Team:UC Chile/Bactomithril

Overview

Spider dragline silk is an exceptionally strong and elastic fiber and is an ideal material for numerous biomedical and industrial applications. In this secondary project we developed a novel secretion system that allows to export proteins to the extracellular medium and tried to add the first spider-silk biobrick to the Registry. This biobrick would have the synthetic silk gene ADF-3 from the orb weaving spider Araneus diadematus. Nevertheless, due to the repetitive nature of the spider silk monomer we could not finish this biobrick for de Regional Jamboree (despite of several intents and strategies). </p>

Introduction

Spider dragline silk is an exceptionally strong and elastic biomaterial and one of the strongest natural fibers known. It is five times stronger by weight than steel and three times tougher than the top quality man-made fiber Kevlar [1]. That’s why is referred to as “biosteel”. Furthermore, this material is biocompatible, biodegradable and has potential for processing in aqueous solution under ambient conditions.

These properties make the spider silk an ideal material for numerous industrial applications such as bullet-proof vests, parachutes, seat belts and composite materials in aircraft, and a promising substance for biomedical applications such as drug delivery systems and scaffolds for tissue engineering.

The excellent mechanical properties and low immunogenicity of spider webs have fascinated the man for thousands of years, but unfortunately large scale farming of spiders is not convenient because of the highly territorial and aggressive character of these arthropods. Synthetic spider silk production is a promising way to make use of this exceptional biomaterial.

Construct: a novel secretion system

Working Plasmid

GFP Reporter Plasmid

Protease Producer Plasmid

Animation describing the first secretion system

Notebook

In this section you will find the complete description of our work in this project.

Results

Experiment 1

We transformed E. Coli with our GFP Reporter Plasmid (B2) and with the Protease Producer Plasmid (B3). We did a little experiment with those bacteria.

The following samples were prepared:

B2

B2+

B2+ & B3

B2+ & supB3

Nomenclature

B2- (coli transformed with GFP Reporter Plasmid)

B2+ (coli transformed with GFP Reporter Plasmid, induced with Arabinose)

B3+ (coli transformed with Protease Producer Plasmid, induced with Arabinose)

supB3+ (supernatant of coli transformed with Protease Producer Plasmid induced with Arabinose)

Then we observed each sample with an epifluorescence microscope. The results were promising. B2- did not express sfGFP, but B2+ did. Additionally, in both cases (B2+ & B3) and (B2+ & supB3) the fluorescence of sfGFP disappeared almost completely.

Experiment 2

We prepared for second time samples of B2+ & B3+ to observe in the epifluorescence microscope the effect of time in the samples.

This time B2+ & B3+ presented much more fluorescence, and it persisted over time (at least 1 hour with no significant variation).

Experiment 3

We did another experiment to investigate the interactions between our bacteria B2+ and B3, but this time with a serious protocol and recording the data for later analysis.

We expected that our results were coherent with our theory. [1]. Both HIV protease and protease K should be able to cut the HIV cleavage site, releasing the sfGFP.

The samples used this time were:

B2+ :

E. coli transformed with GFP Reporter Plasmid and induced with Arabinose

B2+ / SN B3+ :

E. coli transformed with GFP Reporter Plasmid and induced with Arabinose, and Supernatant of coli transformed with Protease Producer Plasmid induced with Arabinose

B2+ / SN B3- :

E. coli transformed with GFP Reporter Plasmid and induced with Arabinose, and Supernatant of coli transformed with Protease Producer Plasmid not induced with Arabinose

B2+ / protease K :

E. coli transformed with GFP Reporter Plasmid and induced with Arabinose, and protease K.

Subsequently we proceeded to observe the samples in an epifluorescence microscope. In the following figure you can see one micrograph of each sample at 100x.

Additionally, we analyzed 4 micrographs of each sample (n=4) with the software ImageJ to compare their fluorescence intensity.

All the different treatments presented significant differences, except (B2+ & protease K) and (B2+). Remarkable is the difference between (B2+ / SN B3+) and (B2+ / NS B3-). Also, the direct application of protease K over the samples decreased even more the fluorescence. However, the low fluorescence of B2+ is very weird. We will have to repeat this experiment, but at least the major part of the results makes is what we expected.

Experiment 4

We repeated the experiment to investigate the interactions between our bacteria B2+ and B3+ with a serious protocol and recording the data for later analysis. This time we added the control B2-.

In the following figure you can see one micrograph of each sample at 100x obtained from a fluorescence microscope.

In the figure each row represents one sample. The first row contains the micragraphs with UV filter. The second row contains the micrographs seen with light. The third row contains the previous micragraphs overlayed (the light image is in grayscale, and the UV image has its black background removed). The forth image is an amplification of the third image (1:4 ratio). Click over the image to open it in a higher resolution.

Additionally, we analyzed 4 UV micrographs of each sample (n=4) with the software ImageJ

The results were quite different compared to the ones of our previous experiment. Remarkable is that, as expected, B2- and B2+ present the lowest and highest fluorescence intensity. Additionally, (B2+ & B3+) and (B2+ & Protease K) present very similar fluorescence. However, for second time we obtained a weird result: (B2+ & B3+) and (B2+ & B3-) present the same amount of fluorescence.

In conclusion, we know that sfGFP expresses in our e. coli. But we don’t know if it is attached to the external side of the membrane, or if the HIV-1 protease works as expected. As this secretion system seems to be failing, we chose to try other alternatives.

The construction of the first spider silk biobrick

We tried with a lot of patience (in SEVERAL intents with many different strategies) to make a biobrick with the spider silk monomer ADF-3 or the sequence of DNA corresponding to ADF-3 and tags necessary to identify and export the protein with the Type 3 Secretion System of Salmonella (SPI 2). The original sequences correspond to the described in

Widmaier, D. M., Tullman-Ercek, D., Mirsky, E. a, Hill, R., Govindarajan, S., Minshull, J., & Voigt, C. a. (2009). Engineering the Salmonella type III secretion system to export spider silk monomers. Molecular systems biology, 5(309), 309. doi:10.1038/msb.2009.62

This sequence was kindly sent by Dr. Christopher Voigt to us.

A detailed description of this work is in the notebook section. After tons of hours of hard work, when finally PCR amplified bands of the correct size, the digestion tests were positive, Colony PCR were succesful, and Gibson Assemblies seemed to work, we sent our final sequence for sequencing, but the results did not match with our designs. Probably this is due to the hihgly repetitive nature of the spider silk monomers.