Cadmium removal and indole acetic acid production by ureolytic bacteria isolated from rhizosphere soils

This work reports the isolation of 54 ureolytic bacteria with microbiologically induced carbonate precipitation (MICP) activity from Theobroma cacao L. rhizosphere soils with Cd concentration ranging from 0.49 to 21.29 mg kg^{- 1}. Analysis of the 16 S rRNA gene showed the isolates belong to the genera Serratia, Pseudomonas, Comamonas, Klebsiella, Bacillus, Citrobacter, Flavobacterium, Delftia, and Stenotrophomonas. They showed ureolytic activity between 0.31 and 1.01 µmol NH₄⁺ mL^{- 1} h^{- 1} and produced the phytohormone indole acetic acid (IAA). Interestingly, Cd was observed to increase ureolytic activity and did not affect the IAA production of various isolates. Cadmium removal in solution ranged from 4.4 to 87.0% after 48 h. Strains Serratia sp. 89a, Klebsiella sp. 76 h, and Stenotrophomonas sp. 67w exhibited the best performance (> 80%). Cadmium removal through MICP by the genera Delftia, Flavobacterium, and Klebsiella is reported for the first time. Results suggest the isolated bacteria have the potential for Cd bioremediation and could be used to alleviate metal-induced stress through IAA production.