An apigenin-induced decrease in K-antigen production by Sinorhizobium sp. NGR234 is y4gM- and nodD1-dependent

Cultured cells of Sinorhizobium sp. NGR234 produce an abundance of capsular polysaccharides, or K antigens; however, cells that are cultured in the presence of apigenin, a nod gene inducer, exhibited a significant reduction in K-antigen production. The flavonoid-induced modulation in capsule production appeared to be related to the phase-shift changes associated with bacteroid differentiation. Therefore, the polysaccharides were extracted from Sinorhizobium sp. NGR234 bacteroids recovered from Vigna unguiculata cv Red Caloona root nodules, and subsequent analyses showed that the bacteroid extracts were virtually devoid of K-antigen. Polysaccharide extracts from two nodulation mutants cultured in the presence of apigenin were then analyzed, and the results showed that the flavonoid-inducible decrease in K-antigen production is y4gM- and nodD1-dependent.

Graphical abstractSinorhizobium sp. NGR234 is a broad host-range microsymbiont, and its cells cultured in the presence of apigenin exhibit a reduction in K-antigen (densely charged, acidic polysaccharide) production, but y4gM and nodD1 mutants do not. Thus, phase-shift attenuation of K-antigen production is flavonoid-inducible, and y4gM- and nodD1-dependent.Figure optionsDownload full-size imageDownload as PowerPoint slide