| The soluble Mn(Ⅱ)could be oxidized to be Mn(Ⅲ,Ⅳ) oxides by some bacteria and fungi. Most of the studies were carried out with marine microbes under unadsorbed situation. However, microbes in terrestrial ecosystem are mostly adsorbed by soil particls. The impacts of adsorption by soil particls on Mn-oxidizing bacteria growth and Mn(Ⅱ)oxidation were rarely reported. Mn-oxidizing bacterium strain HN79 was screened from iron-manganese nodules in red soil. The adsorption characteristics of HN79 on clay minerals (montmorillonite, goethite, kaolinite and illinite) were investigated. The growth curve and Mn(Ⅱ)oxidation of adsorbed bacteria and free bacteria were also investigated. The following results are as followed:1. HN79 is gram positive Bacillus, rod-shaped. The specific-surface area of HN79 was 1.41m2/g. Surface charge of bacteria was -4.46 umol/m2.2. The condition of cells lysis and the optimal method for determining the amount of bacteria were ascertained. The cracking time in NaOH solution was 30 min. The concentration of NaOH was 0.4 mol/L. Take 0.5 mL protein filtrate as coloration volume and the volume of chromogenic agent (CBB) was 5 mL. Sucrose of 70% (w/v) was used to separate free cells from adsorbed bacteria by centrifuging. The centrifugal speed was 4,000 r/min.3. The adsorption isotherms of HN79 on four kinds of clay minerals were fitted well with Langmuir model. The maximum adsorption quantity of bacteria followed the order:montmorillonite (40.86×109 cells/g)> kaolinite (28.10×109 cells/g) goethite (26.13×109cells/g)> illite (16.78×109 cells/g). While the binding strength (K value) followed the order of goethite> illite> kaolinite> montmorillonite. With the ionic strength increasing, the number of adsorbed bacteria increased firstly, and then decreased until stabilization. There was a marked decrease in the amount of adsorbed bacteria on minerals when pH increaseed. The saturated adsorption of bacteria on clay mineral, which were desorbed by Tris-HCl, KCl and NaH2PO4-Na2HPO4 respectively, had the following desorption characteristics: the maximum desorption number of bacteria which desorbed by KCl in four mineral-bacteria complex, a minimum desorption number which desorbed by 4. Using the above three desorption agents to successively desorb the bacteria which saturated adsorption onto clay mineral surface, the percent of desorption followed the order:Tris-HCl> KCl> Na2HPO4-NaH2PO4. The isometric adsorption system had the opposite rule, and the total desorption rate of saturated sorption system far outweighed that of the isometric adsorption system.4. Combined with the results of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). The hydroxy, phosphoric acid and carboxyl were all involved in the adsorption processes on bacteria cell surface, and there was forming hydrogen bonding between bacteria and goethite. In short, the van der Waals force and electrostatic force were the main forces governing the sorption of the bacteria on montmorillonite and kaolinite; For goethite, the chief adsorption force were the ligand exchange and hydrogen bonding force; Electrostatic force, which was considered to be one of the major forces controlling the sorption of HN79 on illinite, has a stable adsorption affinity.5. The growth of different absorbed bacteria on different mineral and Mn(Ⅱ)oxidization characteristics were discussed. In the coexisting system, minerals were all promoted bacteria proliferation. In saturated adsorption system, clay minerals not only had stimulative impact on bacteria biomass, but also had the inhibitory role on bacteria stage. Particularly, montmorillonite had obvious stimulative effect on bacterial growth. The surface characteristics of clay minerals affected Mn(Ⅱ)oxidization. Mn(Ⅱ)oxidization capacity of different minerals-bacteria complex followed the order of montmorillonite> goethite> kaolinite≈illite.6. The bacterial growth and Mn (Ⅱ) oxidation characteristics of adsorbed bacteria on minerals, after desorbed adsorption by different desorption agent were determined. The growth rate of four kinds of adsorbed bacteria on minerals growth, was slower than that of free bacteria, especially for that desorbed by KCl. Montmorillonite could promote adsorbed bacteria’s growth, shortened the lag period, while the other three clay minerals all inhibited the growth of HN79. The average oxidation rate of three groups desorbed adsorption bacteria followed the sequence of NaH2PO4-Na2HPO4 (8.27%)> Tris-HCl (4.76%)> KCl(1.39%). The types of adsorption force between bacteria and mineral affected bacterial growth and metabolism, thereby had an impact on Mn (Ⅱ) oxidation. The bacteria which were absorbed by van der Waals force and electrostatic force played a chief role on Mn (Ⅱ) oxidation. While the bacteria specific adsorption bacteria played the minor.7. Manganese oxides formed by HN79 and minerals-bacteria complex were flocculent and granular, which were coated by absorbed bacteria. Many of them were short-range orderly, weak-crystalline nanoscale structure. They were identified as hausmannite by XRD. |
PDF Full Text Request