Paddy Field Soil Research Articles

Complete Genome Sequence of Ferrigenium kumadai An22, a Microaerophilic Iron-Oxidizing Bacterium Isolated from a Paddy Field Soil.

ABSTRACTFerrigenium kumadai An22T (= JCM 30584T = NBRC 112974T = ATCC TSD-51T) is a microaerophilic iron oxidizer isolated from paddy field soil and belongs to the family Gallionellaceae. Here, we report the complete genome sequence of F. kumadai An22T, which was obtained from the hybrid data of Oxford Nanopore long-read and Illumina short-read sequencing.

Accumulation risk and source apportionment of heavy metals in different types of farmland in a typical farming area of northern China.

The types of land used for farmland can greatly influence the source and accumulation risk of heavy metals in soil. However, the apportioning quantitatively the source of soil heavy metals has been studied insufficiently, especially in terms of different types of farmland. In this study, a total of 252 soil samples were taken from dry land, paddy fields and greenhouse fields in the Jinyuan district of Taiyuan city, China, to assess the accumulation risk of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn). The results were then integrated, and source apportionment was evaluated by geospatial analysis, multivariate statistical analysis and positive matrix factorization (PMF). Cr, Cd and Hg were the dominant pollutants in the studied area. Accumulation risk by Cd and Cu was more severe in greenhouse fields than in dry land or paddy fields, whereas As, Hg and Pb had relatively higher accumulation in paddy fields than in dry land or greenhouse fields. Hg was derived mainly from coal combustion by atmospheric precipitation for the three types of farmland. Long-term irrigation using sewage is the main reason for the accumulation of Cu and Ni in dry land soil, Cu and Zn in paddy field soil and Zn in greenhouse soil. Cd in dry land, Cd and Pb in paddy fields and Cd, Cu, Ni and Pb in greenhouse fields were primarily added to soil through fertilization. Sewage irrigation and fertilization were the dominant sources of heavy metals for paddy field (31.3%) and greenhouse field (33.1%), respectively.

Efficiency of carbon sorbents in mitigating polar herbicides leaching from tropical soil

Imidazolinones are a group of herbicides with high potential of leaching and long half-lives that are posing a threat to water resources’ quality especially in tropical areas. Biochar, a carbon-rich bio-sorbent, has shown its ability to stabilise organic substances in soils and therefore, potentially is able to reduce their leaching. Biochar is a sustainable and cost-effective material which can be produced from locally available wastes. This work, for the first time, evaluated the biochar’s effects on leaching of two polar members of imidazolinones family namely imazapic and imazapyr, and also Onduty® which is a mixture of these two herbicides, in heavy soil of tropical paddy fields. Leaching columns accompanied with artificial irrigation were used during the laboratory experiment. The herbicides were extracted from both collected leachates and soil columns. Soil amendment with designed biochars significantly reduced the herbicides’ leaching percentages. Oil palm empty fruit bunch (OPEFB) and rice husk (RH) were used as pyrolysis feedstock. About 16% of the applied imazapic was leached out from biochar-free soil. For RH and OPEFB biochar-amended soils, the amounts were 4.3% and 3.6%, respectively. The highest percentage of imazapyr leached out from non-amended soil was (14.2%) followed by RH (4.0%) and OPEFB (2.8%) in biochar-amended soils. Also, 15.2% of the applied Onduty® was leached from non-amended soil. Adding RH and OPEFB biochars could reduce the herbicide leaching to 4.2% and 3.0%, respectively. Soil amended with biochars retained the higher percentages of the herbicides in top 7.5 cm depths. The media sorption capacities were negatively correlated to the amounts of herbicides leached out from soils but positively to the amounts of the herbicides remaining in the soil. Total amount of herbicides adsorbed by biochars-amended soils was more than 95%. Cation/water bridging ion exchange, ligand exchange, electrostatic attraction, and hydrophobic partitioning are the main ways imidazolinones can be adsorbed to soil. It was concluded that biochar application has the potential to reduce polar imidazolinones’ leaching and their environmental pollution. The custom-engineered biochars can specifically control the pesticides transfer and then can certainly enhance the biochars’ commercial values for their applications in the environment.

