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Team:Imperial/Gluconacetobacter
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| - | <p> | + | <p>Bacterial cellulose is used in many areas. However, until now, all bacterial cellulose-based materials have been created using chemical or physical post-production processing, not genetic engineering. This is due to the lack of well-developed tools and methods for Gluconacetobacter genetic engineering, as well as the lack of the genome sequence of the highest cellulose-producing strain ATCC 53582. We have overcome the numerous hurdles associated with G.xylinus genetic engineering, and turned G.xylinus KI and ATCC 53852 strains into new platforms for the production of cellulose-based biomaterials by sequencing the genomes of ATCC 53582 and KI, creating a genetic toolbox of consisting of four new plasmid backbones and 40 widely used genes, and developing a set of new and improved protocols for G.xylinus genetic engineering. </p> |
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Revision as of 00:44, 16 October 2014
Gluconacetobacter
Overview
Bacterial cellulose is used in many areas. However, until now, all bacterial cellulose-based materials have been created using chemical or physical post-production processing, not genetic engineering. This is due to the lack of well-developed tools and methods for Gluconacetobacter genetic engineering, as well as the lack of the genome sequence of the highest cellulose-producing strain ATCC 53582. We have overcome the numerous hurdles associated with G.xylinus genetic engineering, and turned G.xylinus KI and ATCC 53852 strains into new platforms for the production of cellulose-based biomaterials by sequencing the genomes of ATCC 53582 and KI, creating a genetic toolbox of consisting of four new plasmid backbones and 40 widely used genes, and developing a set of new and improved protocols for G.xylinus genetic engineering.
Key Achievements
- Isolated a new strain of Gluconacetobacter from Kombucha tea and characterized its properties fully.
- Sequenced the previously unknown genomes of two G. xylinus strains: cellulose high-producing ATCC 53582 and our Kombucha-isolated strain - which are the first genomes sequenced in the history of iGEM
- Discovered four new plasmids capable of replication in Gluconacetobacter species - pSEVA321, pSEVA331, pSEVA351 and pBAV1K, which replicate both in G. xylinus ATCC 53582 and in our Kombucha-isolated strain
- Created the first transgenic strains of Kombucha-isolated G. xylinus in science
- Using the discovered plasmids, created a genetic toolbox consisting of over 40 genes for G. xylinus engineering and expressed them in the ATCC 53582 and Kombucha-isolated strain
- Developed a set of new and improved protocols for efficient genetic engineering of G. xylinus ATCC 53582 and our Kombucha-isolated strain
- In summary, turned G. xylinus ATCC 53582 and KI strains into new model organisms and developed the necessary tools to create a powerful platform for the synthesis of new cellulose-based biomaterials
Introduction
Due to its high productivity, G. xylinus is the main species used for the production of bacterial cellulose based products. These range from superior wound dressings, artificial blood vessels, scaffolds for tissue engineering, high-quality speaker membranes, stronger paper, nata de coco and many others (Keshk 2014) .
G. xylinus has been the subject of the majority of studies into production of bacterial cellulose. However, research into G. xylinus has primarily focused on the effects of different culture conditions (such as composition of growth media, aeration and agitation) on cellulose productivity, productivity of different strains and different post-processing methods. Few attempts have been made to improve cellulose productivity or the physical properties of cellulose through genetic engineering (but see Chien 2006). Consequently most of the genetic engineering methods and tools available for model organisms, such as E.coli, have not been developed for G. xylinus. These tools must first be developed, in order to begin serious efforts to genetically engineer G. xylinus strains capable of producing novel biomaterials, more cellulose, and at a lower cost.
Aims
Specification
In addition to the lack of tools, the continuous cellulose production of G. xylinus introduces further problems for genetic engineering, as it results in a low growth rate (the division time of G. xylinus is 4 hours, which is 8 times slower than that of E. coli), formation of spontaneous cellulose non-producing mutants in agitated culture (detrimental for the engineering of high-producing strains) and difficulties in performing procedures such as transformation, plasmid DNA extraction, etc. due to the physically interfering cellulose pellicle.
