Aggregation

Introduction

In our EcoTanker, the goal is to collect objective substance automatically by using E. coli. However, to collect substance, we have to collect the cell at first. So we aimed to construct a device, which signals E. coli to self-aggregate and we focused on a protein, Antigen 43. This protein is derived from E. coli. Antigen 43 consists of two protein subunits, α and β, with apparent molecular masses of about 50 and 53 kDa. The β subunit is attached to the cell surface via interaction with the β subunit, which is an integral outer membrane component (Fig. 1). Antigen 43 has the N-terminal signal peptide and it directs translocation across the cytoplasmic membrane to the periplasm via the general secretory pathway. Subsequently, the β domain forms a β barrel structure in the outer membrane through which the β domain gains access to the cell exterior [1].

Why is this device needed?

Aggregation device is needed because

E. coli

What is this device composed inside it?

This device expresses Antigen 43, which is encoded by the gene agn43. For the promoter, we used OmpR (+) promoter (ompC promoter) (BBa_R0082)(Fig. 2). This promoter responds to phosphorylated OmpR (response regulator). OmpR will phosphorylated by EnvZ, which is a histidine kinase.

How does this device work in EcoTanker?

This device will be activated by the Green light receptor (detail is on the page of PHOTOCONTROL). When we want to collect E. coli, we will flash green light and aggregate it (Fig. 3).

Progress

The wild type of Antigen 43 contains 6 PstI sites. So, to use as a BioBrick, we had to modify this 6 PstI sites. To modify, we choose Overlap PCR and the scheme will be below. First, we amplify 3 fragments by using the genome as a template and primers to modify the PstI sites. Then, by using these 3 fragments as a primer, and the forward and reverse primer when we cloned Antigen 43, we amplified 4 fragments. And we performed overlap PCR with this 4 fragments by using the forward and reverse primer. We confirmed the amplification of the gene of Antigen 43. After digesting this fragment with EcoRI and PstI, ligated to pSB1C3 to construct the plasmid pSB1C3-Antigen 43(BBa_K317008). We analysis the sequence and confirmed that Antigen 43 didn’t have any PstI sites. By using this new BioBrick, we constructed transcriptional unit, generator, and 4 devices. We also submitted these 6 parts as a new BioBrick(Table).

We confirmed the function of Antigen 43 by using 2 devices that expresses Antigen 43 constitutively and evaluate by measuring OD660 approximately 1 cm from the top [1]. The methods will be, inoculate a singe colony to 5 ml of LB medium and incubate at 37℃ over night. Then, stopped incubation and stand the culture solution. Then, measured the OD660 from the top of 1 cm of the culture. The results of measuring OD660 (Fig. 5) and a picture of appearance of E. coli sinking will be shown below (Fig.5). From the results, the E. coli that harbors the plasmids (Constitutive promoter-RBS-Antigen 43-Double terminator) show decreasing of OD660 although the strength of the promoter is weak (BBa_J23102 is strong and BBa_J23109 is weak). So, we can say low expression of Antigen 43 will be enough to sink the E. coli.

BioBricks we submitted are bellows.

References

[1] KRISTIAN KJÆRGAARD, MARK A. SCHEMBRI, HENRIK HASMAN, AND PER KLEMM. Antigen 43 from Escherichia coli Induces Inter- and Intraspecies Cell Aggregation and Changes in Colony Morphology of Pseudomonas fluorescens JOURNAL OF BACTERIOLOGY, 2000, p. 4789–4796, Vol. 182, No. 17

Team:Tokyo-NoKoGen/Project/aggregation

From 2010.igem.org