Document Type

Honors Capstone Project

Date of Submission

Spring 5-1-2007

Capstone Advisor

Dr. Anthony Garza

Honors Reader

Dr. Roy Welch

Capstone Major


Capstone College

Arts and Science

Audio/Visual Component


Capstone Prize Winner


Won Capstone Funding


Honors Categories

Sciences and Engineering

Subject Categories

Biochemistry | Biochemistry, Biophysics, and Structural Biology


Myxococcus xanthus is a soil bacterium that is a member of a group of organisms known as the myxobacteria. M. xanthus cells live in biofilms and feed on other bacteria to obtain nutrients. During times of inadequate nourishment, M. xanthus cells aggregate, build fruiting bodies, and fruiting body cells differentiate into spores that are highly resistant. In order to form the fruiting bodies, M. xanthus cells must be able to move across solid surfaces. There are two motility systems, the adventurous system (A-motility) and the social system (S-motility), used by M. xanthus cells to navigate across surfaces. The adventurous system controls movement of individual cells, while the social system controls the movement of multi-cellular groups. In addition to surface motility, the development of fruiting bodies relies on largescale changes in gene expression that are coordinated by the production of cell-cell signals. There are five known signals involved in M. xanthus fruiting body formation and the two cell-cell signals that have been characterized in the most detail are A-signal and C-signal. A-signal acts very early in development and it functions as diffusible cell density signal. C-signal acts after A-signal and it is important for aggregation and sporulation. C-signal controls the positioning of densely packed cells and requires cell-to-cell contacts to function properly. These signals help M. xanthus cells coordinate transcription of developmentally regulated genes. In M. xanthus, expression of many developmentally regulated genes is controlled by σ54 promoters and NtrC-like activator proteins. Transcription from σ54-promoter elements is dependent upon the transcription factor σ54, which directs RNA polymerase to promoter recognition sites. However, σ54-RNA polymerase is trapped in a closed promoter complex and is, therefore, unable to activate transcription. In order to form an open promoter complex and begin transcription, σ54-RNA polymerase utilizes enhancer binding proteins as activators. These enhancer binding proteins are called NtrC-like activators. NtrC-like activators bind DNA sequences located upstream of σ54-RNA polymerase binding sites and use the energy from ATP hydrolysis to help σ54-RNA polymerase activate transcription. These proteins are important components in the machinery that regulates transcription of M. xanthus developmental genes. Fifty three M. xanthus genes code for NtrC-like activator proteins and 16 of these genes are known to be important for the developmental process. Five uncharacterized genes have been inactivated to test for defects in motility and development. Mutations in three activator genes caused defects in surface motility and fruiting body development. One gene, MXAN 3656, was further characterized to determine its role in development and place it on the M. xanthus developmental pathway.

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