| As the most reactive inorganic component and products of soil evolution and substance cycling in soils, manganese oxides participate in a wide range of reactions regarding processes of material formation and transformation. Thus they are believed to be one of the major drivers influencing the biogeochemical cycling and the bioavailability of many elements and organic compounds. Increasing evidences have shown that Mn oxide formation in soils is a microbially-mediated process. The Mn(Ⅱ)-oxidizing microorganisms, commonly studied in the biogenic Mn oxide formation, mainly isolated from oceans and were used in free status. However, the soil environment is heterogeneous and more complicated than oceans, so the living condition of bacteria in soils is also much different from that in oceans. In soil systems,80～90% bacteria are absorbed by soil particles. Though there are several studies about the adsorption of bacteria onto soil, few studies are on the adsorptive characteristics and the influence of environment factors on bacteria adsorption on soils with different components, especially the metabolism activity and oxidation activity of these adsorbed bacteria and thus their behaviors with respect to Mn(Ⅱ) oxidation are still not clear. In this study, a strain of Mn(Ⅱ)-oxidizing bacteria HN79 and four zoned soils (Calci-Aquic Vertosols, Hapli-Ustic Argosols, Claypani-Udic Argosols and Alliti-Udic Ferrosols) were chose. Three different treatments were applied to the clays (< 2μm) and hence resulted in three different types of samples:organic matter left on the samples (organic clay), organic matter removed from samples by H2O2 (inorganic clay) and free ferrite removed from samples by DCB (de-iron clay). The characteristics of Mn(Ⅱ)-oxidizing bacteria adsorption on clays were investigated with equilibrium adsorption method, and the characters of Mn(Ⅱ) oxidation by the HN79 adsorbed by organic clays were also investigated. The main results are as follows:1. A strain of Mn(Ⅱ)-oxidizing bacteria HN79 was isolated from the iron-manganese nodules in Guiyang, Hunan Province, South China. The phylogeny based on sequencing the 16S rDNA gene confirms that the bacteria is most-closely related to Bacillus cereus strain named HN79. 2. The adsorption isotherms of the bacteria on different soil clays can be well fitted with Langmuir equation. The amount of bacteria adsorbed on Calci-Aquic Vertosols, Hapli-Ustic Argosols and Claypani-Udic Argosols with different treatments follows the order:de-iron clay> organic clay> inorganic clay, As to Alliti-Udic Ferrosols, the sequence is de-iron clay> inorganic clay> organic clay. The affinities of HN79 onto different soil clays are in order:organic clay> inorganic clay> de-iron clay. The amount of bacteria absorbed by the soil clays was mainly determined by the SSA, the amount of iron oxide and organic matter in clays, and the affinities between HN79 and clays were mainly determined by the soil surface charge.3. The influence of variable environment conditions on the adsorption was different. The adsorption of HN79 on organic clays approaches equlibrium in 60 min, including instant and slow adsorption stages. Pseudo-second-order kinetic analysis for the adsorption of HN79 on different organic clays indicated that the rate constant (k) increased with the soil samples distributing from north to south. The adsorption of HN79 on Alliti-Udic Ferrosols reaches equilibrium the most quickly. The adsorption of HN79 on different organic clays increased initially, then decreased and finally stabilized with the increase of pH from 2.0 to 9.0. The adsorption of bacteria on Calci-Aquic Vertosols andHapli-Ustic Argosols reached the maximum at pH 4, while at pH 3 on Claypani-Udic Argosols and Alliti-Udic Ferrosols. Increasing the concentration of K+ from 0 to 10 mmol/L enhanced the level of HN79 adsorbed by clays, but the situation was changed when the concentration of K+ was higher than 10 mmol/L. Under the circumstances that the concentration of K+ ranged from 10 to 100 mmol/L, the adsorption of HN79 increased on Calci-Aquic Vertosols and Hapli-Ustic Argosols but decreased on Claypani-Udic Argosols and Alliti-Udic Ferrosols. A steady increase in bacteria adsorption was observed on four organic clays with increasing Mg+ concentrations. A percentage of 25.09%～60.73% of adsorbed bacteria on clays were released by pH 7.0,0.01 mol/L Tris-HCl buffer and KCl. The percent desorption of bacteria from clays by sodium phosphate buffer was 0.9～13.68%. The amount of desorbed bacteria on three treatments soil clays followed the sequence of de-iron clay> inorganic clay> organic clay. Dehydration effects, hydrogen band and other possibly chemical interactions dominated bacteria adsorption on organic clays, and bacteria were adsorbed predominantly via electrostatic interactions and dehydration effects by inorganic and de-iron clays.4. The investigations on adsorbed bacteria on soil clays by SEM showed that the bacteria not only adsorbed on soil surface, but also can be coated by soil clays. The morphology was different between adsorbed bacteria and free status bacteria which has regulated short columnar structure. The investigations on HN79 with different clays by FTIR indicated that carboxyl functionalities and amino groups on HN79 were mainly active sites responsible for the adsorption.5. Soil clays have much impact on the growth and oxidation activity of HN79. On one hand, soil clays improved the maximal growth rate and growth yield of HN79 in stationary stage. On the other hand, clays inhibited the Mn(Ⅱ) oxidation activity of HN79. HN79 almost lost the oxidation activity when adsorbed on soil surface. Only the bacteia adsorbed by clays via Lifshitz-van der Waals attractive forces and electrostatic forces retain the ability of oxidation of Mn(Ⅱ) to Mn(Ⅲ/Ⅳ).6. The sourish environment improved the bacteria growth but inhibited the activity of Mn(Ⅱ) oxidation. In this study we fonnd that the bacteria reached the log phase at pH 5 earlier 10～20 hours than pH7 and pH9. However, the oxidation rate of Mn(Ⅱ) by HN79 was lower 30.75% in acidity environment than in neutral. |
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