Studies of bacterial homeostasis Sinorhizobium meliloti and Escherichia coli

The symbiosis between Sinorhizobium meliloti and its plant host Medicago sativa, offers a tractable model to explore the bacterial requirements for endocytic survival in a eukaryotic host. It has been shown that during development of this symbiosis, M. sativa releases an oxidative burst that S. meliloti must be able to overcome in order for symbiotic development to continue. Employing a novel two-part screen, I identified Sinorhizobium meliloti mutants that were both sensitive to oxidative stress and symbiotically defective on the host plant Medicago sativa. The mutants affect a wide variety of cellular processes and represent both novel and previously identified genes important in symbiosis. One mutant I identified was disrupted in sitA, which encodes the periplasmic binding protein of the putative iron/manganese ABC transporter SitABCD. Disruption of sitA causes elevated sensitivity to the reactive oxygen species hydrogen peroxide and superoxide. Disruption of sitA leads to elevated catalase activity and a severe decrease in superoxide dismutase B (SodB) activity and protein level. The decrease in SodB level strongly correlates with the superoxide sensitivity of the sitA mutant. I demonstrate that all free-living phenotypes of the sitA mutant can be rescued by the addition of exogenous manganese but not iron, a result that strongly implies SitABCD plays an important role in manganese uptake in S. meliloti. A second mutant I identified in my screen was disrupted in a previously unexplored orf, SMc0lll3. SMc0lll3 produces anl8 kD protein that is a member of a highly conserved family, universal among bacteria. In addition to being required for S. meliloti symbiosis with alfalfa, SMc01113 is also required to protect the bacterium from a wide range of environmental stresses.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Biology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Davies, Bryan William

Advisor dc:contributor.advisor

• Graham C. Walker.

• Biology.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/43788

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/43788