title: Cadmium-tolerant bacteria reduce the uptake of cadmium in rice: potential for microbial bioremediation.
abstract: We selected 24 bacterial isolates that could tolerate up to 2500 µM CdCl2 from the soil of rice fields downstream from a zinc-mineralized area contaminated with a high level of cadmium (Cd). In the presence of 500 µM CdCl2, all isolates grew slower and with a prolonged lag-phase compared to in the absence of Cd. Cd-binding capacity was high and ranged from 6.38 to 9.38 log[Cd(atom)]/cell. The stability of Cd complexes in bacteria was affected by 1mM EDTA. In 500 µM CdCl2, all isolates produced 0.7 to 4.8-fold more inorganic sulfide and 0.6 to 2.2-fold more thio-rich compounds containing SH groups. Out of 24 Cd-tolerant bacterial isolates, KKU2500-3, -8, -9 and -20 were able to promote the growth of Thai jasmine rice (Kao Hom Mali 105) seedlings in the presence of 200 µM CdCl2, and KKU2500-3 produced the highest numbers of fibrous root. Interestingly, these 4 isolates increased Cd tolerance and decreased the accumulation of Cd in rice by 61, 9, 6, and 17% when grown in the presence of 200 µM CdCl2. Of the 4 isolates, KKU2500-3 produced more inorganic sulfide when grown in CdCl2 at 500-2000 µM. XANES analyses indicated that this isolate precipitated a detectable amount of cadmium sulfide (CdS) when grown in 500 µM CdCl2. Thus, the isolate KKU2500-3 could possibly transform toxic, soluble CdCl2 into non-toxic, insoluble CdS. These 4Cd-tolerant bacterial isolates were identified via 16S rDNA sequencing and classified as Cupriavidus taiwanensis KKU2500-3 and Pseudomonas aeruginosa KKU2500-8, -9, and -20.
authors.affiliation: Department of Microbiology, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand. surasak@kku.ac.th
authors.forename: Surasak
authors.initials: S
authors.lastname: Siripornadulsil
authors.forename: Wilailak
authors.initials: W
authors.lastname: Siripornadulsil
mesh_terms: D000222:Adaptation, Physiological; D001419:Bacteria / Q000378:metabolism; D001673:Biodegradation, Environmental; D002104:Cadmium / Q000378:metabolism / Q000633:toxicity*; D012275:Oryza / Q000378:metabolism* / Q000382:microbiology / Q000502:physiology; D018517:Plant Roots / Q000737:chemistry / Q000382:microbiology; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000378:metabolism / Q000633:toxicity*
chemical_list: D012987:Soil; D012989:Soil Pollutants; D002104:Cadmium