Characterization of plant growth promoting rhizobacteria isolated from polluted soils and containing 1-aminocyclopropane-1-carboxylate deaminase

Fifteen bacterial strains containing 1-aminocyclopropane-1-carboxylate (ACC ) deaminase were isolated from the rhizoplane of pea (Pisum sativum L.) and Indian mustard (Brassica juncea L.) grown in different soils and a long-st anding sewage sludge contaminated with heavy metals. The isolated strains w ere characterized and assigned to various genera and species, such as Pseud omonas brassicacearum, Pseudomonas marginalis, Pseudomonas oryzihabitans, P seudomonas putida, Pseudomonas sp., Alcaligenes xylosoxidans, Alcaligenes s p., Variovorax paradoxus, Bacillus pumilus, and Rhodococcus sp. by determin ation of 16S rRNA gene sequences. The root elongation of Indian mustard and rape (Brassica napus var. oleifera L.) germinating seedlings was stimulate d by inoculation with 8 and 13 isolated strains, respectively. The bacteria were tolerant to cadmium toxicity and stimulated root elongation of rape s eedlings in the presence of 300 muM CdCl2 in the nutrient solution. The eff ect of ACC-utilising bacteria on root elongation correlated with the impact of aminoethoxyvinylglycine and silver ions, chemical inhibitors of ethylen e biosynthesis. A significant improvement in the growth of rape caused by i noculation with certain selected strains was also observed in pot experimen ts, when the plants were cultivated in cadmium-supplemented soil. The bioma ss of pea cv. Sparkle and its ethylene sensitive mutant E2 (sym5), in parti cular, was increased through inoculation with certain strains of ACC-utilis ing bacteria in pot experiments in quartz sand culture. The beneficial effe ct of the bacteria on plant growth varied significantly depending on indivi dual bacterial strains, plant genotype, and growth conditions. The results suggest that plant growth promoting rhizobacteria containing ACC deaminase are present in various soils and offer promise as a bacterial inoculum for improvement of plant growth, particularly under unfavourable environmental conditions.