Effects of enrichmemt planting with native tree species on bacterial community structure and potential impact on Eucalyptus plantations in southern China

Multi-generational planting of Eucalyptus species degrades soil quality but the introduction of legumes can improve soil fertility and microbial diversity.However,the effects of introducing non-legume native tree species on soil nutrients and bacterial community structure remain poorly understood.This study investigated the impacts of the conversion of third generation monoculture Eucalyptus plantations to mixed systems including Eucalyptus urograndis with Cinnamomum camphora(EC)and E.urograndis with Castanopsis hystrix(EH),on soil chemical and biochemical properties and bacterial community structure,diversity and functions.First generation E.urophylla plantations were the control.Results show that planting the third generation Eucalyptus led to a significant decrease in p H,organic matter,nutrient content,enzyme activities(invertin,acid phosphataes,and urease),and bacterialα-diversity compare to the controls.However,the mixed planting showed significant improvement in soil chemical and biochemical attributes and bacterialα-diversity,although the E.urograndis and C.hystrix planting had no improvement.Chloroflexi(oligotrophic bacteria)were significantly enriched in third generation Eucalyptus and Eucalyptus+C.hystrix,while proteobacteria increased significantly in the E.urograndis with C.camphora plantings.The relative abundance of multiple metabolic pathways increased significantly in the third generation Eucalyptus plantations whereas membrane transportrelated genes were enriched in soils of the mixed systems.The changes in bacterial community structures in the two mixed systems were driven by diversity,organic matter and acid phosphatase,while bacterial functions were affected by invertase,NO_(3)^(-)-N,diversity and urease.These results suggest that the transformation of successive monoculture Eucalyptus plantations into mixed plantations reduces the depletion of soil nutrients and enhances the ecological function of soil microorganisms.

Inclusion of peanut in wheat–maize rotation increases wheat yield and net return and improves soil organic carbon pool by optimizing bacterial community

Improving soil quality while achieving higher productivity is the major challenge in the agricultural industry. Wheat(Triticum aestivum L.)–maize(Zea mays L.)(W–M) rotation is the dominant planting pattern in the Huang-HuaiHai Plain and is important for food security in China. However, the soil quality is deteriorating due to the W–M rotation’s long-term, intensive, and continuous cultivation. Introducing legumes into the W–M rotation system may be an effective way to improve soil quality. In this study, we aimed to verify this hypothesis by exploring efficient planting systems(wheat–peanut(Arachis hypogaea L.)(W–P) rotation and wheat rotated with maize and peanut intercropping(W–M/P)) to achieve higher agricultural production in the Huang-Huai-Hai Plain. Using traditional W–M rotation as the control, we evaluated crop productivity, net returns, soil microorganisms(SMs), and soil organic carbon(SOC) fractions for three consecutive years. The results indicated that wheat yields were significantly increased under W–P and W–M/P(382.5–579.0 and 179.8–513.1 kg ha-1, respectively) compared with W–M. W–P and W–M/P provided significantly higher net returns(58.2 and 70.4%, respectively) than W–M. W–M/P and W–M retained the SOC stock more efficiently than W–P, increasing by 25.46–31.03 and 14.47–27.64%, respectively, in the 0–20 cm soil layer. Compared with W–M, W–M/P improved labile carbon fractions;the sensitivity index of potentially mineralizable carbon, microbial biomass carbon(MBC), and dissolved organic carbon was 31.5, 96.5–157.2, and 17.8% in 20–40, 10–40, and 10–20 cm soil layers, respectively. The bacterial community composition and bacteria function were altered as per the soil depth and planting pattern. W–M/P and W–M exhibited similar bacterial community composition and function in 0–20 and 20–40 cm soil layers. Compared with W–P, a higher abundance of functional genes, namely, contains mobile elements and stress-tolerant, and a lower abundance of genes, namely,potentially pathogenic, were observed in the 10–20 cm soil layer of W–M and the 0–20 cm soil layer of W–M/P. SOC and MBC were the main factors affecting soil bacterial communities, positively correlated with Sphingomonadales and Gemmatimonadales and negatively correlated with Blastocatellales. Organic input was the main factor affecting SOC and SMs, which exhibited feedback effects on crop productivity. In summary, W–M/P improved productivity, net returns, and SOC pool compared with traditional W–M rotation systems, and it is recommended that plant–soil–microbial interactions be considered while designing high-yield cropping systems.

