The formation of patterns in the

growth Growth may refer to: Biology * Auxology, the study of all aspects of human physical growth * Bacterial growth * Cell growth * Growth hormone, a peptide hormone that stimulates growth * Human development (biology) * Plant growth * Secondary grow ...

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 Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...

(DBM) or

diffusion-limited aggregation Diffusion-limited aggregation (DLA) 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 T.A. Witten Jr. and L.M. Sander in 1981, is a ...

(DLA), but 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'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus '' Baci ...

'' and in ''

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. It is widely distributed in soil and ...

''.

Mathematical modeling A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used in the natural sciences (such as physics, ...

of colony growth can reproduce the observed morphologies and the effect of environmental changes. Employed models include: *

Reaction–diffusion system Reaction–diffusion systems are mathematical models which correspond to several physical phenomena. The most common is the change in space and time of the concentration of one or more chemical substances: local chemical reactions in which the s ...

Cellular automata A cellular automaton (pl. cellular automata, abbrev. CA) is a discrete model of computation studied in automata theory. Cellular automata are also called cellular spaces, tessellation automata, homogeneous structures, cellular structures, tessel ...

Colonies of Bacillus subtilis

Colonies of

on a

Petri dish A Petri dish (alternatively known as a Petri plate or cell-culture dish) is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured,R. C. Dubey (2014): ''A Textbook Of Biotechnology For Class-X ...

can grow under controlled conditions. By varying

agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori ('' Gracilaria'') and "tengusa" ('' Gelidiaceae''). As found in nature, agar ...

concentration (which permits the control of the hardness of the medium), and the

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excr ...

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 growt

;High nutrients level, semi-soft hardness of medium: Periodical growth forming concentric ring

;High nutrients level, soft medium: homogeneous, disk-like growt

;Low nutrients level, hard medium: DLA growt

;Low nutrients level, soft medium: DBM growt

A complete morphological diagram can then be drawn by varying growth conditions

These different morphologies can be obtained from a reaction-diffusion model. This kind of model is useful to assess which mechanisms are relevant for the different morphologies. The complete morphological diagram can be obtained by using two fields, density of bacteria and nutrient concentration, and taking into account that bacteria 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.

References

* Experiments on Bacillus subtilis by Matsushita et al. *{{cite journal , last=Lacasta , first=A. M. , last2=Cantalapiedra , first2=I. R. , last3=Auguet , first3=C. E. , last4=Peñaranda , first4=A. , last5=Ramírez-Piscina , first5=L. , title=Modeling of spatiotemporal patterns in bacterial colonies , journal=Physical Review E , publisher=American Physical Society (APS) , volume=59 , issue=6 , date=1999-06-01 , issn=1063-651X , doi=10.1103/physreve.59.7036 , pages=7036–7041, arxiv=cond-mat/9904367 Reaction-diffusion model for Bacillus Subtilis.

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 Bacteriology