Characterization and distribution of different phosphorus types in the agricultural areas of Daecheong Lake Watershed, South Korea.

Agricultural areas utilize various types of agrichemicals to enhance crop growth and production. As a consequence, areas treated with excessive amounts of agrichemicals become primary sources of environmental pollutants. This study was conducted to analyze the different types of phosphorus (P) in the agricultural soils in Deacheong Lake Watershed. The effects of cultivation activities in the availability of nutrients that can potentially cause eutrophication of receiving water bodies were also assessed. The total phosphorus (T-P) and phosphate (PO4-P) concentrations in the tributaries draining into the Daecheong Lake were found to be three to seven times higher than the T-P and PO4-P concentrations in Daecheong Lake. The P concentrations in the waterways exhibited significant correlations (p < 0.05) with the soil P, implying that agricultural activities may influence the water quality in Daecheong Lake. Dry field soils had higher T-P concentrations (1246.1 ± 579.9 mg/kg) as compared to paddy fields and in situ soils due to the continuous accumulation of P in the soil strata. Non-apatite inorganic phosphorus (NAI-P) was the most dominant type of P in paddy field soils, whereas organic-P had the highest fraction in dry field soils. Paddy fields can have higher potentials of contributing to eutrophication, since NAI-P is an indicator of algal-available P. T-P concentrations in agricultural soils planted with different crops follows the order: tobacco > corn > perilla > soybean > Chinese cabbage > barley > sweet potato > garlic > potato > red pepper > rice. Generally, shifts in agricultural practices can be used to assess the contribution of agricultural areas in the eutrophication potential of water bodies.

Mercury methylation and its accumulation in rice and paddy soil in degraded lands: A critical review

Rice and paddies soil in the mining degraded areas are mostly contaminated with toxic metals like mercury (Hg) Hg is a global pollutant which can change into methylmercury (MeHg), the highly toxic and bio-accumulative organic form. This review paper highlights various aspects of Hg including its methylation and uptake by rice (a staple food) in degraded soil and its associated human health effects. It has been found that MeHg in rice grown in unrestrained MeHg areas close to mining degraded sites, contain over (100 μ g/kg) in the edible part (grain) and shown to be over ten times higher than other food crops. This manuscript examines Hg speciation in paddy field soils with various levels of Hg contamination. Many factors including types of soils, pH, organic matter, sulfur, light, oxygen availability, manganese (Mn) and iron oxides, temperature etc. affect the methylation and bioavailability of Hg. In Hg mining regions rice intake appears to be the primary MeHg exposure pathway. On health side the studies regarding MeHg gastrointestinal absorption have indicated a huge percentage of MeHg absorption in the body. Rice is considered as the second major source of MeHg for human exposure and health risk. Furthermore the various factors and mechanisms responsible for Hg speciation in degraded soil, Hg bioavailability, rice plant uptake, health risk of human, future research gaps and needs are also addressed and identified in this review paper. • Industrialization/urbanization have caused Hg contamination of paddy soil and rice. • Soil physico-chemical properties and bacteria affect Hg methylation and availability. • Various mechanisms responsible for Hg speciation are discussed. • Hg-methylation and uptake by rice leads to human health risk such as cancer.

Analysis of Adhesion between Wet Clay Soil and Rotary Tillage Part in Paddy Field Based on Discrete Element Method

To analyze the process of wet clay soil adhering to the rotary tillage part during rotary tillage in paddy field, simulation tests were carried out based on the discrete element method (DEM) in this study. The Plackett-Burman (PB) test was applied to obtain simulation parameters that significantly affected the soil adhesion mass. The Box-Behnken design (BBD) based on the principle of response surface method (RSM) was used to establish a regression model between significant parameters and soil adhesion mass. The soil adhesion mass obtained from the actual soil bin test as the response value was brought into the regression model. The optimal simulation parameters were obtained: the particle-particle coefficient of rolling friction, the particle-geometry coefficient of static friction, and the particle-particle JKR (Johnson-Kendall-Roberts) surface energy were 0.09, 0.81, and 61.55 J·m−2, respectively. The reliability of the parameters was verified by comparing the soil adhesion mass obtained under the optimal simulation parameters with the actual test value, and the relative error was 1.84%. Analysis of the rotary tillage showed that soil adhesion was mainly concentrated in the sidelong section of the rotary blade. The maximum number of upper soil particles adhering to the rotary tillage part was 2605 compared to the middle soil and lower soil layers. The longer the distance the rotary tillage part was operated in the soil for, the more soil particles would adhere to it. This study can provide a reference for the rational selection of simulation parameters for rotary tillage and the analysis of soil adhesion process in rotary tillage.

