGGTAATGGTGGATTATATAAGGC 384

  TTTGTCAATCACCCGATGGTAATGGTGGATTATATAAGGCATTAAAAGATAATGGAATACTAGATGATTTCAATTCTAAGGGCATCAAACATATTCATATGTATTGTGTTGATAATTGTTTAGTTAAAGTTGCTGATCCAATTTTCATTGGATTTGCCATTGCCAAAAAATTTGATTTGGCAACAAAAGTGGTTAGAAAAAGAGACGCTAATGAAAGTGTTGGATTAATTGTTTTAGATCAAGATAATCAAAAACCTTGTGTTATTGAATATAGTGAAATTTCTCAAGAATTGGCTAACAAAAAAGACCCTCAAGATTCTTCTAAATTATTTTTAAGAGCTGCTAATATTGTTAATCATTATTATTCAGTGGAATTTTTAAATAAAATGATTCCTAAATGGATTTCATCTCAAAAATATTTACCATTCC 429

  ATTCCTAAATGATTTCATCTCAAAAATATTTACCATTCCATATAGCTAAAAAGAAAATCCCAAGTTTGAATTTAGAAAATGGAGAATTTTATAAACCAACTGAACCAAATGGTATTAAATTAGAACAATTCATTTTCGATGTTTTCCCATCAGTCGAATTAAATAAATTTGGTTGTTTAGAAGTCGATCGTTTAGATGAATTTTCTCCATTGAAAAACGCCGATGGTGCTAAAAATGATACTCCAACAACTTGTAGAAATCATTACCTTGAAAGAAGTTCCAAATGGGTTATTCAAAATGGTGGAGTTATTGATAATCAAGGATTAGTTGAAGTTGATAGTAAAACCAGTTATGGTGGTGAAGGTTTAGAATTTGTTAATGGTAAACATTTCAAAAATGGCGATATTATTTAATACTAGTAGCGGCCGCTGCAGTCCGGCAAAAAAGGGCAAGGTGTCACCACCCTGCCC 470

This worked very well, and resulted in the submission of three new parts to the BioBrick Library (Bba_K850000, Bba_K850001, Bba_K850002). We then set out to fuse these three genes into a single pSB1C3-based plasmid. PCR primers were synthesized to bracket each of the three genes and also add sequernce that would facilitate Gibson assembly of the entire pathway. Our reasoning was that we could then use Gibson assembly to piece together the three genes in the pathway together into pSB1C3. The sequences of these primers is shown below. We included two forward primers dfor the AGM1 gene- one that included the T7 promoter (known to work in Acetobacter, whose own promoters are not clearly understood yet), and one that did not.

 

Primers

• Forward AGM1 (biobrick plasmid + promoter
  

  CAGATAAAAAAAATCCTTAGCTTTCGCTAAGGATGATTTCTGGAATTCGCGGCCGCTTCTAGAGTAATACGACTCACTATAGGGAATACAAGCTACTTGTTCTTTTTGCATGAGGAGGATGAACGACGCATG

• Reverse AGM1
  

  GCAGTATCTGAATTAGTTAAATAGTGAGGAGGATGAACGACGCATGAGACAAGCTATATTTTCCAACCCTAACGATGCTGCGCAGCATCGTTAGGGTTGGAAAATATAGCTTGTCTCATGCGTCGTTCATCCTCCTCACTATTTAACTAATTCAGATACTGC

• Forward NAG5
  

  CGTTGAAGAATTATCTAAAGCAGTATCTGAATTAGTTAAATAGTGAGGAGGATGAACGACGCATGAGACAAGCTATATTTTCCAACCC

• Reverse NAG5
  

  GCTGGATTAAAGTCAAAGTTGTAGTGAGGAGGATGAACGACGCATGACAGTTAAATCACAACAACAAATTATTGATTCATTCATGAATGAATCAATAATTTGTTGTTGTGATTTAACTGTCATGCGTCGTTCATCCTCCTCACTACAACTTTGACTTTAATCCAGC

• Forward UAP1
  

  GTTTGCGATAACGCTGCCGCTGGATTAAAGTCAAAGTTGTAGTGAGGAGGATGAACGACGCATGACAGTTAAATCACAAC

• Reverse UAP1 (biobrick plasmid)
  

  CAAAAATGGCGATATTATTTAATACTAGTAGCGGCCGCTGCAGTCCGGCAAAAAAGGGCAAGGTGTCACCACCCTGCCCGGGCAGGGTGGTGACACCTTGCCCTTTTTTGCCGGACTGCAGCGGCCGCTACTAGTATTAAATAATATCGCCATTTTTG

The primers for the NAG5 and UAP1 genes worked well, resulting in PCR products of the expected size. However, the AGM1 primers did not result in a PCR product even when used under a variety of conditions. We then altered our cloning strategy and attempeted to use traditional BioBrick assembly. The plasmid containing AGM1 (Bba_K850000) was digested with Spe1 and Pst1, and the product gel-purified and treated with Antarctic phosphatase. The NAG5 gene was cut out of the Bba_K850001 plasmid using Xba1 and Pst1 and gel-purified. These two pieces of DNA were ligated together to produce a plasmid containing the AGM1 and Xba1 parts of the pathway in a BioBrick format. This construct was then cut with Spe1 and Pst1, and the process repeated with the UDP1 gene cut from the Bba_K850002 BioBrick plasmid with Xba1 and Pst1.

This resulted in a plasmid containing the entire pathway (AGM1, NAG5 and UDP1) but no promoter. To test the pathway in Acetobacter, we cut it out of the BioBrick vector using EcoR1 and Pst1 and cloned it into the MCS of pUC18 which has a T7 promoter.

Learn how to design primers from Julie Wolf.

Protocols

Here are some protocols we used in our cloning process.

• Transformation Protocol

Gibson Assembly