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Title: CYCLIC B-GLUCAN SYNTHESIS IN BRADYRHIZOBIUM

Author
item GROSS, KENNETH
item KEISTER, DONALD
item BHAGWAT, ARVIND - UNIVERSITY OF MARYLAND

Submitted to: Proceedings of European Nitrogen Fixation Conference
Publication Type: Abstract Only
Publication Acceptance Date: 3/13/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Bradyrhizobium japonicum synthesizes periplasmic cyclic B-(1,3);B-(1,6)-D- glucans during growth in hypoosmotic environments and evidence is growing that these molecules may have a specific function during plant-microbe interactions in additions to osmoregulation. Site-directed Tn5 mutagenesis of the DNA region upsteam of the ndvB locus resulted in identification of a anew gene (ndvC) involved in B-(1,3);B-(1,6)-glucan synthesis and in nodule development. The predicted translation product was a membrane polypeptide (ca. 62 KDa). It contained a conserved sequence characteristic of a nucleoside-sugar binding motif and had 51% similarity with B-glucanosyl transferase from Candida albicans. B. japonicum carrying a Tn5 insertion in ndvC resulted in synthesis of altered cyclic B-glucans composed almost entirely of B-(1,3)-glycosyl linkages. The mutant strain was only slightly sensitive to hypoosmotic growth conditions as compared with the ndvB mutant but it was severely impaired in symbiotic interactions with soybean (Glycine max). Nudulation was delayed by several days and many small nodule-like structure were formed which were devoid of infection threads or viable bacteria. This new class of glucan molecules appears to function as osmolytes but not in supporting symbiotic effectiveness. Thus segregation of the pleiotropic phenotypes due to mutations in the glucan systhesis locus was observed for the first time. These results suggest that the structure of the B-glucan molecule is important for a successful symbotic interactions, and that B- glucans may have a specific function in addition to their role in hypoosmotic adaptation.