Changes in Cold and Hot Syndromes and Gastrointestinal Bacterial Community Structure in Mice by Intervention with Food of Different Nature

Objective:To reveal the effect of foods with different natures on cold or hot syndrome and gastrointestinal bacterial community structure in mice.Methods:Forty-five 6-week-old male ICR Kunming mice of clean grade were divided into 5 groups,9 per group,including the control(CK),hot nature herb medicine(HM),Hong Qu glutinous rice wine(RW),tea rice wine(TW),and cold nature herb medicine(CM)groups.Distilled water or corresponding herbs were administered to mice(0.01 mL/g body weight)in the 5 groups by gastric infusion respectively,once daily for 28 d.Appearance,behavior,and serum biochemical indicators,including 5-hydroxytryptamine(5-HT),thyroid stimulating hormone(TSH),noradrenaline(NE),cyclic adenosine monophosphate(cAMP)and cyclic guanosine monophosphate(cGMP),the hot nature index,as well as the gastrointestinal bacterial community structure were analyzed in all groups after treatment.Results:After supplementation for 28 d,CM and TW mice showed different degrees of cold syndrome,and HM and RW mice showed different degrees of hot syndrome.Compared with the HM and RW mice,the TSH,NE,cAMP levels and hot nature indices in the CM and TW mice were significantly decreased and 5-HT and cGMP levels were significantly increased(P<0.05).There was no obvious change in appearance or behavior in CK mice.Results of clustering analysis showed that the gastrointestinal bacterial community structures were highly similar in TW and CM mice as well as in RW and HM mice,and that they were from the same branch,respectively,when the distance was 0.02.The key microbes associated with cold syndrome were Lachnospiraceae uncultured,Lactococcus,etc.,and the key microbes associated with hot syndrome were S24-7 norank,Ruminococcaceae uncultured,etc.Conclusion:The interventions with different nature foods could change cold or hot syndrome in mice,leading to changes in gastrointestinal bacterial community structure.

Effect of reclaimed water effluent on bacterial community structure in the Typha angustifolia L. rhizosphere soil of urbanized riverside wetland, China

In order to evaluate the impact of reclaimed water on the ecology of bacterial communities in the Typha angustifolia L. rhizosphere soil, bacterial community structure was investigated using a combination of terminal restriction fragment length polymorphism and 16S rRNA gene clone library. The results revealed significant spatial variation of bacterial communities along the river from upstream and downstream. For example, a higher relative abundance of γ-Proteobacteria, Firmicutes, Chloroflexi and a lower proportion of β-Proteobacteria and ε-Proteobacteria was detected at the downstream site compared to the upstream site. Additionally, with an increase of the reclaimed water interference intensity, the rhizosphere bacterial community showed a decrease in taxon richness, evenness and diversity. The relative abundance of bacteria closely related to the resistant of heavy-metal was markedly increased, while the bacteria related for carbon/nitrogen/phosphorus/sulfur cycling wasn＇t strikingly changed. Besides that, the pathogenic bacteria markedly increased in the downstream rhizosphere soil since reclaimed water supplement, while the possible plant growth-promoting rhizobacteria obviously reduced in the downstream sediment. Together these data suggest cause and effect between reclaimed water input into the wetland, shift in bacterial communities through habitat change, and alteration of capacity for biogeochemical cycling of contaminants.

Impacts of methamidophos,copper,and their combinations on bacterial community structure and function in black soil

The potential ecotoxicologial risks of methamidophos,copper,and their combinations on microbial community of black soil ecosystem in the Northeast China were assessed in species richness and structures by using 16S rDNA-PCR-DGGE analysis approach,and functional characteristics at community levels by using BIOLOG^(GN) system analysis method as well as two conventional methods(DHA and SIR).All results of DGGE banding fingerprint patterns(amplified by bacterial specific 16S rDNA V_(3) high variable region universal primer)indicated that the species richness of bacterial community in tested soil was significantly decreased to different extents by using different concentrations of single methamidophos,copper,especially some of their combinations had worse effects than their corresponding single factors.In addition,the structures of soil bacterial community had been disturbed under all stresses applied in this study because of the enrichment of some species and the disappearance of other species from the bacterial community.The effects of the single factors with lower concentrations on the communiy structure were weaker than those with higher concentrations.Moreover,the bacterial community structures under the combined stresses of methamidophos and copper were significantly different from those of control and their corresponding single factors.The change of DHA and carbon source substrate utilizing fingerprint patterns based on BIOLOG^(GN)system were two relatively sensitive directors corresponding to the stress presented in this study.Between methamodophos and copper,there happened the significant joint-toxic actions when they were used in combination on DHA and carbon source substrate utilizing fingerprint patterns of soil bacterial communities.The DHA of soil under the combined stresses was lower than that of the control and that under the single factors,and the BIOLOG^(GN) substrate utilizing patterns of soil treated by combinations were distinctively differentiated from the control and their corresponding single factors.From all of above,the methamidophos,copper,especially their combinations had the clearly potential ecotoxicological risks to influence the natural soil microbial ecological system by changing the structure,richness,and the functional characteristics of microbial community.