Novel methanotrophic and methanogenic bacterial communities from diverse ecosystems and their impact on environment

Methane oxidizing and methane releasing bacterial communities are very pioneer microbial population, abundantly present in several ecosystems. The microbial dynamics and metabolic assemblages are positively affected by these peculiar groups of bacteria, playing very important role in sustaining carbon geochemical cycle. A number of conventional methanotrophic and methanogenic communities are reported from marine and coastal environment, forest/desert ecosystem, paddy field soil, fresh water lakes, swamps and other soil ecosystems. In rice fields, both bacterial populations are complementary to each other. Methane gas is released by one community while utilized by another community through oxidation process. The present review describe novel species belonging to methanotrophic and methanogenic bacterial communities obtained through culture dependent and culture independent approach mingled with polyphasic taxonomic methods. The novel species of methanogens and methanotrophic bacterial communities have been isolated from different ecosystems and characterized for diverse biotechnological applications. To name a few, Methylobacterium phyllosphaerae sp. nov., Methanococcus aeolicus sp. nov. and Methylocella silvestris sp. nov. have been isolated from paddy field, marine environment and forest ecosystem respectively. The present review deals with biodiversity of novel species of methanogens and methanotrophs and their impact on environment.

Isolation, Characterization, and Optimization of Protease‑Producing Bacterium Bacillus thuringiensis from Paddy Field Soil

Background: The ubiquitous proteases that are commonly found in all living organisms play an important role in cell growth and cell differentiation. The bacterium Bacillus thuringiensis (Bt) produces delta-endotoxins that exhibit toxic properties against various insecticides and has demonstrated its potency and safety as a biopesticide agent for decades. The Bt protein includes vegetative, insecticidal, and crystal proteins that exhibit highly toxicants against immature insects (larvae). Objectives: The aim of this research was to use Bt as an alternative to chemical insecticides, and the source of Bt genes aids in the development of a resistant transgenic plant that improves not only productivity but also shift life. Materials and Methods: In the present study, bacterium Bt was isolated from various paddy files around the Hunsur region, Karnataka. The isolated bacteria show a potent protease activity on skim agar plates. Morphology, colony assay, and biochemical characterization were performed for the characteristic properties of bacteria. Further, 16S ribosomal RNA partial sequencing was carried out to identify the specific species of Bacillus. Results: Among nine samples from different paddy soils, three Bacillus isolates SAL-P1, SAL-P2, and SAL-P3 are the major dominant colonies which were streaked onto the fresh skim milk agar plates, out of which SAL-Pl shows an abundant growth and production of an enzyme at pH 7.0, 37°C, and 48 h, respectively. The study also shows the optimum condition of temperature, carbon, nitrogen source, pH for growth, as well as for biomass production. Conclusion: The results of this study confirm the significance of continuous exploration of new Bt strains from different ecological regions that could be more useful for Bt-based bioformulations and the generation of transgenic plants. Furthermore, the growth and biomass production of Btg (isolated from paddy soil) and Bti (reference strain) were found to be identical.

