An order containing easily stained rod-shaped or spherical bacteria with, in the motile forms, numerous flagella (see peritrichous
). The rod-shaped organisms are assigned to the following families: Azotobacteraceae (which contains free-living nitrogen-fixing soil bacteria, e.g. Azotobacter), Achromobacteraceae, Rhizobiaceae which contains symbiotic nitrogen fixers, e.g. Rhizobium, and some gall-forming bacteria, e.g. Agrobacterium), Enterobacteriaceae (which contains some plant parasites, e.g. Erwinia), Brucellaceae, and Bacteroidaceae. All these families are gram-negative. Grampositive rods are assigned to the families Brevibacteriaceae, Lactobacillaceae (see lactic acid bacteria
), Propionibacteriaceae, Corynebacteriaceae (containing Corynebacterium, which causes certain plant rots), and Bacillaceae. The spherical organisms are divided into the gram-negative Neisseriaceae and the gram-positive Micrococcaceae.