1Department of General Microbiology, M. Curie-Sklodowska University, Akademicka 19, 20-033 Lublin, Poland; 2Department of Botany, Faculty of Agriculture, Warsaw Agricultural University, Rakowiecka 26/30, 02-528 Warsaw, Poland
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Accepted 15 July 1998.
We have identified the three genes pssCDE in Rhizobium leguminosarum bv. trifolii TA1. Even though they were almost identical to earlier identified pssCDE genes of R. leguminosarum, they differed in gene lengths and gene overlaps. The predicted gene products of pssCDE genes shared significant homology to prokaryotic glycosyl transferases involved in exopolysaccharide synthesis. The Tn5 insertion in pssD created the nonmucoid mutant that induced non-nitrogen-fixing nodules. The microscopic analysis of the nodules, induced on Trifolium pratense by the pssD133 mutant, showed abnormally enlarged infection threads densely packed with bacteria, which were released from the infection threads in an unusual way. The symbiosomes were observed very rarely and the nodule remained almost empty. Symbiotic phenotype of the pssD133 suggested a correlation between this mutation and defective endocytosis of bacteria into nodule cells.
© 1998 The American Phytopathological Society