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Revision as of 17:19, 5 August 2005

Intro

To have some 3D population of bacteria build structures with certain (stochastic?) patterns/regularities.

Principle

Quorum sensing and some fancy cascades triggered when some threshold is reached, leading to the excretion of substances that will add up to structures (or some other interesting phenomena).

The "Encapsulation" approach

Basic Concept

Assume the bacteria population starts with the slow but steady production of A, which diffuses into the vicinity and can be sensed by other bacteria (Quorum Sensing). When a critical threshold is reached within a bacterium, a cascade is triggered (nothing new there). The cascade consists of a short but intensive production of B (which stays inside the individual as long as it is intact) while ceasing the production of A, and a delayed aptosis (suicide). It is very likely, that the process is stochastic, i.e. that due to differences in individual sensitivity and in local concentration (which is probably true if the suspension is not stirred) some bacteria will be first, while others will never sense a critical threshold of A and thus never start the cascade. Probably, A and B will both need to degrade rather quickly. While A now is no longer produced around the bacteria in the death cascade, B is suddenly present in hopefully high concentrations in its vicinity when it dissolves during apoptosis. The survivors that have not reached the threshold of A to trigger a cascade themselves, will now react to B and start to excrete some substance C, which will harden to some structure that will most likely form spheres or some very porous structure.

As a construction material, maybe we could try to use bacteria that produce bio-plastics such as Polyhydroxyalcanoate (PHAs/PHBs)?

Possible Extensions

Encapsulation of Drugs and Particles

Assuming that the behavior described above will actually to the formation of small spheres encapsulating the area the cascading cells formerly occupied, one could use this to encapsulate specific substances or nano-particles. Such an effect could be useful to produce capsules filled with drugs or other agents or some cleaning behavior removing certain substances or physical particles from a solution. Obviously, then additional mechanisms have to be designed to either produce a specific drug (if not identical with B) or sense such a nano-particle and starting a cascade.

Aggregation Behavior

Maybe B should also lead to the aggregation behavior, i.e. cells attaching to other cells currently producing B (or a new substance D for this purpose that is produced in parallel with D). This could ensure a critical size of such a sphere.

Challenges

• The dynamics are not entirely trivial, I guess, especially if not tuned well, and thus what structures will actually emerge.
• I obviously have no clue about what is really possible biologically speaking, especially with the excretion of hardening materials in order to build structures.

Implementation Strategies

• PHB/PHA: (see review sudesh00).

The problem of polyhydroxyalkanoates is that they are not secreted, but they build inclusion bodies inside the cells. This problem could be solved if the cells would also produce exopolysaccharides (e.g. xanthan, gellan, bacterial alginate). These can be either associated with the cell surface in the form of capsules or secreted in the form of slime so that a kind of slime-gel is formed around the cells. When the PHA/PHB producing cells will lyse (die), PHA/PHB could be released but would (hopefully) be entrapped in this kind of gel clot.

• Upregulated cell wall (Peptidoglycan or Murein) production?

• Cellulose production:

Bacterial cellulose is produced as water-insoluble, 80% crystalline (plant cellulose only 50-60%) microfibrils. Cellulose fibrils can interact with each other through hydrogen-bonding, thus forming extended stuctures, visible as a mat atop the bacteria :-)!!!! In cellulose-producing E.coli it is produced concomitantly with aggregative fimbriae (AGF)(important components of extracellular matrix of multicellular morphotypes), creating an highly inert hydrophobic extracellulat matrix around the aggregates of cells (flocs) (see reviews römling02, ross91)

Discussion

>> for comments, questions and temporary remarks go to the Talk:Constructor_Bacteria

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