Wheat, maize and sunflower cropping systems selectively influence bacteria community structure and diversity in their and succeeding crop's rhizosphere

supported by the Special Fund for Agro-scientific Research in the Public Interest in China （201103001）

PCR-DGGE Analysis of Bacterial Communities Structure in Babylonia areolata Culture Systems of The Subtidal Zone and The Pond Mulched Plastic Film and Sand in Bottom

To know the bacterial communities structure in Babylonia areolata culture systems and to research and optimize the management pattem of Babylonia areola-ta culture systems of the pond mulched plastic film and sand in bottom, the bacte- rial communities in Babylonia areolata culture systems of the sub-tidal zone and the pond mulched plastic film and sand in bottom were analyzed at molecular level by adopting the denaturing gradient gel electrophoresis （DGGE）. The results indicated that the dominant bacterial communities in Babylonia areolata culture systems of the sub-tidal zone and the pond mulched plastic film and sand in bottom, which were built on the basis of the seawater in East-island of Zhanjiang, included Proteobac- teda Chloroflexi, Cyanobacteria and Actinobacteria. The dominant bacterial groups in the above pond culture system were Garnmaproteobacteria, Alphaproteobacteria, Deltaprotecbacteda, Epsilonproteobacteda, Anaerolineae, Cyanobacteria and Acti- nobacteda. The dominant bacterial communities in the subtidal zone culture system were Gammaprotecbacteda, Alphaproteobacteria, Deltaproteobacteria, Anaerolineae and Cyanobacteda, and there were less Epsilonproteobacteria and Actinobacteria in the culture system. The higher diversity was detected in the above two culture sys- tems. The results of unweighted pair group method with arithmetic average （UPG- MA） showed that the bacterial communities of the sediment samples S1 and S2 in the above two culture systems were a cluster, the similarity of bacterial communities was 54.5%. The bacterial communities of seawater samples S3 and S4 in the above culture systems were in clusters, and the similarity of the bacterial communi- ties was 84.0%. The results showed that the microorganism ecological level in the Babylonia areolata culture systems of the pond mulched plastic film and sand in bottom could be similar to the sub-tidal zone culture systems through changing the pond seawater and monitoring the microbial population.

Soil bacterial characteristics between surface and subsurface soils along a precipitation gradient in the Alxa Desert, China

Bacteria in desert soil have unique phylogeny and important ecological functions, and theirresponses to changes in precipitation need further attention. However, relevant studies have mainlyfocused on the surface soil, and studies on the responses of bacteria at different soil depths to variationsin precipitation are rare. Thus, we used 16S rDNA high-throughput sequencing to investigate the changesin soil bacterial distribution along a mean annual precipitation gradient (50–150 mm) in the Alxa Desert,China, and compared the variation characteristics in the surface soil layer (0–10 cm) and subsurface soillayer (10–20 cm). Results showed that soil bacterial communities significantly changed along theprecipitation gradient in both soil layers. However, the subsurface soil layer could support bacterialcommunities with higher diversity and closer internal relationships but more internal competition than thesurface soil layer. Additionally, compared with the surface soil layer, variations in diversity andco-occurrence patterns in the subsurface soil layer were more in line with the changes in the mean annualprecipitation, while bacterial community structure was less variable in the subsurface soil layer. Comparedwith the mean annual precipitation, soil moisture had little influence on the structure and diversity of soilbacterial community but had a high correlation with intercommunity connectivity. Therefore, soilmoisture might play a complex role in mediating environmental conditions and soil bacterial communitycharacteristics. Due to the different responses of surface and subsurface soil bacteria to the changes inprecipitation, it is necessary to distinguish different soil layers when predicting the trends in desert soilbacterial conditions associated with precipitation, and prediction of subsurface soil bacteria may be moreaccurate.