Soil-to-plant transfer factors of 238U and 232Th in rice from Ezillo paddy fields, Ebonyi State, Nigeria

The uptake of radionuclides by plants and their subsequent relocation to the human body through ingestion is one major pathway of human internal exposure. Thus, the present study was conducted to examine the levels of natural radionuclides, 238U and 232Th, in soil of Ezillo paddy fields (field 1 and field 2) at depths 0–4 cm and 4-8 cm, their transfer and accumulation in rice grains. The mean concentrations of both radionuclides in the soil were clearly greater than the UNSCEAR estimated worldwide average while that of the rice with values of 11.7 ± 4.3 and 3.0 ± 1.3 Bq/kg in field 1 and 8.5 ± 4.2 and 4.3 ± 1.6 Bq/kg in field 2 for 238U and 232Th respectively, were well below the worldwide average. The radionuclide transfer factors (TFs) across both depths ranged from 0.03 to 0.67 and 0.01 to 1.20 for 238U and 232Th respectively. The overall geometric means and geometric standard deviations of the TF estimated in field 1 were respectively 0.22 and 1.52 for 238U and 0.18 and 4.21 for 232Th (soil,0-4cm); 0.43 and 1.80 for 238U and 0.18 and 3.79 for 232Th (soil,4-8cm) whereas in field 2 the values were respectively 0.12 and 2.62 for 238U and 0.06 and 4.15 for 232Th (soil,0–4cm); 0.11 and 1.85 for 238U and 0.12 and 4.15 for 232Th (soil,4-8cm). The nuclide concentrations in the rice and the present TFs are within the ranges of values in the literature.

Effects of Superparamagnetic Nanomaterials on Soil Microorganisms and Enzymes in Cadmium-Contaminated Paddy Fields

Using Fe3O4 and hydroxyapatite as raw materials, superparamagnetic nanometer-sized Fe3O4-phosphate functionalized materials (MFH) were prepared. Soil was subsequently magnetically repaired by adding MFH to cadmium-contaminated paddy field soil. Two kinds of rice with high (Yuzhenxiang) and low (Xiangwanxian-13) cadmium enrichment were selected for conduct pot experiments to study the effect of MFH magnetic separation on soil microorganisms and enzymes, and explore the possibility of application in the remediation of cadmium-polluted farmland. The results showed that MFH application improved the soil remediation effect, with significantly reduced total Cd (38.9%) and available Cd (27.3%) contents. In addition, the Cd content of the two kinds of rice grain was significantly reduced. After MFH magnetic separation, soil microbial community diversity and richness were decreased during the jointing, heading, and maturing stages of the two rice varieties. Treatment of cultivated Yuzhenxiang rice with high concentrations of Cd significantly increased the abundance of dominant Firmicute bacteria in the rice field during the jointing and heading stages. With the use of MFH in the magnetic separation, urease, catalase, and soil peroxidase activity were improved during the jointing, heading, and maturing stages of the two rice soils. The POD enzyme activity in the soil planted with Yuzhenxiang was slightly higher than that planted with Xiangwanxian-13, while urease activity showed the opposite trend.

Top-down effects of protists are greater than bottom-up effects of fertilisers on the formation of bacterial communities in a paddy field soil

Communities at any trophic level along the food chain are determined by simultaneous top-down (predators) and bottom-up (nutrients) effects; however, we still lack an understanding of this concept in the soil ecosystem. Here, we aimed to reveal the contributions of the top-down and bottom-up factors on the formation of paddy field bacterial communities. The position of an indigenous bacterial community at the trophic level was centred between soil nutrients (chemical and organic fertilisers [CF and OF, respectively], i.e., bottom-up factors) and bacterial predators (phagotrophic protists, i.e., top-down factors) in a paddy field soil. A 16S rRNA gene amplicon sequencing method was used to evaluate the top-down and bottom-up effects on the bacterial community composition. The results showed that the top-down effects of protists were greater than the bottom-up effects of the applied fertilisers on the formation of bacterial communities. The presence of protists caused the formation of a distinct bacterial community by affecting several bacterial species mainly belonging to Proteobacteria and Bacteroidetes. Among the bottom-up factors, OF significantly affected the bacterial beta diversity, while CF did not. The numbers of bioindicator genera that were associated with the top-down factors were 4.4 and 3.7 times higher than those associated with the bottom effects of CF and OF, respectively. Overall, we provided unique information on the importance of protists in regulating bacterial communities in paddy field soil, which is likely to affect bacterial activities and agricultural productivity.

