RESUMO
Two Pb(II)-resistant bacteria isolated from a soil containing 2,500 mg/kg of Pb were identified by 16S rRNA sequencing analysis as Delftia sp. and designated as 3C and 6C. Both isolates grew at a Pb(II) concentration of 62 mg/L and at the stationary phase showed a Pb(II)-sorption capability of 10 ± 1.5 (3C) and 5 ± 0.8 (6C) mg/g of biomass. Biochemical properties related to heavy metal resistance and plant growth promotion were analyzed and compared with the Cr(VI)-resistant plant growth-promoting Delftia sp. JD2, previously reported by our group. Both isolates and JD2 were resistant to Cr(VI), Pb(II) and many antibiotics, produced siderophores and the phytohormone indole-3-acetic, and showed clover growth-promoting activity in greenhouse conditions. Interestingly, the occurrence of integron class 1 was shown in all isolates. Our results add to previous reports and suggest that bacteria of the genus Delftia could be consider as good candidates for the design of technologies for cleaning up contaminated environments and/or the production of biofertilizers.
Assuntos
Biodegradação Ambiental , Delftia/isolamento & purificação , Delftia/fisiologia , Fertilizantes , Microbiologia do Solo , Antibacterianos/farmacologia , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Delftia/classificação , Delftia/genética , Farmacorresistência Bacteriana , Ácidos Indolacéticos/metabolismo , Chumbo/toxicidade , Dados de Sequência Molecular , Desenvolvimento Vegetal , Reguladores de Crescimento de Plantas/metabolismo , RNA Ribossômico 16S/genética , Análise de Sequência de DNARESUMO
A chromium (Cr)-resistant bacterium isolated from soil containing 6,000 mg/kg of Cr was identified based on 16S rRNA gene sequence analysis as Delftia, and designated as JD2. Growth of JD2 was accompanied with reduction of Cr(VI) to Cr(III) in liquid medium initially containing 100 mg/L Cr(VI), the maximum concentration allowing growth. JD2 showed NADH/NADPH-dependent reductase activity associated with the soluble fraction of cells. The results suggest that JD2 might be a good candidate for the treatment of highly Cr(VI)-contaminated water and/or industrial effluents. The isolate produced indole-3-acetic acid in the presence and absence of Cr(VI) and showed free-living nitrogen-fixing activity possibly attributable to a V-nitrogenase. JD2 did not counteract the harmful effect of Cr(VI) during leguminous plant growth and nodulation by rhizobial strains but functioned as a "helper" bacterium to enhance the performance of rhizobial inoculant strains during inoculation of alfalfa and clover (used as model plants to study plant growth-promoting activity) in the absence of Cr(VI).