Specificity of root colonization by symplasmata-forming Pantoea agglomerans

Abstract

The mode of rice, wheat, and maize root colonization by enterobacterial nitrogen-fixing bacteria (Pantoea agglomerans NO30, Rahnella aquatilis TRO1, and R. aquatilis 339) was studied by electron microscopy. The maize isolate TRO1 abundantly colonized maize. Only a few TRO1 bacteria were observed on rice roots. Adhesion of TRO1 to wheat roots was mediated by fimbriae. TRO1 could produce exopolymers of wheat root surfaces. The wheat isolate, strain 339, colonized plant roots to a lesser extent. No fimbriae or exopolymers were observed. Pantoea agglomerans strain NO30, isolated from rice, formed cell aggregates called symplasmata in nutrient broth at the start of the exponential growth phase. Strain NO30 was only detected as individual cells on wheat roots. Rice roots were colonized mainly by symplasmata.