Three newly isolated plant growth-promoting bacilli facilitate the seedling growth of canola, Brassica campestris

Three strains of plant growth-promoting bacteria were isolated from southeastern Wisconsin soils, based upon the ability to utilize the compound 1-aminocyclopropane-1-carboxylic acid (ACC) as a sole nitrogen source. These novel bacteria have been identified as Bacillus circulans DUC1, Bacillus firmus DUC2, and Bacillus globisporus DUC3. Each strain displayed similar levels of ACC deaminase activity (EC 4.1.99.4) and stimulated root elongation in canola (Brassica campestris) seedlings under gnotobiotic conditions. Soil inoculations with respective bacterial strains increased the root and shoot lengths and fresh and dry weights of potted canola plants. Similarly, a soil inoculation with B. globisporus DUC3 promoted root and shoot growth of plants subjected to a diurnal temperature regime. This is the first report of plant growth-promoting bacilli with the ability to catabolize ACC.