An Accessory Factor for Legume Nodule Bacteria

Abstract

Certain spp. of legume-nodule bacteria require an accessory fac-tor for growth. Rhizobium trifolii was studied chiefly, but R. leguminosarum, R. meliloti, and R. phaseoli behaved similarly. The necessary factor, previously designated as "coenzyme R," is a respiration coenzyme, essential primarily for respiration and indirectly for growth. It is widely distributed in plant materials and probably also in animal products. Yeast, cane molasses, natural humic acid, and commercial egg albumen contain relatively high concentrations. The accessory factor was prepared in fairly concentrated form by extracting either commercial sucrose or cane molasses with absolute alcohol, followed by removal of the solvent and taking up of the residue in water. Addition of 16-20 p.p.m. dry matter of such an extract, still containing 75% sugar, produced a half maximum growth. Direct comparisons of growth in the commonly used sugar-mineral-yeast medium with that in a sugar-mineral-nitrate-coenzyme medium showed growth in the latter to be usually 60-90% as good as in the former, even though yeast contains many additional substances known to favor growth, particularly N and traces of various minerals in readily available form.