Manganese transport is essential for N 2 ‐fixation by Rhizobium leguminosarum in bacteroids from galegoid but not phaseoloid nodules

Abstract

Summary Rhizobium leguminosarum has two high‐affinity Mn 2+ transport systems encoded by sitABCD and mntH . In symbiosis, sitABCD and mntH were expressed throughout nodules and also strongly induced in Mn 2+ ‐limited cultures of free‐living cells. Growth of a sitA mntH double mutant was severely reduced under Mn 2+ limitation and sitA and mntH single mutants were more sensitive to oxidative stress. The double sitA mntH mutant of R. leguminosarum was unable to fix nitrogen (Fix ‐ ) with legumes belonging to the galegoid clade ( Pisum sativum , Vicia faba and Vicia hirsuta ). The presence of infection thread‐like structures and sparsely‐packed plant cells in nodules suggest that bacteroid development was blocked, either at a late stage of infection thread progression or during bacteroid‐release. In contrast, a double sitA mntH mutant was Fix + on common bean ( Phaseoli vulgaris ), a member of the phaseoloid clade of legumes, indicating a host‐specific symbiotic requirement for Mn 2+ transport.

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