Studies On Community Composition And Diversity Of Mn(Ⅱ)-oxidizing Bacteria From Stratified Fe-Mn Nodules Surrounding Soils

Mn(II)-oxidizing bacteria are phylogenetically diverse assemblage, which is characterized by the ability to catalyze the oxidation of soluble Mn(II) to insoluble Mn(III, IV) oxides. Mn(III, IV) oxide minerals are capable of influencing significantly the transport and fate of both contaminants and nutrients in the environments through sportive, catalytic and oxidative processes and crucial in the biogeochemical cycles of many metals and organic substances, which have been to a major concerns. Now, most bacteria researched for Mn(II) oxidization are from marine, lake, submarine deposits etc, However, those from are less reported as well as the mechanisms of formation of biogenic manganese oxides. This study was to investigate the community composition and diversity of Mn(II)-oxidizing bacteria from stratified Fe-Mn nodules surrounding soils, using culture-dependent and-independent methods.Three stratified soil samples from surface soil layer, subsoil layer and substratum, which were named A-, B-and C-horizon, respectively, were taken from soil with a spot of scattered ferromanganese nodules at Queyu, Shandong Province, and performed to analyse its chemistry characteristic and isolate bacteria, which were all used to determinate the Mn(II)-oxidizing activity. It showed this soil was alkalescent and had high levels of MnO2 and Fe2O3. There were 503 bacteria isolated from this soil,192 from A-horizon,160 from B-horizon,151 from C-horizon respectively. Besides, isolates with Mn(II)-oxidizing activity accounted for 68.4%, of which the Mn(II)-oxidizing isolates from A-horizon were the most. However, those with high Mn(II)-oxidizing activity were mainly distributed on B-and C-horizon, accounted for 13.8% and 13.2% respectively.Only the bacteria with high Mn(II)-oxidizing activity were performed to PCR of 16S rRNA gene, ARDRA(Amplified rDNA restriction analysis), sequence and alignment.50 high Mn(Ⅱ)-oxidizing bacteria were found to compose of 24 genra of bacteria and primarily belonged to Firmicutes, Actinobacteria and Proteobacteria (α-、β-andγ-subdivisions), of which 7 genra were first found to have the activity of Mn(II) oxidization. The dominant Mn(II)-oxidizing bacteria detected in A-horizon soil was found to be Firmicutes group species, being mainly composed of Bacillus. However most of high Mn(Ⅱ)-oxidizing isolates from the deeper B-and C-horizon soils were belonged to phylum Actinobacteria While the proportion of those belonging to Proteobacteria in different-depth soil were equivalent.In order to monitor the effect of Mn(Ⅱ) on the soil bacteria diversity, we enriched the soil with K medium within different Mn(Ⅱ) concentrations and sampled at the first day, third day, seventh day and eleventh day during enrichment, meanwhile, used DGGE (Denaturing Gradient Gel Electrophoresis) to reflect intuitively the changes of bacterial diversity as different concentration Mn(Ⅱ), togethering with the imagine analysis software, which could make the analytic results more scientifically. It showed that the diversity of soil bacterial community declined with increased depths, but significantly increased after enriching with Mn(Ⅱ). Moreover, The soil bacteria were tolerant to Mn(Ⅱ), especially for A-horizon, of which the average bacteria diversity was the maximum when it was enriched with 10 mM Mn(Ⅱ). But the maximum average bacteria diversity of B-and C-horizon happened when it was enriched with 0 mM and 1 mM Mn(Ⅱ) respectively. Besides, we randomly excised 37 predominant DGGE bands, after clone and sequence, and found they mainly belonged to Firmicutes, and Proteobacteria (β-andγ-subdivisions), which was similar to the culturable Mn(Ⅱ)-oxidizing bacteria. All investigations above showed the accordance of the diversity and community compositon of Mn(Ⅱ)-oxidizing bacteria in this soil environment with the Mn(Ⅱ) oxidization, and the similarity in phyletic evolution of Mn(Ⅱ)-oxidizing bacteria from terrestrial and aqueous environment. These indirectly reflected the role of those bacteria in forming the manganese oxide minerals.