Team:CIDEB-UANL Mexico/project union

E. coli needs to resist saline environments, UV rays and temperature changes in order to capture Na+ ions, and produce an aroma as a reporter, everything in the water. That is why it is necessary to remove E. coli from the water in order to obtain usable water; through a biofilter it was easy to do. We choose silica as the material for our biofilter, so we make that E. coli expressed a membrane protein which could have the ability for binding silica, and in that way remove E. coli from the water. This was possible for the circuit created by UANL Mexico 2012 team; they created a circuit to make E.coli attached to silica, but as they did not prove it, we want to determine if it really works or not.

How is composed?

The binding circuit consists mainly in a fusion protein (a set which includes the CDS L2 with its peptide signal and AIDA) in order to make the protein for binding silica, a membrane protein. In that way E. coli would attach to silica.

How act L2 and AIDA together?

The gene L2 encodes for a protein able to attach to silica. Taniguchi et al. reported in 2007 that the L2 ribosomal protein from E. coli strongly adsorbs to silica surfaces, up to 200 times tighter than poliarginine tags commonly used for protein purification. In their work, Taniguchiet al. 2007, constructed a fusion protein of L2 and green fluorescent protein (GFP) which adsorbed to a silica surface even after washing for 24 hours with a buffer containing 1 M NaCl (Figure 3).

AIDA-I is an E. coli membrane protein with a passenger domain of 76 kDa exposed to the extracellular space and a transmembrane beta-barrel domain of 45 kDa; the latter has been used to express functional proteins in the cell-membrane of up to 65 kDa (van Bloois et al., 2011). Furthermore passengers coupled to AIDA-I have been reported to reach an expression level of more than 100,000 copies per cell in the outer membrane (Jose and Meyer, 2007). AIDA-1 allows the expression of proteins larger than small peptides in the outer membrane what makes it the best option to use with L2.

How much is important to use BgIII and BamHI to link L2 and AIDA-I?

In order to make a fusion protein we cannot use SpeI and XbaI to join them because the reading frame would change making a completely different protein. So in order to avoid such problem we use BgIII and BamHI instead which can join AIDA and L2 without changing the reading frame. The scar produced between BamHI and BgIII, as is shown in the figure 2, is formed by six bases respecting the reading frame from both proteins in order to synthetize the correct protein.

Parts of the module

	Promoter: BBa_J23119 A promoter refers to the part that initiates the gene transcription. In addition a constitutive promoter refers to promoters that are continuously working. Parts J23100 through J23119 are a family of constitutive promoter parts isolated from a small combinatorial library. The J23119 is the most effective and common constitutive promoter from them. In the specific case of our bacteria, it helps to continuously transcribing the L2+AIDA gene. This promoter has a length of 35bp.
	RBS: BBa_B0034 A RBS part refers to the place where a bacterial ribosome will initiate the translation of mRNA of a specific gene. This specific is RBS based on Elowitz repressilator. It has a length of 12 pb.
	CDS: BBa_K888000 This CDS gives the property for binding silica and glass surfaces to E. coli. The binding of this protein to silica surfaces does not require chemical modification, pre-treatment or any specific conditions (Taniguchi et al. 2007). It has a length of 819 bp.
	CDS: BBa_K888001 AIDA-I is synthetized as a 132 kDa pre-protein featuring a signal peptide which is cleaved during transport trough the inner membrane, a 78 kDa adhesin (passenger) domain, and a 45 kDa translocator. This autotransporter has a large capability in translocating relatively large passengers from 12-65 kDa by showing a N-terminal type of fusion. Coupled with a passenger domain and a signal peptide (K888005), it is possible to express functional proteins in the outer membrane of E. coli. It has a length of 1482 bp.
	CDS: BBa_K888005 When this part is coupled with a passenger attached to AIDA-I translocator domain (K888001), it is possible to express functional proteins in the outer membrane of E. coli. The signal peptide is naturally cleaved during transport trough the inner membrane (Li et al. 2007; van Bloois et al. 2011).It has a length of 147 bp.
	Terminator: BBa_B1002 Part made of 6bp, responsible for stopping transcription.

Other teams that used it:

UANL México 2012: They proposed the fusion protein for using it to binding silica after detect and capture arsenic acid in groundwater, and in that way removed the pollutant arsenic acid from the water, as part of water bioremediation, but they did not finish it. That is why we want to determine if it will work.

How to create a biofilter?

Although E.coli could acquire the ability for binding silica, we need to create a biofilter to remove bacteria from water. Our proposal as biofilter is shown in the next figure:

References

Part BBa_K888000 (2012). Retrieved on March 29th, 2014, from: http://parts.igem.org/wiki/index.php?title=Part:BBa_K888000.

Part BBa_K888001 (2012). Retrieved on March 29th, 2014, from: http://parts.igem.org/wiki/index.php?title=Part:BBa_K888001.

Part:BBa_B0034. (2013). Retrieved on March 30th, 2014, from: http://parts.igem.org/wiki/index.php?title=Part:BBa_B0034.

Part:BBa_J23119. (2006). Retrieved on April 30, 2014, from: http://parts.igem.org/wiki/index.php?title=Part:BBa_J23119.

Part BBa_K888005 (2012). Retrieved on March 29th, from: http://parts.igem.org/wiki/index.php?title=Part:BBa_K888005.

UANL Mexico (2012). Recovery module. Retrieved on March 28th, from: https://2012.igem.org/Team:UANL_Mty-Mexico/Project/recovery.