Microbial community study in a petrochemical industry wastewater treatment system by PCR-DGGE

To improve the efficiency of petrochemical wastewater purification, the relationship between bacterial community structure and pollutants loading/degrading rates in A/O process for petrochemical wastewater treatment was investigated by denaturing gradient gel eleetrophoresis （DGGE） of the 16S rRNA gene fragments amplified by polymerase chain reaction （PCR）. Results show that while the influent COD and NH4^＋ -N concentrations are 425.92 -560 mg/L and 64 - 100 mg/L respectively, the corresponding average concentrations of the effluent are 160 mg/L and 55 mg/L, which are 1. 6 and 3.6 times more than the national standards respectively. It demonstrates that the performance of pollutants removal process is inefficient. The analysis of PCR-DGGE profile indicates that the bacterial community structure of the activated sludge in A/O system is species-rich but unstable, and the highest and the lowest similarity coefficients are 36% and 6. 25% respectively, which shows that remarkable community structure evolution exists in the system. The variation of bacterial community structure and pollutants loading influences the removal efficiency of pollutants obviously, and relatively stable com- munity structure leads to the stable operational performance of biological wastewater treatment system.

Screening and degrading characteristics and community structure of a high molecular weight polycyclic aromatic hydrocarbon-degrading bacterial consortium from contaminated soil

Inoculation with efficient microbes had been proved to be the most important way for the bioremediation of polluted environments. For the treatment of abandoned site of Beijing Coking Chemical Plant contaminated with high level of high-molecular-weight polycyclic aromatic hydrocarbons （HMW-PAHs）, a bacterial consortium capable of degrading HMW-PAHs, designated 1-18-1, was enriched and screened from HMW-PAHs contaminated soil. Its degrading ability was analyzed by high performance liquid chromatography （HPLC）, and the community structure was investigated by construction and analyses of the 16S rRNA gene clone libraries （A, B and F） at different transfers. The results indicated that 1-18-1 was able to utilize pyrene, fluoranthene and benzo[a]pyrene as sole carbon and energy source for growth. The degradation rate of pyrene and fluoranthene reached 82.8% and 96.2% after incubation for 8 days at 30℃, respectively; while the degradation rate of benzo[a]pyrene was only 65.1% after incubation for 28 days at 30℃. Totally, 108, 100 and 100 valid clones were randomly selected and sequenced from the libraries A, B, and E Phylogenetic analyses showed that all the clones could be divided into 5 groups, Bacteroidetes, ct-Proteobacteria, Actinobacteria, β-Proteobacteda and γ- Proteobacteria. Sequence similarity analyses showed total 39 operational taxonomic units （OTUs） in the libraries. The predominant bacterial groups were α-Proteobacteria （19 OTUs, 48.7%）, γ-Proteobacteria （90TUs, 23.1%） and β-Proteobacteria （80TUs, 20.5%）. During the transfer process, the proportions of α-Proteobacteria and β-Proteobacteria increased greatly （from 47% to 93%）, while γ-Proteobacteda decreased from 32% （library A） to 6% （library F）; and Bacteroidetes group disappeared in libraries B and F.

Enhanced nitrogen removal at low temperature with mixed anoxic/oxic process

Different hydraulic retention times(HRTs)were tested in a mixed anoxic/oxic(A/O)system at 5C and 10C to investigate the effects of HRT and carrier on nitrogen removal in wastewater at low temperatures.The results showed that the addition of the fillers improved the treatment effect of each index in the system.With an optimal HRT of 7.5 h at 5C,the removal efficiencies of NHþ4-N and total nitrogen(TN)reached 91.2%and 75.6%,respectively.With an HRT of 6 h at 10C,the removal efficiencies of NHþ4-N and TN were 96.7%and 82.9%,respectively.The results of high-throughput sequencing showed that the addition of the suspended carriers in the aerobic zone could improve the treatment efficiency of nitrogen at low temperatures.The microbial analysis indicated that the addition of the suspended carriers enhanced the enrichment of nitrogen removal bacteria.Nitrospira,Nitrotoga,and Nitrosomonas were found to be the bacteria responsible for nitrification,and their relative concentrations on the biofilm at 5C and 10C accounted for 98.11%,92.79%,and 69.98%of all biological samples,respectively.