Enhancement of the nitrogen-fixing activity of paddy soils owing to iron application

ABSTRACT Anaeromyxobacter and Geobacter, iron-reducing bacteria belonging to Deltaproteobacteria, are newly discovered nitrogen-fixing bacteria predominant in paddy soils. We hypothesized that adding ferric iron oxide as an electron acceptor for respiration of the iron-reducing bacteria could enhance the nitrogen-fixing activity of Anaeromyxobacter and Geobacter in paddy soils. In the soil microcosm study, soil nitrogen-fixing activity significantly increased after adding ferrihydrite or Fe2O3, ferric iron oxides, to the soil. In these soils, gene transcripts of nifD from Anaeromyxobacter and Geobacter were detected, whereas those from other general diazotrophs were not detected. Anaeromyxobacter and Geobacter might be involved in the enhanced soil nitrogen-fixing activity. The application of iron powder to paddy field soils also enhanced the soil nitrogen-fixing activity. This study is the first to demonstrate that addition of iron compounds to paddy soil enhanced the soil nitrogen-fixing activity. The results of this study may lead to the development of novel paddy soil management strategies to increase soil nitrogen fertility and ensure rice yields with a reduced nitrogen fertilizer input and a lower environmental nitrogen burden.

Intercropping perennial aquatic plants with rice improved paddy field soil microbial biomass, biomass carbon and biomass nitrogen to facilitate soil sustainability

Agricultural intensification threatens the sustainability of agricultural and environmental quality by decreasing soil quality, reducing biodiversity, and increasing the risk of pest outbreaks. Intercropping has been developed, applied and practiced across the world over centuries, and it has been proven an effective way to increase plant community diversity, thus promoting both complementary and facilitative interactions among species. Here we conducted field experiments from August 2016 to November 2018. We used four important perennial plant species (e.g., Acorus calamus L., Canna indica L., Pontederia cordata L., Thalia dealbata Fraser) to monocrop and intercrop with rice and evaluate their effects on soil physicochemical and biological properties. Our results suggested that soils planted with A. calamus and T. dealbata led to higher total organic carbon (TOC, p < 0.001), total nitrogen (TN), dissolved organic carbon (DOC), moisture content (p = 0.019), and lower soil bulk density (SBD) compared with rice monocropping. Specifically, soil TOC, TN and moisture content in the A. calamus and T. dealbata monocropping systems were, 29.30 and 25.39 %, 15.41 and 25.38 %, and 12.12 and 23.08 % respectively higher than that in the rice monocropping system. We also observed significantly higher microbial biomass (p < 0.001), biomass carbon (p = 0.017), and biomass nitrogen (p < 0.001) and microbial diversity in A. calamus and T. dealbata monocropping and/or intercropping systems. Our results suggest that intercropping perennial plants, A. calamus and/or T. dealbata, in paddy fields for three years could significantly improve soil properties, concomitantly providing more beneficial habitats for microbes, and together, soil sustainability was complemented.

Soil fertility evaluation of rice soils of Lumbajong block of Karbi Anglong district under hill zone of Assam through nutrient indexing

The Lumbajong block of Karbi Anglong district of Assam is characterized by undulating topography comprising of hillocks and lowland paddy fields. Cultivation of rice in traditional ways for years without adequate and balanced use of chemical fertilizers and with little or no use of organic manure have caused severe fertility deterioration resulting in stagnating or even declining productivity of the paddy field soils. Spatial distributions for organic carbon, available N, available P and available K were examined in the soil samples of selected rice fields in 102 different locations covering six villages in the block to evaluate the fertility status of the block. The study revealed that there is much variation in soil fertility status of soils developed on various land forms in the area as the soils were having low to high in organic carbon (0.42 to1.12 %), low to medium in available nitrogen (175.62 to 376 kg/ha) content; low in available P (3.86 to 28.29 kg/ha) and low to high in available K (71.68 – 439.04 kg/ha) contents. The soils of Lumbajong block were characterized as medium-medium-low-medium (MMLM) category based on the nutrient index calculated with respect to organic carbon, available N, available P and available K.

