Title

Nla4 and Nla18, key regulatory proteins required for normal growth and development of Myxococcus xanthus

Date of Award

12-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Anthony G. Garza

Keywords

Myxococcus xanthus, Nla4, Nla18, Regulatory proteins

Subject Categories

Microbiology

Abstract

Changes in gene expression are important for the landmark morphological events that occur during M. xanthus fruiting body development. NtrC-like activators play a prominent role in the coordinated expression of developmental genes. Mutations in the ntrC -like activator genes nla4 and nla18 are known to affect the timing of fruiting body formation, the morphology of mature fruiting bodies, and the sporulation efficiency. In this study we show that early developmental gene expression is altered in the early stages of fruiting body development in nla4 and nla18 cells. Production of A-signal, a quorum-sensing signal required early in development, is severely affected. The earliest event in development, accumulation of the intracellular starvation signal ppGpp is reduced. Thus, there is an early and strong modification of the developmental program in nla4 and nla18 cells.

Further studies revealed that nla4 cells fail to express normal levels of genes whose products are implicated in the regulation of ppGpp accumulation. Inactivation of nla4 reduces GTP accumulation, a precursor of (p)ppGpp, which also stimulates growth related processes in other bacteria. Furthermore, nla4 inactivation causes a dramatic decrease in the M. xanthus vegetative growth rate. It is likely that Nla4 is an important key in modulating (p)ppGpp accumulation by activating the expression of the stringent response related genes during the M. xanthus life cycle.

This study shows that inactivation of nla18 produces a strong defect in M. xanthus vegetative growth. DNA microarray analysis revealed that the vegetative expression patterns of more than 700 genes are altered in nla18 cells. Among the largest classes of altered genes are those which code for putative membrane and membrane-associated proteins. Our findings show that the membrane protein profiles isolated from vegetative nla18 and wild-type cells are noticeably different. Inactivation of nla18 causes misexpression of many genes that are likely to be important for protein synthesis. It therefore appears that nla18 cells are unable to regulate genes that encode important components of the translational machinery, thereby affecting stringent response. Our data are consistent with a model in which Nla18 controls vegetative growth and development by regulating the expression of genes involved in protein synthesis and membrane structure.

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