Influence of cadmium and copper mixtures to rhizosphere bacterial communities

To study the effects of combined Cd and Cu pollution on rhizosphere bacterial community.High-throughput sequencing was used to examine the response of rhizosphere bacterial communities to heavy-metal stress under single and mixed pollution of cadmium(Cd)and copper(Cu).With additions of Cd and Cu,the mean diversity index of rhizosphere bacterial community was in the order Cu alone>Cd-Cu mixtures>Cd alone.In all Cd and Cu treatments,the dominant phyla were Proteobacteria,Actinobacteria,Chloroflexi and Acidobacteria.In the additions with different concentrations of Cd-Cu mixtures,LEfSe indicated that there were differences in the predominant species of rhizosphere bacterial communities.Some genera such as Streptomyces and Microbacterium belonging to Actinobacteria as biomarkers were significantly enriched in both control and treatments,while some genera such as Pseudoxanthomonas and Rhodopseudomonas belonging to Proteobacteria as biomarkers were observed to be enriched in the additions with single and mixture of Cd and Cu.According to the Nonmetric multidimensional scaling(NMDS)analysis,the structure of rhizosphere bacterial community was different between treatments and the CK.Principal Component Analysis(PCA)and permutational multivariate analysis of variance(PERMANOVA)showed that there were significant differences among treatments(p<0.01),and that the addition of Cu might be the primary factor affecting the composition of rhizosphere bacterial communities.

Effect of Rhizobacterium Rhodopseudomonas palustris Inoculation on Stevia rebaudiana Plant Growth and Soil Microbial Community

There is an increasing concern that the continuous use of chemical fertilizers might lead to harmful effects on soil ecosystem.Accordingly, a biocompatible approach involving inoculation of beneficial microorganisms is presented to promote plant growth and simultaneously minimize the negative effect of chemical fertilizers. In this study, Rhodopseudomonas palustris, a plant growth-promoting rhizobacterium(PGPR), was inoculated into both fertilized and unfertilized soils to assess its influence on Stevia rebaudiana plant growth and microbial community in rhizosphere soils in a 122-d field experiment. Soil enzyme assays(dehydrogenase, urease, invertase, and phosphomonoesterase), real-time quantitative polymerase chain reaction(RT-_qPCR), and a high-throughput sequencing technique were employed to determine the microbial activity and characterize the bacterial community. Results showed that the R.palustris inoculation did not significantly influence Stevia yields and root biomass in either the fertilized or unfertilized soil. Chemical fertilization had strong negative effects on soil bacterial community properties, especially on dehydrogenase and urease activities.However, R. palustris inoculation counteracted the effect of chemical fertilizer on dehydrogenase and urease activities, and increased the abundances of some bacterial lineages(including Bacteroidia, Nitrospirae, Planctomycetacia, Myxococcales, and Legionellales). In contrast, inoculation into the unfertilized soil did not significantly change the soil enzyme activities or the soil bacterial community structure. For both the fertilized and unfertilized soils, R. palustris inoculation decreased the relative abundances of some bacterial lineages possessing photosynthetic ability, such as Cyanobacteria, Rhodobacter, Sphingomonadales, and Burkholderiales. Taken together, our observations stress the potential utilization of R. palustris as PGPR in agriculture, which might further ameliorate the soil microbial properties in the long run.

Spatial and seasonal variations in bacterial communities of the Yellow Sea by T-RFLP analysis

Four typical coastal sites(rocky shore,sandy shore,mud flat shore,and artificial harbor)at the Yellow Sea were chosen to investigate the spatial and seasonal variations in bacterial communities.This was accomplished by using terminal restriction fragment length polymorphism(T-RFLP)analysis of PCR amplified 16S rDNA fragments.Two kinds of tetrameric restriction enzymes,HhaI and MspI,were used in the experiment to depict the bacterial community diversity in different marine environments.It was found that the community compositions digested by the two enzymes separately were different.However,the results of bacterial community diversity derived from them were similar.The MDA analysis results of T-RFLP profiles coming from HhaI and MspI both exhibited a significant seasonal community shift for bacteria and a relatively low spatial variation among the four locations.With HhaI as the sample,the pair wise Ttests also revealed that variations were minor between each pair of marine environments,with R ranging from 0.198 to 0.349.However,the bacterial community structure in the mud flat site depicted a larger difference than each of the other three sites(R ranging from 0.282 to 0.349).