Effect of protists on rhizobacterial community composition and rice plant growth in a biochar amended soil

The effects of protists on an indigenous soil bacterial community, putative bacterial genes involved in N-cycling, and the rice plant growth were studied in poultry litter biochar (PL) and rice husk biochar (RH) amended (with two application doses: 2% and 4% w/w) paddy field soil. The bacterial community composition, which was evaluated using 16S rRNA gene amplicon sequencing, was significantly and differentially affected by the protists, the PL and the RH. The effects of protists on the bacterial community composition were decreased by the RH and the PL treatments. The number of protist-affected bioindicator bacterial taxa was decreased from 90 to 46, 29, 43, and 21 in the 2% RH-, 4% RH-, 2% PL-, and 4% PL-treated soils, respectively. The presence of the protist significantly increased the abundance of the putative bacterial genes involved in mineralisation, dissimilatory nitrate reduction to ammonium (DNRA), and NO3- assimilation, and the same occurred with PL treatments. The rice plant growth and N uptake were always higher in the presence of protists and PL amendments. Overall our results suggest a new insight into the effects of biochar on the bacterial community via altering the trophic interactions.

Assessment of Heavy Metal Pollution Using the Geo-accumulation Index (I-Geo), Pollution Load Index (PLI) and Potential Ecological Risk Index (RI) in Paddy Field Soils Adjacent to Ultrabasic Soils

Assessment of Heavy Metal Pollution Using the Geo-accumulation Index (I-Geo), Pollution Load Index (PLI) and Potential Ecological Risk Index (RI) in Paddy Field Soils Adjacent to Ultrabasic Soils

Assessment of Heavy Metal Pollution Using the Geo-accumulation Index (I-Geo), Pollution Load Index (PLI) and Potential Ecological Risk Index (RI) in Paddy Field Soils Adjacent to Ultrabasic Soils

The content of heavy metals was appraised at paddy fields, from a total of 54 soil samples gathered from two locations in Ranau, Sabah and one from the UKM experimental paddy plot in Peninsular Malaysia, during2014 and 2015. Through an appraisal evaluate of contamination using the Index of Geo-accumulation (I geo) it was noted that Chromium and Nickel levels in Ranau field 1 came under grade 6 (I-geo &gt; 5 is considered to be very contaminated), showing that the soil was heavily tainted with Cr and Ni, whilst Cobalt was discovered to be at the grade 3 level (medium to strong contamination). On the other hand, Ranau field 2's I-geo for other metals came under grade 1(which means medium to no contamination), highlighting the fact that the soils in these areas were tainted with the examined metals, while the control field was found to be grade 0 (no contamination). Ranau field 1 showed strong levels of the contamination factor (CF) for Co, Cr, and Ni, and its Pollution Load Index was(PLI) was&gt; 1, denoting a steady degradation in the area, with high levels of pollution compared to those in the other tested areas. The average monomial ecological risk for Ni was found to be between (40 – 80), highlighting that Ni contamination was considered to be of medium danger to the surrounding environment. Through the Potential Ecological Risk Index, it was seen that Ni was a likely hazard and presented a substantial danger. The RI values for the test sites were as follows: season 2015 (2.89) &lt; control for season 2014 (3.18).

Influence of alternate wetting and drying water-saving irrigation practice on the dynamics of Gallionella-related iron-oxidizing bacterial community in paddy field soil

