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A putative 3‐hydroxyisobutyryl‐CoA hydrolase is required for efficient symbiotic nitrogen fixation in Sinorhizobium meliloti and Sinorhizobium fredii NGR234
Author(s) -
Zamani Maryam,
diCenzo George C.,
Milunovic Branislava,
Finan Turlough M.
Publication year - 2017
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/1462-2920.13570
Subject(s) - biology , sinorhizobium meliloti , nitrogen fixation , nitrogenase , catabolism , sinorhizobium , rhizobia , symbiosis , biochemistry , mutant , gene , rhizobiaceae , microbiology and biotechnology , metabolism , genetics , bacteria
Summary We report that the smb20752 gene of the alfalfa symbiont Sinorhizobium meliloti is a novel symbiotic gene required for full N 2 ‐fixation. Deletion of smb20752 resulted in lower nitrogenase activity and smaller nodules without impacting overall nodule morphology. Orthologs of smb20752 were present in all alpha and beta rhizobia, including the ngr_b20860 gene of Sinorhizobium fredii NGR234. A ngr_b20860 mutant formed Fix − determinate nodules that developed normally to a late stage of the symbiosis on the host plants Macroptilium atropurpureum and Vigna unguiculata . However an early symbiotic defect was evident during symbiosis with Leucaena leucocephala , producing Fix − indeterminate nodules. The smb20752 and ngr_b20860 genes encode putative 3‐hydroxyisobutyryl‐CoA (HIB‐CoA) hydrolases. HIB‐CoA hydrolases are required for l ‐valine catabolism and appear to prevent the accumulation of toxic metabolic intermediates, particularly methacrylyl‐CoA. Evidence presented here and elsewhere (Curson et al ., [Curson, A.R.J., 2014], PLoS ONE 9:e97660) demonstrated that Smb20752 and NGR_b20860 can also prevent metabolic toxicity, are required for l ‐valine metabolism, and play an undefined role in 3‐hydroxybutyrate catabolism. We present evidence that the symbiotic defect of the HIB‐CoA hydrolase mutants is independent of the inability to catabolize l ‐valine and suggest it relates to the toxicity resulting from metabolism of other compounds possibly related to 3‐hydroxybutyric acid.