Peat Culture of Rhizobium trifolii: an Examination by Electron Microscopy

Abstract

SummaryPeat cultures of Rhizobium trifolii strain TA1 were examined by electron microscopy of thin sections of aldehyde‐OsO4 fixed Araldite embedded particles, and scanning reflection electron microscopy of the peat particle surfaces. The Badenoch peat used showed plant cell wall fragments; membranes with dense‐light‐dense appearance in vesicular or linear form; tubular structures; other unidentified wall‐like fragments, all usually surrounded by a matrix of varying electron density and granularity. The general level of electron density was high, even in plant wall fragments, although some electron‐transparent spaces were present in the matrix. Remains of bacteria and actinomycetes were often found within the peat particles. Particle shape varied a great deal; the surface was irregular with many crevices. Rhizobium cells were found on the surfaces, and sometimes in crevices of the particles. Rarely > 10 cells were found together and the cells were usually several μm apart. The rhizobia were structurally similar to broth cultured log phase cells, but often the region between cell wall membrane and plasma membrane was very electron dense. The rhizobia were usually enmeshed in a fibrillar matrix connecting them to the peat particles; this was probably the film seen to cover the bacteria in scanning surface pictures.