Team:NRP-UEA-Norwich/BioBricks
BIOBRICKS
In order to assess whether our BioBricks would function in our chassis organism Shewanella oneidensis MR-1 we attempted to transform and express two BioBricks into S. oneidensis MR-1; J04450 containing a gene for the red fluorescent protein (RFP) and K584001 which contains a gene for the green fluorescent protein (GFP). These BioBricks were chosen as they contain reporter genes and successfully transformed colonies could be easily identified under UV light.
As S. oneidensis MR-1 are not amenable to heat shock transformation we took a tri-parental conjugation approach. We followed protocol 2:1. Parent Escherichia coli strains were transformed with J04450 and K584001 respectively using a heat shock approach according to protocol 0.2. For step 9 chloramphenicol was used instead of kanamycin as we were working with BioBricks and these contain chloramphenicol as a selective marker, not kanamycin. Carbenicillin was still used to select against E. coli parent and helper strains as S. oneidensis have natural resistance to this antibiotic.
After serial dilutions for all attempted conjugations no individual S. oneidensis MR-1 colonies survived, and therefore the cells failed to display chloramphenicol resistance. Escherichia coli parent and helper strains survived, so carbenicillin resistance was successfully transferred from S. oneidensis MR-1 to E. coli. This indicated conjugation must have been successful, however S. oneidensis MR-1 failed to display chloramphenicol resistance. As the promoters for the antibiotic resistance genes are constitutive the genes should have been transcribed if present. The origin of replication of these plasmids however, pMB1, have not been used in S. oneidensis MR-1 by past iGEM teams. The Harvard 2008 iGEM team did not list pMB1 as an effective origin of replication for plasmids in S. oneidensis MR-1. Additionally NTU Singapore in 2015 used the pHG101 plasmid which has a different origin of replication to allow for expression of their BioBrick part in S. oneidensis MR-1. Similarly as a result of our failure to express functional BioBricks in S. oneidensis MR-1 we decided to transfer our gene cluster to a modified pBAD vector using a golden gate cloning strategy. Our bio-bricks were designed to assemble the entire gene cluster for each separate hydrogenase into a single expression vector.
In the future iGEM teams should investigate this to confirm the origin of replication is in fact the issue with BioBrick expression in S. oneidensis MR-1. If this is in fact the case future iGEM teams can then move on to apply synthetic biology to optimise the origin of replication of some BioBricks for the highest possible copy number in S. oneidensis MR-1. These can then serve as a backbone for the cloning of further genes to be expressed in S. oneidensis MR-1. This exercise will compound in value as this organism becomes more widely used for synthetic biology.
https://2008.igem.org/Team:Harvard
https://2015.igem.org/Team:NTU-Singapore
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