The redox cycle of iron (Fe) is a key process in the biogeochemistry of paddy field soil. It has been recently remarked that Fe(II)-oxidizing bacteria belonging to the family Gallionellaceae (Gallionella-related FeOB) are one of the key players in the Fe(II) oxidation in the soil. The present study aimed to investigate the influence of alternate wetting and drying (AWD) irrigation for water-saving rice cultivation on the dynamics of the community of Gallionella-related FeOB in the paddy field soil over three seasons (wet-dry-wet seasons) of rice cultivation. The AWD irrigation brought about the reduction of Fe(II) contents in the soil, compared with the continuously flooding (CF) irrigation, especially in the last half of the rice cultivation period in the dry season. In contrast, a trend of higher copy number of 16S rRNA genes of Gallionella-related FeOB was observed in the last half of the rice cultivation period of the AWD paddy soil. As a result, a significant negative correlation was observed between the Fe(II) contents and the copy numbers of 16S rRNA genes. PCR-DGGE analysis of 16S rRNA genes of Gallionella-related FeOB showed that the band patterns were different between the CF and AWD paddy soils. Meanwhile, the results of clone library analysis indicated that differences in the taxonomic composition of Gallionella-related FeOB were not observed between the CF and AWD paddy soils, suggesting that Gallionella-related FeOB responded to the AWD water-saving irrigation on the individual strain levels. The potential of Fe(II)-oxidizing activity and its apparent contribution of the activity of Gallionella-related FeOB to the Fe(II) oxidation in the soil of the investigated field were estimated to be 2.4 × 10−3 to 1.7 × 10−1 mg Fe(II) g−1 dry soil day−1 and 4.6%, respectively, based on the reported Fe(II) oxidation rates of cells. The present study showed that the fluctuation of the redox status of Fe caused by the repeated cycle of wetting and drying of the field brought about the changes in the community structure of Gallionella-related FeOB in the soil. Furthermore, it was suggested that Gallionella-related FeOB were certainly involved in the Fe(II)-oxidizing process in the AWD paddy field soil.

An iron corrosion-assisted H2-supplying system: a culture method for methanogens and acetogens under low H2 pressures

H2 is an important fermentation intermediate in anaerobic environments. Although H2 occurs at very low partial pressures in the environments, the culture and isolation of H2-utilizing microorganisms is usually carried out under very high H2 pressures, which might have hampered the discovery and understanding of microorganisms adapting to low H2 environments. Here we constructed a culture system designated the “iron corrosion-assisted H2-supplying (iCH) system” by connecting the gas phases of two vials (one for the iron corrosion reaction and the other for culturing microorganisms) to achieve cultures of microorganisms under low H2 pressures. We conducted enrichment cultures for methanogens and acetogens using rice paddy field soil as the microbial source. In the enrichment culture of methanogens under canonical high H2 pressures, only Methanobacterium spp. were enriched. By contrast, Methanocella spp. and Methanoculleus spp., methanogens adapting to low H2 pressures, were specifically enriched in the iCH cultures. We also observed selective enrichment of acetogen species by the iCH system (Acetobacterium spp. and Sporomusa spp.), whereas Clostridium spp. predominated in the high H2 cultures. These results demonstrate that the iCH system facilitates culture of anaerobic microorganisms under low H2 pressures, which will enable the selective culture of microorganisms adapting to low H2 environments.

Microbial Methane Production-Oxidation Profile in the Soil of Mangrove and Paddy Fields of West Bengal, India

A comparative vertical profile was performed regarding methane production, methanogenic population, methane oxidation and methanotrophic population in the soil of Sundarban mangrove forest, a paddy field at Namkhana (near to Sundarban mangrove) and a paddy field at Burdwan (non-mangrove region) during pre-monsoon, monsoon and post-monsoon along with selected physicochemical parameters. Maximum methane production rate (8.70 mmol m−2 day−1) was found from the soil collected from 60 cm depth from the paddy field of Burdwan which was 1.42 and 1.79 times higher than that of Sundarban mangrove forest and paddy field of Namkhana, respectively. However maximum methane oxidation rate (3.30 mmol m−2 day−1) was found from the surface soil of Sundarban mangrove forest during monsoon season which was 1.25 and 2.70 times higher than that of paddy field of Namkhana and Burdwan, respectively. An increasing vertical trend was found for the ratio of methanogenic population to methanotrophic population and Methane production rate to methane oxidation rate for the studied stations suggested dominance of methanogens in the deeper soil. Both those two ratios were maximum for paddy field of Burdwan suggested maximum methane flux from this station than other two stations due to presence of a smaller number of methanotrophic bacteria. All three stations showed significant correlation between methane production with methanogenic population and methane oxidation with methanotrophic population throughout the year suggested major microbial contribution in the net flux of methane from the soil.