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The Type IV Secretion System of Sinorhizobium meliloti Strain 1021 Is Required for Conjugation but Not for Intracellular Symbiosis

Kathryn M. Jones, Javier Lloret, Joseph R. Daniele, and Graham C. Walker^*

Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139

Received 21 January 2006/ Accepted 28 November 2006

The type IV secretion system (T4SS) of the plant intracellular symbiont Sinorhizobium meliloti 1021 is required for conjugal transfer of DNA. However, it is not required for host invasion and persistence, unlike the T4SSs of closely related mammalian intracellular pathogens. A comparison of the requirement for a bacterial T4SS in plant versus animal host invasion suggests an important difference in the intracellular niches occupied by these bacteria.

Published ahead of print on 8 December 2006.

Present address: Departamento de Biologia, Universidad Autonoma de Madrid, Madrid, Spain.

Present address: Graduate School of Arts and Sciences, Harvard Medical School, Boston, MA.