The Effect of Mutations in Glycanase Genes on the Formation of Exo-oligosacharides in Nodule Bacteria Rhizobium leguminosarum bv. viciae VF39

In order to identify the mechanisms underlying the formation of low-molecular-weight forms of acidic exopolysaccharide in the symbiotic bacteria Rhizobium leguminosarum bv. viciae, a comparative analysis of exo-oligosaccharide production was conducted in the wild-type strain and its derivatives with mutations in one (plyB), two (plyBC, pssWplyB), and three (pssWplyBC) glycanase genes. Based on viscometry data and quantitative analysis of polysaccharides, it was concluded that the mutants synthesized an exopolysaccharide with a higher degree of polymerization of repeating octasaccharide units compared to that in the wild-type strain. It was shown that knockout of glycanase genes led to a decrease in the amount of acidic oligosaccharides in the culture medium. It was established that the efficiency of polysaccharide depolymerization by extracellular polysaccharide lyases PlyBC depends on the presence of a functionally active periplasmic glycoside hydrolase PssW. Based on the results of mass spectrometric analysis of exo-oligosaccharides, a scheme for the location of polysaccharide cleavage sites by glycanases was proposed. It was shown that effectiveness of symbiosis with garden pea was reduced in the mutant strains plyBC and pssWplyBC.