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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. [ABSTRACT FROM AUTHOR]

Combining phytoremediation plants and microorganisms is a promising method of remediating heavy metal contaminated soil. In this study, two manganese-tolerant strains were isolated from Mn slag and identified as Bacillus cereus HM5 and Bacillus thuringiensis HM7. These two Bacillus spp. have the ability to dissolve phosphorus, produce IAA and iron carrier. A pot experiment of Broussonetia papyrifera was conducted to explore potential of B. cereus HM5 and B. thuringiensis HM7 to improve effect of remedying Mn pollution by B. papyrifera. The strains were inoculated under different Mn treated (5 mmol/L, 50 mmol/L, Mn slag) respectively and the growth, root structure, root activity, physiological and biochemical characteristics of the leaves and accumulation of Mn for B. papyrifera were determinated. The effects of the soil environment to remediation were observed, the results showed that the biomass, total root length, surface area, crossings, tips, forks and root activity of B. papyrifera with inoculated strain were higher than those of the control group. The inoculation of these two Bacillus spp. increased the absorption of Mn by B. papyrifera and the concentration of Mn in the aerial parts of plants, indicating that the two strains could promote the growth of B. papyrifera and the accumulation of Mn. In addition, microbes reduced malonaldehyde content and the activities of antioxidant enzymes in leaves, suggesting that the two Bacillus spp. reduced Mn-induced oxidative stress. The principal component analysis showed that the added Bacillus strain prefer to promote plant root function maintenance and improve soil environment, rather than direct adsorption of heavy metals. These observations indicated that B. cereus HM5 and B. thuringiensis HM7 were valuable microorganisms, which could improve the remediating efficiency of B. papyrifera under Mn-contaminated soil. • B. cereus HM5/ B. thuringiensis HM7 improved the accumulation of Mn by B. papyrifera. • B. cereus HM5 and B. thuringiensis HM7 could reduce oxidative stress induced by Mn. • The strains promoted the growth of plant root system and improved soil environment. [ABSTRACT FROM AUTHOR]

Our study navigated investigated the metal adsorption ability of bacterial Bacillus cereus strain HM-5 isolated from manganese ore. The effects of pH, initial metal ions concentration, biomass dose, contact time, and temperature on biosorption were studied. The results showed that the biosorption capacity of the B. cereus strain HM-5 for the metallic ions reached up to 98.9% for Mn at 600 mg/L initial metal ion concentration. The biosorptoin was most affected by pH and incubation temperature. Optimal pH and temperature were 6 and 35°C, respectively. Optimal contact time was 5 d for biosorption by B. cereus strain HM-5. The surface chemical functional groups of B. cereus biomass identified by Fourier transform infrared (FTIR) were hydroxyl, alkyl, amide, phosphoryl, and phosphoric acid groups, which may be involved in the biosorption of heavy metals. SEM micrographs indicated that B. cereus HM-5 cells were irregular and cracked with the appearance of wrinkles and many flocs on the surface after Mn stress. The results showed that the selected bacteria had good application prospect in manganese-contaminated soil remediation. [ABSTRACT FROM AUTHOR]