Patterns of Bacterial Growth

Introduction

For the purposes of identifying patterns of growth, bacteria colonies can be through of as multicellular organisms. (info about communication)

Patterns of growth are a result of bacteria adapting their behavior to suit their environment.

Bacteria in the lab are grown specifically to isolate single colonies. Bacteria in the wild must cope with environmental conditions.

There are three main patterns of growth as described by Prof. Eshel Ben-Jacob of Tel-Aviv University: fine radial branches, branching patterns, and dense fingers.

An agar plate demonstrating bacteria with strong chirality. Image courtesy of the laboratory of Prof. Eshel Ben-Jacob of Tel-Aviv University.

Diffusion-Limited Aggregation

Example of random walker movement and the first steps DLA lattice formation. Courtesy of Yale University.

Diffusion-Limited Aggregation (DLA) is a growth model that results in complex, multi-branched forms. It can be applied to any system where diffusion is the main method of particle transportation. It can be observed in bacterial growth on agar plates, dendrites, dust balls, electrodeposition, and mineral deposits.

To form a DLA pattern, begin with a seed molecule at the origin of the lattice. A "random walker" molecule diffuses from far away in a random pattern of motion. It stops once it reaches a space adjacent to the seed molecule, and another random walker is launched. In a DLA lattice, a molecule that sticks out of a main branch will not be rounded or smoothed over by new growth, but rather emphasized. Nodes are more likely to catch wandering particles because they three facets available for growth, compared to a molecule in the branch, which only has one facet.

Agar Density

As agar density increases, the width of branches found in the fractal pattern of bacteria growth is thinner.

P is peptone level. Nc is related to agar concentration.

Nutrient Density

Bacterial growth patterns are compact at high nutrient densities, and become more fractals and peptone density decreases.

Intercellular Communication

Length of cells and handedness of flagella also affect how patterns form.

Conclusion

Overall text length should be at least 1,000 words (before counting references), with at least 2 images. Include at least 5 references under Reference section.

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Matusushita, M., and Fujikawa, H. "Diffusion-Limited Growth in Bacterial Colony Formation". Physica A: Statistical Mechanics and its Applications. 1990. Volume 168, Issue 1, p. 498–506.

Eshel Ben-Jacob (1997) From snowflake formation to growth of bacterial colonies II: Cooperative formation of complex colonial patterns, Contemporary Physics, 38:3, 205-241

Witten, T. A., and Sander, L. M. "Diffusion-limited aggregation". Physical Review B. 1983. Volume 27, Number 9. p. 5686-5697.

Edited by Eleanor Lopatto, student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2013, Kenyon College.