Multicellular behavior

M. mnthus development. The key to bacterial coordinated behavior resides in the ability of a cell to receive, interpret, and respond to these signals. Relaying the information may require direct contact between the donor and the recipient cells or it may be carried out from a distance, i.e., by means of diffusible molecules, which are detected through their interaction with specific receptors. As discussed in Chapter 3, bacterial chemotaxis is the most completely understood of the bacterial sensory transduction systems. While the role of chemotaxis in intercellular communication is still not clear, in some cases, mutants deleted for chemotaxis genes fail to carry out one or another of the processes mentioned above. Components of the chemotaxis system seem to play a role in swarming motility, pattern formation, and myxobacterial development. In fact, it appears that certain chemotaxis functions have been recruited by certain species to mediate intercellular communication. In this chapter, we review some examples, and provide evidence as well as hypotheses concerning a role for proteins and systems involved in chemotaxis in multicellular behavior. 

Thus, chemotaxis gene products are involved in two very different modes of multicellular behavior in E. coli and Salmonella swarming motility and the complex pattern formation discussed above. 

Belas, R., Ersldne, D. and Flaherty, D. (1991). Proteus mirahilis mutants defective in swarmercell differentiation and multicellular behavior. J. Bacterial. 173,6279-6288. 

Eberl, L., dnson, M.K., Sternberg, C., Stewart, G.S.A.B., Christiansen, G., Chabra, S.R., Daykin, M., WiUiams, R, Mohn, S. and Givskov, M. (1996). Involvement of N- acyl-L-homoserine lactone autoinducers in controlling the multicellular behavior of Serratia liquefaciens. Mol. Microbiol. 20, 127-136. 

Kleerebezem, M. and Quadric, L.E. (2001). Peptide pheromone-dependent regulation of antimicrobial peptide production in gram-positive bacteria a case of multicellular behavior. Peptides 22, 1579—1596. 

Hooshangi, S., Bentley, W.E., 2008. From unicellular properties to multicellular behavior bacteria quorum sensing circuitry and applications. Curr. Opin. Biotechnol. 19, 550-555. 

The enormous structural variety and functional capacity of multicellular organisms is due to their ability to coordinate the biochemical reactions of the various cells of the total organism. The basis for this coordination is the intercellular communication, which allows a single cell to influence the behavior of other cells in a specific manner. 

For many years, before the concept of recombinant DNA, scientists postulated that bacteria were unicellular microbes. In more recent yeans, the unicellular structure and. notably, the unicellular behavior of bacteria has been subjected to serious questions by a number of scientists. As observed by Shapiro, Investigators are finding that in many ways an individual bacterium is more analogous to a component cell of a multicellular organism than it is to a free-living autonomous organism. There is... 

The organismal division of labor that resulted from the development of multicellularity brought about behavioral repertoires that, by the standards of single-celled life forms, can be considered complex. The study of the organismal, cellular, and molecular ways in which environmentally encountered chemical signals influence behaviors associated with feeding, development, and social interactions has made important contributions to our understanding of chemoreception. 

In multicellular organisms, the space between cells is largely occupied by an intricate network of interacting macromolecules that constitute the extracellular matrix. This matrix surrounds, supports and regulates the behavior of the cells, such as fibroblasts, that secrete the extracellular matrix. Together, the matrix with these cells constitutes the connective tissue. 

Finally, part (c) represents that part of metabolism in which energetic molecules (ATP and reductants) are used to synthesize new cells, or repair existing cells. As with the other categories, the enzymes and genes involved with these processes are easily recognizable across domain boundaries. In this category lie the anabolic reactions that lead to complex cells, multicellular organisms, tissues, and behavioral biominerals, all characteristic of the Eukarya. 

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