Characterization of a transcriptional response to population density in Bacillus subtilis

Bacteria keep track of their population density by using extracellular signaling molecules. In response to the accumulation of these signals, changes in gene expression coordinate the switch from unicellular activity to group behavior. In Bacillus subtilis, this shift towards social behavior occurs, in part, through a signaling pathway that monitors the concentration of the ComX pheromone. ComX stimulates the receptor ComP which activates the transcription factor and response regulator ComA, resulting in the regulation of competence development and other processes. I characterized the signaling pathway and the ComA-mediated cellular response by examining global changes in gene transcription. Under the conditions tested, the ComX-P-A pathway is linear; the ComX pheromone acts exclusively on the ComP membrane histidine kinase receptor, which in turn only activates the response regulator ComA. I found that the activation of the ComX-P-A pathway leads to changes in expression of at least 35 transcriptional units; nine of them appear to be directly regulated by ComA. Many of the operons encode genes that affect the membrane and extracellular environment. The signaling pathway positively regulates transcription of genes involved in fatty acid metabolism, antibiotic production, exopolysaccharide biosynthesis, and degradative enzymes. The presence of signal sequences suggests that more than half of the ComA-dependent gene products of unknown function are membrane or extracellular in nature. These physiological changes may allow B. subtilis to become more resistant to the accumulation of toxic products, scavenge alternative nutrient sources, and eliminate possible competitors for those new nutrients.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Biology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Comella, Natalia, 1974-

Advisor dc:contributor.advisor

• Alan D. Grossman.

• Biology.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/30069

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/30069