Biofilms: (Re)-programming Adhesion Properties of Bacteria

00:00:11.13 Hi, I'm Alex. I'm part of an international,
00:00:14.08 interdisciplinary group of researchers who've come
00:00:17.08 together to work in the field of synthetic biology.
00:00:19.16 Bacteria can produce proteins called adhesins
00:00:23.28 These allow the bacteria to stick to surfaces and to
00:00:28.28 each other, forming biofilms. Gum disease, catheter contamination,
00:00:34.19 and implant contamination are all medical consequences
00:00:38.18 of biofilm formation. There are also environmental consequences
00:00:42.20 such as metal corrosion. However, if we could control when
00:00:47.24 and where these proteins are expressed, we could use
00:00:50.19 this for good purposes. For example, imagine we have
00:00:55.20 devised a method for extracting an environmental
00:00:59.05 pollutant. We could implement this method into a
00:01:03.22 single bacteria. However, if one of the intermediate substances
00:01:10.02 in the process is harmful to that bacteria, the process can't
00:01:13.22 be carried through. Instead, we could implement several
00:01:18.22 strains of bacteria, each able to carry out a single
00:01:21.23 step in the process, passing along the intermediate substances
00:01:25.00 to the next bacteria. In this way, we could overcome the problem.
00:01:29.02 In order to control what our bacteria sticks to, we removed
00:01:34.25 cell surface proteins such as adhesins and flagella.
00:01:39.17 Into this naked strain, we could implant adhesin genes of
00:01:43.29 our desire. This allows us to control exactly what
00:01:48.10 our bacteria will stick to.
00:01:52.08 Hi, I am Dharmik and this is our experiment.
00:01:56.02 Our strategy is to use a three component protein
00:02:01.06 which can be expressed on the cell surface.
00:02:04.18 A small region on our protein is recognized by the secretion
00:02:08.29 channel and allows it to pass through the inner membrane.
00:02:12.16 When a part of the protein anchors itself through the cellular
00:02:17.13 membrane and feeds the extracellular component out of
00:02:21.11 the cell. The first step in our experiment is to label our
00:02:25.25 naked bacteria so that we can visualize the interactions
00:02:29.20 between cells expressing different adhesins.
00:02:33.13 We transformed the cells with either GFP or mCherry
00:02:39.08 carrying plasmids. To do this, we used two different
00:02:43.19 techniques, mating and electroporation.
00:02:47.19 We utilized a system which transferred the fluorescence genes
00:02:51.16 from the plasmid to the bacterial genome. Now we have
00:02:57.02 one strain which fluoresces green and one red.
00:03:01.04 We checked the fluorescence genes inserted in the correct
00:03:06.07 part of the genome or not using the colony PCR.
00:03:09.24 Now that we have two identifiable strains, we can start
00:03:14.22 thinking about the adhesins. These are the plasmids
00:03:19.04 containing our different adhesins. We are testing two different
00:03:23.00 types of anchor systems. These are the auto-transporters
00:03:27.18 and these are the intimins. We introduced these into our
00:03:33.05 bacteria by electroporation. We then checked that the
00:03:37.05 electroporation was successful by plasmid extraction or
00:03:40.16 PCR. If everything has been successful, we can induce our
00:03:46.00 bacteria to express the adhesins. We can verify correct expression
00:03:51.23 and localization through the cell surface using Western blot and
00:03:56.11 fluorescence microscopy. Hi, I'm Yong.
00:03:59.18 I come from the University of Hong Kong and
00:04:02.06 I'm a member of this synthetic biology team.
00:04:04.25 For this project, there is still a lot of research, interesting
00:04:09.04 research to be undertaken. It would be useful to be able to
00:04:14.05 produce an interesting signal when adhesion occurs.
00:04:18.20 From this, we can start building the complex behavior
00:04:22.17 that is our goal. In a similar manner, linking the expression of
00:04:28.24 the adhesins to more diverse biosensors would enable this
00:04:33.01 system to be useful for many more settings.
00:04:39.08 Being able to direct or at the very least predict,
00:04:43.02 the positioning of adhesins on the cell's membrane
00:04:46.17 would enable more precise community structures, which may
00:04:51.13 improve the importance for certain applications. We are also
00:04:57.25 unsure how many different types of adhesins we can produce
00:05:01.25 in a single cell while maintaining a healthy cell and predictable
00:05:06.20 behaviors. This work will continue, so keep posted.

This Talk

Audience:

Researcher

Recorded: June 2015

Talk Overview

Many bacteria express adhesion proteins that allow them to stick to surfaces and each other, forming biofilms. Biofilms can cause problems such as gum disease and implant contamination. However, by manipulating the adhesion proteins that bacteria express, scientists can control what the bacteria interact with. For example, different strains of bacteria can be engineered to adhere to one another, which might be helpful if several different bacteria are needed in close proximity to break down an environmental contaminant. The participants in the Synthetic Biology in Action course introduced different adhesion genes into a bacterial strain to alter the adhesion properties of the bacteria so that desired traits were expressed on the cell surface.

About the Speaker

Alex Fedorec, PhD student at the University College London

Esteban Martinez Garcia (course instructor), scientist at the Centro Nacional de Biotecnología

Yong Lai, PhD student at the University of Hong Kong

Dharmik Patel, PhD student at the Vellore Institute of Technology, India