ABSTRACT
Microorganisms play an important role in immobilizing and detoxifying excessive Mn; however, there is so far a lack of sufficient information concerning highly Mn(II)-tolerant bacteria. The present study was conducted to analyze the bio-sorption characteristics of a strain (HM8) isolated from manganese ore wastes. Analytical data from the 16S rDNA sequence determination showed that the species, HM8, had a 99% similarity to Ralstonia pickettii. Results from the designed physiological, biochemical and isothermal adsorption tests indicated that HM8 did not only grow well at a Mn(II) concentration level of 10,000 mg/L but also removed 1,002.83 mg/L of Mn(II) from the bulk solution of the culture, showing that the isolated strain possessed strong capabilities to tolerate and remove Mn(II). In the isothermal bio-sorption experiments performed to investigate the effects of relevant factors on Mn(II) sorption, the highest Mn(II) removal rate was obtained at the contact time 72 h, temperature 40°C, and pH 6.0, while the differences in both strain growth and Mn(II) removal rate between different inoculated HM8 doses were found to be insignificant within the tested range. Scanning electron microscopy showed that, under Mn(II) stress, HM8 cells appeared irregular and cracked, with apparent wrinkles on the surface. The peaks in the Fourier transform infrared spectra showed that hydroxyl and carboxyl groups were the main functional groups for Mn(II) adsorption. The experimental data supported the practical application of HM8 as a biological adsorbent for remediation of heavily Mn contaminated sites.
Subject(s)
Manganese , Ralstonia pickettii/physiology , Biodegradation, Environmental , Environmental Pollutants/metabolism , Hydrogen-Ion Concentration , Manganese/metabolism , Mining , Phylogeny , RNA, Bacterial , RNA, Ribosomal, 16S , Ralstonia pickettii/genetics , Ralstonia pickettii/isolation & purification , Ralstonia pickettii/ultrastructure , Soil Microbiology , Species Specificity , Stress, Physiological , TemperatureABSTRACT
Ralstonia pickettii isolated from copper-contaminated lake sediment are adapted to high levels of copper after 100 years of selective pressure. Two R. pickettii strains (12D and 12J) were selected for the studies reported herein due to their distinct differences in genomic structure, different metal resistance patterns and carriage of a filamentous phage. Copper sequestration studies revealed that these strains could bind up to 27.44 (12D) and 38.19 (12J) mg copper per g dry weight of cells and that viable cells sequestered more copper than heat-killed cells. Viable cells and heat-killed cells had significantly different saturation binding curves, indicating that one or more unique copper sequestration mechanism(s) was involved in binding by viable cells. Electron microscopy showed alteration of cell outer envelope after cells were grown in the presence of copper, suggesting that the accumulation of copper was membrane associated. X-ray Absorption Near Edge Structure and Extended X-ray Absorption Fine Structure revealed that the copper sequestered was present as Cu(II) and bound to oxygen and/or nitrogen. Recent completion of the genome sequence revealed that an approximately 220 kb region was enriched with metal resistance and transporter genes found in multiple copies. Comparative sequence analysis revealed that several genes may have been derived from horizontal transfer. Hence, rapid adaptation of R. pickettii to high concentrations of metal appears due to robust gene duplication and importation of several types of resistance determinants.
