PRODUCTION OF CELL-ASSOCIATED POLYSACCHARIDES OF RHIZOBIUM-FREDII USDA205 IS MODULATED BY APIGENIN AND HOST ROOT EXTRACT

Rhizobium fredii USDA205 cells were cultured in the presence of 4',5,7 -trihydroxyflavone (apigenin), a compound that has been shown to induc e the nod genes and other symbiosis-related genes in R. fredii. The ce ll-associated polysaccharides were then extracted with hot phenol/wate r, separated by repetitive gel filtration chromatography, and analyzed by polyacrylamide gel electrophoresis, nuclear magnetic resonance spe ctrometry, highperformance anion-exchange chromatography, and gas chro matography. These analyses showed that apigenin effects a modulation i n the production of some cell-associated bacterial polysaccharides: 1) The production of a glucan is severely attenuated; 2) the lipopolysac charide O antigen is modified in composition and M(r) distribution; an d 3) the ratio of two extracted polysaccharides, which are structurall y analogous to group II K antigens (capsular polysaccharides), is alte red. Similar effects resulted from the inclusion of host plant root ex tract in the growth medium.