Novel regulators controlling bacterial survival under stress

50000403v1613
Promoter: Jan Michiels


Description: Transition from fast-growing to non-growing conditions is pivotal in the life cycle of bacteria and essential for successful adaptation to diverse environments. In the life cycle of rhizobia, nitrogen-fixing bacteria that elicit nodules on the roots of their leguminous host plants, these transitions are also crucial for adaptation to the host and survival in the soil. Inside the root nodules, the bacteria differentiate into non-growing bacteroids that convert atmospheric nitrogen into ammonia. Our global view on the way gene expression affects the differentiation process and the maintenance of the bacteroid state is still far from complete. Moreover, little is known about factors contributing to survival of rhizobia in free-living conditions.
Previously, we showed the rel gene of Rhizobium etli to be crucial for the bacterium’s adaptation to symbiotic and free-living non-growing conditions. To identify target genes of R. etli rel and, in general, mechanisms and genes that regulate the adaptation to non-growing conditions, a R. etli transcriptomics analysis was recently carried out within the CMPG-SPI group using tiling microarrays. In this research proposal, we intend to elucidate the role of several regulators, identified based on our tiling array data, in the survival of the bacteria under free-living and symbiotic conditions. We will carry out a detailed phenotypical analysis of the regulatory mutants, complemented with a target analysis of a single regulator, to be selected during the course of this project. In this way, we will lay the foundation for a better understanding of the physiology of growing and non-growing states and factors determining the transitions between them.
The regulators that were selected based belong to five different classes: transcriptional regulators, sigma factors, proteins involved in posttranslational modifications and proteins related to the production of a secondary messenger, c-di-GMP. Furthermore, a gene was selected that encodes a small non-coding RNA. Preliminary experiments show that mutation of at least two of these regulators leads to a strong decrease in symbiotic nitrogen fixation, decreased survival in the stationary phase and/or increased sensitivity to envelope stress, lending support to the approach proposed here.
Combining the various types of data generated in the experiments will allow 1/ the construction of a model for R. etli in which the selected regulator is linked to its target genes and associated phenotypes with regard to survival in the non-growing state ex planta; 2/ linking these data to symbiotic indicators, which will pinpoint survival processes of the intracellular bacteroids inside the plant cell; 3/ extrapolation of the model or parts thereof to other á-proteobacteria, provided that the key elements are conserved.

Reference publications

Braeken, K., M. Fauvart, M. Vercruysse, S. Beullens, I. Lambrichts, and J. Michiels. 2008. Pleiotropic effects of a rel mutation on stress survival of Rhizobium etli CNPAF512. BMC Microbiol 8:219.
Braeken, K., M. Moris, R. Daniels, J. Vanderleyden, and J. Michiels. 2006. New horizons for (p)ppGpp in bacterial and plant physiology. Trends Microbiol 14:45-54.
Moris, M., K. Braeken, E. Schoeters, C. Verreth, S. Beullens, J. Vanderleyden, and J. Michiels. 2005. Effective symbiosis between Rhizobium etli and Phaseolus vulgaris requires the alarmone ppGpp. J Bacteriol 187:5460-9.





Key words: molecular microbiology - biotechnology - nitrogen fixation

Latest application date: 2009-12-31

Financing: Erasmus Mundus External Cooperation Window

Type of Position: scholarship

Duration of the Project : 4 years


Research group: Department of Microbial and Molecular Systems (M#S)

Remarks: 3 years are funded by EMECW, 1 year by other sources