Structural analysis of four strains of Paracoccus denitrificans

Two out of eleven newly isolated strains of Paracoccus denitrificans were investigated by light and electron microscopic methods and compared with two strains of P. denitrificans already kept in culture collections. Samples were taken from different growth phases revealing short rods and nearly spherical cells in the exponential growth phase, and an increasing ratio of nearly spherical cells in the stationary growth phase. Cell division followed the binary fission mode; higher cell aggregates were not observed. Fine structural analysis revealed extracellular surface material stainable with Ruthenium red, a gram-negative cell wall and different storage material inclusions. Structural properties and variations within the four strains under investigation are discussed and compared with those of related bacteria.