Furthermore, although the highest cellulose-producing strain G. xylinus ATCC 53582 has been used in several studies, the genome sequence of this strain is still unknown, making it impossible to carry out targeted engineering of chromosomal genes, which is vital to achieve increased productivity.
We aim to solve all of these problems, by completing three major projects: sequencing the genomes of ATCC53582 and Kombucha-isolated strain and creating a large toolbox for G. xylinus genetic. We then aim to use these tools to increase and control cellulose productivity and create new biomaterials with wide-ranging properties, by incorporating proteins with different functions into the cellulose matrix (see Functionalisation).
Engineering
Sequencing the genomes of G. xylinus ATCC 53582 and Kombucha-isolated G. xylinus strain
Although genome sequencing has become widely available due to the improvements in next-generation sequencing, even with smaller bacterial genomes (the genome of G. xylinus is approximately 3.5Mbp in size), genome sequencing is still unavailable for small to mid-sized research groups due to high costs. We performed a survey of prices offered by all commercially available service providers using the Illumina MiSeq next-generation sequencing platform (which is the most cost-effective method for bacterial genome sequencing) in Europe, and found that the average costs of fully sequencing a 3.5Mbp genome (which includes library preparation, sequencing, bioinformatics and gap filling) is approximately £3000.
In order to be able to sequence the genome with the limited budget available to our team, we decided to purchase the necessary materials for library preparation and sequencing run, and perform the full sequencing cycle ourselves, from preparing the sequencing library, to analyzing and building the genome from sequencing data. We requested access to and performed the sequencing run on the Illumina MiSeq present at Imperial College’s Genomics Laboratory and completed the genome assembly using (PROGRAM NAMES). For gap filling, we used Sanger sequencing commercially available from Source Biosciences.
Creating a toolbox for Gluconacetobacter genetic engineering
In parallel to sequencing the genome, we began building a large toolbox for G. xylinus genetic engineering. Only a few vectors have been developed for G. xylinus, and most of them were not available for us for various reasons (including patents, materials-transfer agreements, and retired or deceased researchers). For this reason, we first tested out a set of new plasmids, and engineered them to be Biobrick compatible. As some E. coli promoters and proteins have been shown to work in Gluconacetobacter or Acetobacter species (Setyawati, 2007; Chien et al., 2006), and similarly to E.coli, G. xylinus is a Gram- species, we decided to test out and modify already existing Biobricks in the parts registry in G. xylinus. Therefore, the toolkit consists of:
- New, Biobrick compatible shuttle vectors for Gluconacetobacter and E. coli
- pSEVA321
- pSEVA331
- pSEVA351
- pBAV1K
- Characterization and optimization of parts from the Registry, including:
- Fluorescent proteins, GFP, RFP, YFP, CFP
- Chromoproteins
- Vitreoscilla haemoglobin
- The entire Anderson promoter library
- Widely used gene expression control proteins AraC and TetR.
Engineering a high cellulose-producing ATCC 53582 strain
We aim to increase cellulose productivity by inserting the Vitreoscilla hemoglobin gene into G. xylinus and finding the optimum expression level by expressing Vitreoscilla hemoglobin behind different Anderson promoters. (Vitreoscilla haemoglobin was shown to increase cellulose productivity and growth rate by Chien 2006).
Modelling
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Testing
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Results
We have isolated a new strain of Acetobacter from kombucha, and determined its growth rate, cellulose productivity, and natural antibiotic resistance. We have also developed a set of methods for genetic engineering of this strain and have determined five new plasmids capable of replication in this strain. Thus we are the first to genetically engineer it.
We have discovered four new plasmids capable of replication in Acetobacter species - pSEVA321, pSEVA331, pSEVA351 and pBAV1K - both in G.xylinus ATCC 53582 strain, and in the strain we isolated from Kombucha. We have biobricked these plasmids, with the exception of pBAV1K, which had been originally engineered to be biobrick compatible (however, pBAV1K can not be uploaded to parts registry due to binding materials-transfer agreements).
References
