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Critical protective role of bacterial superoxide dismutase in Rhizobium –legume symbiosis
Author(s) -
Santos Renata,
Hérouart Didier,
Puppo Alain,
Touati Danièle
Publication year - 2000
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2000.02178.x
Subject(s) - rhizobia , biology , superoxide dismutase , rhizobium , symbiosis , sinorhizobium meliloti , nitrogen fixation , reactive oxygen species , nitrogenase , bacteria , legume , root nodule , mutant , microbiology and biotechnology , rhizobiaceae , oxidative stress , biochemistry , botany , gene , genetics
In nitrogen‐poor soils, rhizobia elicit nodule formation on legume roots, within which they differentiate into bacteroids that fix atmospheric nitrogen. Protection against reactive oxygen species (ROS) was anticipated to play an important role in Rhizobium –legume symbiosis because nitrogenase is extremely oxygen sensitive. We deleted the sodA gene encoding the sole cytoplasmic superoxide dismutase (SOD) of Sinorhizobium meliloti . The resulting mutant, deficient in superoxide dismutase, grew almost normally and was only moderately sensitive to oxidative stress when free living. In contrast, its symbiotic properties in alfalfa were drastically affected. Nitrogen‐fixing ability was severely impaired. More strikingly, most SOD‐deficient bacteria did not reach the differentiation stage of nitrogen‐fixing bacteroids. The SOD‐deficient mutant nodulated poorly and displayed abnormal infection. After release into plant cells, a large number of bacteria failed to differentiate into bacteroids and rapidly underwent senescence. Thus, bacterial SOD plays a key protective role in the symbiotic process.