Influence of pore structure on biologically activated carbon performance and biofilm microbial characteristics

Optimizing the characteristics of granular activated carbon(GAC)can improve the performance of biologically activated carbon(BAC)filters,and iodine value has always been the principal index for GAC selection.However,in this study,among three types of GAC treating the same humic acidcontaminated water,one had an iodine value 35%lower than the other two,but the dissolved organic carbon removal efficiency of its BAC was less than 5%away from the others.Iodine value was found to influence the removal of different organic fractions instead of the total removal efficiency.Based on the removal and biological characteristics,two possible mechanisms of organic matter removal during steady-state were suggested.For GAC with poor micropore volume and iodine value,high molecular weight substances(3500–9000 Da)were removed mainly through degradation by microorganisms,and the biodegraded organics(soluble microbial by-products,<3500 Da)were released because of the low adsorption capacity of activated carbon.For GAC with higher micropore volume and iodine value,organics with low molecular weight(<3500 Da)were more easily removed,first being adsorbed by micropores and then biodegraded by the biofilm.The biomass was determined by the pore volume with pore diameters greater than 100μm,but did not correspond to the removal efficiency.Nevertheless,the microbial community structure was coordinate with both the pore structure and the organic removal characteristics.The findings provide a theoretical basis for selecting GAC for the BAC process based on its pore structure.

Vertical distribution patterns and drivers of soil bacterial communities across the continuous permafrost region of northeastern China

Background:Soil microorganisms in the thawing permafrost play key roles in the maintenance of ecosystem function and regulation of biogeochemical cycles.However,our knowledge of patterns and drivers of permafrost micro-bial communities is limited in northeastern China.Therefore,we investigated the community structure of soil bacteria in the active,transition and permafrost layers based on 90 soil samples collected from 10 sites across the continuous permafrost region using high-throughput Illumina sequencing.Results:Proteobacteria(31.59%),Acidobacteria(18.63%),Bacteroidetes(9.74%),Chloroflexi(7.01%)and Actinobacteria(6.92%)were the predominant phyla of the bacterial community in all soil layers;however,the relative abundances of the dominant bacterial taxa varied with soil depth.The bacterial community alpha-diversity based on the Shannon index and the phylogenetic diversity index both decreased significantly with depth across the transition from active layer to permafrost layer.Nonmetric multidimensional scaling analysis and permutation multivariate analysis of variance revealed that microbial community structures were significantly different among layers.Redundancy analysis and Spearman’s correlation analysis showed that soil properties differed between layers such as soil nutrient content,temperature and moisture mainly drove the differentiation of bacterial communities.Conclusions:Our results revealed significant differences in bacterial composition and diversity among soil layers.Our findings suggest that the heterogeneous environmental conditions between the three soil horizons had strong influences on microbial niche differentiation and further explained the variability of soil bacterial community structures.This effort to profile the vertical distribution of bacterial communities may enable better evaluations of changes in microbial dynamics in response to permafrost thaw,which would be beneficial to ecological conservation of permafrost ecosystems.

Diversity and Characterization of Potential H_2-Dependent Fe(Ⅲ)-Reducing Bacteria in Paddy Soils

Microbial ferric iron reduction, with organic carbon or hydrogen as the electron donor, is one of the most important biogeochemical processes in anoxic paddy soils; however, the diversity and community structure of hydrogen-dependent dissimilatory iron-reducers remain unknown. Potential H2-dependent Fe（III）-reducing bacteria in paddy soils were explored using enrichment cultures with ferrihydrite or goethite as the electron acceptor and hydrogen as the electron donor. Terminal restriction fragment length polymorphism （T-RFLP） analysis and cloning/sequencing were conducted to reveal bacterial community structure. Results showed that Geobacter and Clost^dium were the dominant bacteria in the enrichment cultures. Fe（III） oxide mineral phases showed a strong effect on the community structure; Geobaeter and Clostridium were dominant in the ferrihydrite treatment, while Glostridium spp. were dominant in the goethite treatment. These suggested that H2-dependent Fe（lII）-redueing bacteria might be widely distributed in paddy soils and that besides Geobacter, Clostmdium spp. might also be an important group of H2-dependent Fe（III）-reducing microorganisms.