The symbiotic relationship between the nitrogen-fixing Sinorhizobium meliloti and its legume host (Medicago sativa) is the result of an intricate signaling network between the host and the symbiont. Quorum sensing, a process that involves the cell density-dependent regulation of gene expression, has been shown to be an integral part of this complex association. It is increasingly clear that many important bacterial activities essential for the effective colonization and pathogenesis of animal or plant hosts are regulated in a population density-dependent manner. This process involves the release and detection of small extra-cellular signal molecules termed autoinducers. The best characterized of these autoinducers are acylated homoserine lactones (AHLs), mostly found in Gram-negative organisms. The overall goal of this research is to determine the role that quorum-sensing plays in the well-characterized relationship between S. meliloti and its host. As a result of our recent work, this symbiotic association is rapidly becoming a paradigm for the study of quorum sensing. S. meliloti possesses a complex series of linked quorum-sensing systems. We have characterized three of those systems (Mel, Sin and Tra) and established that they play a part in nodulation, exopolysaccharide production and conjugal plasmid transfer. The Sin system produces the longest AHLs detected to date. Our work has determined that one of these long-chain AHLs plays a key role in regulating the production of the symbiotically important exopolysaccharide II. Finally, the Sin quorum-sensing system affects the timing and number of nodules it induces on its plant host.
The first aim of this proposal is to determine how the multiple quorum-sensing systems of S. meliloti are regulated and coordinated. Second, we will investigate how the highly hydrophobic AHLs produced by the Sin system are transported across biological membranes. Third, this project seeks to identify the genes controlled by the Sin quorum sensing system and determine their function in the S. meliloti/alfalfa symbiosis. This study will provide a better understanding of the symbiotic/pathogenic relationships between prokaryotes and their eukaryotic hosts and might provide tools for the control and manipulation of such relationships. ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
3R01GM069925-01A2S1
Application #
7189501
Study Section
Prokaryotic Cell and Molecular Biology Study Section (PCMB)
Program Officer
Anderson, James J
Project Start
2005-07-01
Project End
2010-06-30
Budget Start
2005-07-01
Budget End
2006-06-30
Support Year
1
Fiscal Year
2006
Total Cost
$31,238
Indirect Cost
Name
University of Texas-Dallas
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
800188161
City
Richardson
State
TX
Country
United States
Zip Code
75080
Geddes, Barney A; González, Juan E; Oresnik, Ivan J (2014) Exopolysaccharide production in response to medium acidification is correlated with an increase in competition for nodule occupancy. Mol Plant Microbe Interact 27:1307-17
Mueller, Konrad; Gonzalez, Juan E (2011) Complex regulation of symbiotic functions is coordinated by MucR and quorum sensing in Sinorhizobium meliloti. J Bacteriol 193:485-96
Patankar, Arati V; Gonzalez, Juan E (2009) An orphan LuxR homolog of Sinorhizobium meliloti affects stress adaptation and competition for nodulation. Appl Environ Microbiol 75:946-55
Rinaudi, Luciana V; González, Juan E (2009) The low-molecular-weight fraction of exopolysaccharide II from Sinorhizobium meliloti is a crucial determinant of biofilm formation. J Bacteriol 191:7216-24
Gurich, Nataliya; Gonzalez, Juan E (2009) Role of quorum sensing in Sinorhizobium meliloti-Alfalfa symbiosis. J Bacteriol 191:4372-82
Morris, Jennifer; Gonzalez, Juan E (2009) The novel genes emmABC are associated with exopolysaccharide production, motility, stress adaptation, and symbiosis in Sinorhizobium meliloti. J Bacteriol 191:5890-900
Patankar, Arati V; Gonzalez, Juan E (2009) Orphan LuxR regulators of quorum sensing. FEMS Microbiol Rev 33:739-56
Hoang, Hanh H; Gurich, Nataliya; Gonzalez, Juan E (2008) Regulation of motility by the ExpR/Sin quorum-sensing system in Sinorhizobium meliloti. J Bacteriol 190:861-71
Chowdhary, Puneet K; Keshavan, Neela; Nguyen, Hien Q et al. (2007) Bacillus megaterium CYP102A1 oxidation of acyl homoserine lactones and acyl homoserines. Biochemistry 46:14429-37
Glenn, Sarah A; Gurich, Nataliya; Feeney, Morgan A et al. (2007) The ExpR/Sin quorum-sensing system controls succinoglycan production in Sinorhizobium meliloti. J Bacteriol 189:7077-88

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