Bacterial patterns
Encyclopedia
The formation of patterns
in the growth
of bacterial colonies has extensively been studied experimentally. Resulting morphologies appear to depend on the growth conditions. They include well known morphologies such as dense branched morphology (DBM) or diffusion-limited aggregation
(DLA), buch much complex patterns and temporal behaviour can be found.
A large number of studies on pattern formation in bacterial colonies have been performed in Bacillus subtilis
and in Proteus mirabilis
.
Mathematical modeling of colony growth can reproduce the observed morphologies and the effect of environmental changes. Employed models include:
on a Petri dish
can grow under controlled conditions. By varying agar
concentration (which permits the control of the hardness of the medium), and the nutrient
concentration, the response of the colony to external stresses can be studied. The different morphologies appear in the following growth conditions:
High nutrients level, hard medium: Eden-like growth http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_eden.htm
High nutrients level, semi-soft hardness of medium: Periodical growth forming concentric rings http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_concentric.htm
High nutrients level, soft medium: homogeneous, disk-like growth http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_fisher.htm
Low nutrients level, hard medium: DLA growth http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_dla.htm
Low nutrients level, soft medium: DBM growth http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_dbm.htm
A complete morphological diagram can then be drawn by varying growth conditions. http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/Bacillus.jpg
These different morphologies can be obtained from a reaction-diffusion model. This kind of model is useful to asses which mechanisms are relevant for the different morphologies. The complete morphological diagram can be obtained by using two fields, density of bacteries and nutrient concentration, and taking into account that bacteries can increase motility in response to adverse external conditions. That means that diffusion in the medium and the response of bacteria are the relevant factors in this particular case.
Pattern formation
The science of pattern formation deals with the visible, orderly outcomes of self-organisation and the common principles behind similar patterns....
in the growth
Bacterial growth
250px|right|thumb|Growth is shown as L = log where numbers is the number of colony forming units per ml, versus T Bacterial growth is the division of one bacterium into two daughter cells in a process called binary fission. Providing no mutational event occurs the resulting daughter cells are...
of bacterial colonies has extensively been studied experimentally. Resulting morphologies appear to depend on the growth conditions. They include well known morphologies such as dense branched morphology (DBM) or diffusion-limited aggregation
Diffusion-limited aggregation
Diffusion-limited aggregation is the process whereby particles undergoing a random walk due to Brownian motion cluster together to form aggregates of such particles. This theory, proposed by Witten and Sander in 1981, is applicable to aggregation in any system where diffusion is the primary means...
(DLA), buch much complex patterns and temporal behaviour can be found.
A large number of studies on pattern formation in bacterial colonies have been performed in Bacillus subtilis
Bacillus subtilis
Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...
and in Proteus mirabilis
Proteus mirabilis
Proteus mirabilis is a Gram-negative, facultatively anaerobic, rod shaped bacterium. It shows swarming motility, and urease activity. P. mirabilis causes 90% of all Proteus infections in humans.-Diagnosis:...
.
Mathematical modeling of colony growth can reproduce the observed morphologies and the effect of environmental changes. Employed models include:
- Reaction–diffusion systemReaction–diffusion systemReaction–diffusion systems are mathematical models which explain how the concentration of one or more substances distributed in space changes under the influence of two processes: local chemical reactions in which the substances are transformed into each other, and diffusion which causes the...
- Cellular automata
Colonies of Bacillus subtilis
Colonies of Bacillus subtilisBacillus subtilis
Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...
on a Petri dish
Petri dish
A Petri dish is a shallow glass or plastic cylindrical lidded dish that biologists use to culture cells or small moss plants. It was named after German bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch...
can grow under controlled conditions. By varying agar
Agar
Agar or agar-agar is a gelatinous substance derived from a polysaccharide that accumulates in the cell walls of agarophyte red algae. Throughout history into modern times, agar has been chiefly used as an ingredient in desserts throughout Asia and also as a solid substrate to contain culture medium...
concentration (which permits the control of the hardness of the medium), and the nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
concentration, the response of the colony to external stresses can be studied. The different morphologies appear in the following growth conditions:
High nutrients level, hard medium: Eden-like growth http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_eden.htm
High nutrients level, semi-soft hardness of medium: Periodical growth forming concentric rings http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_concentric.htm
High nutrients level, soft medium: homogeneous, disk-like growth http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_fisher.htm
Low nutrients level, hard medium: DLA growth http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_dla.htm
Low nutrients level, soft medium: DBM growth http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/B_dbm.htm
A complete morphological diagram can then be drawn by varying growth conditions. http://www.phys.chuo-u.ac.jp/labs/matusita/images/BacteriaFig/Bacillus.jpg
These different morphologies can be obtained from a reaction-diffusion model. This kind of model is useful to asses which mechanisms are relevant for the different morphologies. The complete morphological diagram can be obtained by using two fields, density of bacteries and nutrient concentration, and taking into account that bacteries can increase motility in response to adverse external conditions. That means that diffusion in the medium and the response of bacteria are the relevant factors in this particular case.
External links
Some more images of patterns in bacterial growth can be found in:- http://www.genomenewsnetwork.org/articles/05_03/stress_art.shtml
- http://star.tau.ac.il/~eshel/gallery.html