Complex quorum-sensing regulatory systems regulate bacterial growth and symbiotic nodulation in Mesorhizobium tianshanen
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SHORT COMMUNICATION
Complex quorum-sensing regulatory systems regulate bacterial growth and symbiotic nodulation in Mesorhizobium tianshanense Huijuan Cao Æ Menghua Yang Æ Huiming Zheng Æ Jiang Zhang Æ Zengtao Zhong Æ Jun Zhu
Received: 14 August 2008 / Revised: 11 December 2008 / Accepted: 16 December 2008 / Published online: 30 December 2008 Ó Springer-Verlag 2008
Abstract LuxR/LuxI-type quorum-sensing systems have been shown to be important for symbiotic interactions between a number of rhizobium species and host legumes. In this study, we found that different isolates of Mesorhizobium tianshanense, a moderately-growing Rhizobium that forms nodules on a number of types of licorice plants, produces several different N-acyl homoserine lactone-like molecules. In M. tianshanense CCBAU060A, we performed a genetic screen and identified a network of regulatory components including a set of LuxI/LuxRfamily regulators as well as a MarR-family regulator that is required for quorum-sensing regulation. Furthermore, compared with the wild-type strains, quorum-sensing deficient mutants showed a reduced growth rate and were defective in nodule formation on their host plant Glycyrrhiza uralensis. These data suggest that different M. tianshanense strains may use diverse quorum-sensing systems to regulate symbiotic process.
H. Cao, M. Yang, and H. Zheng contributed equally to this work. Communicated by E. Stackebrandt. H. Cao M. Yang H. Zheng J. Zhang J. Zhu (&) Department of Microbiology, MOA Key Lab of Microbiological Engineering of Agricultural Environment, Nanjing Agricultural University, Nanjing, China e-mail: [email protected] Z. Zhong The State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing, China
Keywords Mesorhizobium tianshanense Autoinducer synthase MarR-family Nodulation
Introduction It is known that many bacteria produce chemical signaling molecules, called autoinducers, to monitor their own population density and regulate gene expression accordingly. Bacteria use this process, referred as quorum-sensing, to regulate physiological activities such as plasmid transfer, antibiotic production, virulence, symbiotic processes and biofilm formation (Taga and Bassler 2003; Winans and Bassler 2008). Many Gram-negative bacteria utilize LuxI/ LuxR-type quorum-sensing regulatory systems. LuxI-type proteins are responsible for synthesis of N-acyl homoserine lactones (AHLs) quorum signals (Whitehead et al. 2001). Meanwhile, LuxR-type proteins are considered to be the main regulatory components of quorum-sensing systems, and share two regions of sequence conservation, an AHL binding domain and a DNA binding motif (Shadel et al. 1990; Slock et al. 1990). When a threshold level of AHL concentration within the cell is reached, the LuxR-type protein becomes activated by binding the AHL molecule, then binding to specific target gene promoters and regulating transcription (Zhu and Winans 1999; Fuqua and Greenberg 2002; Zhang et al. 2002). N-acyl homoserine lactone signals are found in many
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