RhizoRegNet combines transcriptome data and operon predictions with published data on regulatory interactions. By allowing searching and visualisation of complex transcriptional regulatory networks, RhizoRegNet advances our understanding of transcriptional regulation in Sinorhizobium meliloti. The current version of RhizoRegNet is divided into 13 functional modules containing information for 114 regulators, 475 regulated genes, and 178 transcription factor binding motifs. Presently, it contains regulatory network information for S. meliloti and the closely related bacterium, S. medicae, but can be expanded to include other rhizobial species.
Jan Baumbach, Alexander Goesmann (Bielefeld University, Germany)
GenoMik-Plus (BMBF), 2006-2010
Opposing regulation of exopolysaccharide biosynthesis and motility in Sinorhizobium
Bacteria that are able to switch between different lifestyles are widely spread. Changing the lifestyle is usually stimulated by alterations in environmental conditions. A frequently observed pattern is the occurrence in a planktonic motile state and as cells attached to surfaces which may involve biofilm formation. Flagellar motility and chemotaxis are characteristic of bacteria growing in suspension in a fluid environment. It allows bacteria to move towards nutrients or other attractants and to escape from stress factors. The production of exopolysaccharides (EPS) is typical for bacteria that are attached to surfaces. EPS are important components of bacterial protection strategies against biotic and abiotic stress factors and crucial elements for cell aggregation, surface attachment and biofilm formation. Both, motility and EPS biosynthesis, contribute to swarming motility and early steps of biofilm formation, but swimming motility and a strong production of EPS probably exclude each other. Since both are high energy-demanding processes, they frequently underlie opposing regulation. EPS biosynthesis and motility are controlled by a regulatory network that couples both processes to global sensory and regulatory modules. In this project, we investigate the network architecture and signaling routes that are responsible for the opposing regulation of EPS production and motility in Sinorhizobium.
Collaborative Research Center SFB 987 (German Research Foundation)
Autosignaling (quorum sensing) in alpha-rhizobia
Intercellular communication by means of small signal molecules synchronizes gene expression and coordinates functions among bacteria. This population density-dependent regulation is known as quorum sensing. Quorum sensing is frequently mediated by acyl homoserine lactone (AHL) autoinducers. Sinorhizobium meliloti possesses an AHL-based quorum sensing system controlling functions that are important for adaptation, competition and establishment of symbiosis. We investigate the molecular mechanisms, biological role, and regulation of quorum sensing in S. meliloti and related alpha-rhizobia.
Dario Anselmetti (Bielefeld University), Peter Pfaffelhuber (University of Freiburg, Germany), Norbert Sewald (Bielefeld University, Germany)
FRISYS (BMBF), 2008-2010
SFB613 (German Research Foundation), 2002-2008
Molecular mechanisms and benefits of phenotypic heterogeneity in Sinorhizobium meliloti populations
The nitrogen-fixing symbiotic alpha-proteobacterium S. meliloti produces exopolysaccharides (EPS) as a common good. Heterogeneity in EPS production has been observed, where a sub-population heavily engages in EPS production while other individuals vary from intermediate to absent production. Explanations for heterogeneity, both its biological significance and its molecular mechanisms are the focus of this interdisciplinary project involving experimentation and modeling approaches. We particularly investigate the role of quorum sensing in phenotypic heterogeneity of the isogenic population. Furthermore, we are interested in properties of regulatory gene circuits that lead to heterogeneity in isogenic bacterial populations.
Peter Pfaffelhuber (University of Freiburg, Germany)
Priority Program SPP 1617 (German Research Foundation)
Regulation of the cell cycle in bacteria is less elucidated than in eukaryotes, mostly due to the small size of the bacterial cells which makes it difficult to gain insight into the subcellular processes like bacterial chromosome segregation or septum formation. Bacterial cell division is a highly organized process, precisely coordinated in space and time.
Proteins involved in cell division and its regulation display different sub-cellular localization patterns that change over the course of the cell cycle. Expression of the regulatory genes is actively controlled not only at the stage of transcription, but also post-translationally, by trafficking, phosphorylation and proteolysis.
In indeterminate nodules, induced by Sinorhizobium meliloti on its host plants, deregulation of the cell cycle takes place. Here, bacteria, as well as the infected plant cells become enlarged and polyploid through several cycles of endoreduplication of the genome uncoupled from cell division. We investigate the control of the S. meliloti cell cycle and the mechanisms of deregulation during symbiotic differentiation.
SYNMIKRO (LOEWE program,State of Hesse)