Effects of straw return and aeration on oxygen status and redox environment in flooded soil

To study the effects of straw return and aeration of the water layer on oxygen and redox status in the water column and at different depths in paddy field soil, a short-term incubation experiment was conducted with four treatments: (1) no straw return (NS); (2) straw return without aeration (S); (3) straw return and 30 minutes of aeration per day (SO30); and (4) straw return and 90 minutes of aeration per day (SO90). Compared to NS, S decreased dissolved oxygen (DO) and redox potential (ORP) by 23–58% and 47–53 mV, respectively, and increased active reducing substance (ARS) by 21–46% in the water and soil layers. The aeration treatments increased DO and ORP by 25–120% and 11–86 mV, respectively, and reduced ARS by 5–16% compared to S. The results indicated that straw return to paddy fields exacerbated hypoxia and reducing conditions in the soil. SO90 achieved better effects than SO30 in alleviating the negative impact of straw return by supplying more oxygen, but the effects weakened over time and with soil depth.

Response of methanogen communities to the elevation of cathode potentials in bioelectrochemical reactors amended with magnetite

Electromethanogenesis refers to the process where methanogens utilize current for the reduction of CO 2 to CH 4 . Setting low cathode potentials is essential for this process. In this study, we test if magnetite, an iron oxide mineral widespread in the environment, can facilitate the adaption of methanogen communities to the elevation of cathode potentials in electrochemical reactors. Two-chamber electrochemical reactors were constructed with inoculants obtained from paddy field soil. We elevated cathode potentials stepwise from the initial -0.6 V vs the standard hydrogen electrode (SHE) to -0.5 V and then to -0.4 V over the 130 days acclimation. Only weak current consumption and CH 4 production were observed in the bioreactors without magnetite. But significant current consumption and CH 4 production were recorded in the magnetite bioreactors. The robustness of electro-activity of the magnetite bioreactors was not affected by the elevation of cathode potentials from -0.6 V to -0.4 V. But, the current consumption and CH 4 production were halted in the bioreactors without magnetite when the cathode potentials were elevated to -0.4 V. Methanogens related to Methanospirillum were enriched on the cathode surfaces of magnetite bioreactors at -0.4 V, while Methanosarcina relatively dominated in the bioreactors without magnetite. Methanobacterium also increased in the magnetite bioreactors but stayed off electrodes at -0.4 V. Apparently, the magnetite greatly facilitates the development of biocathodes, and it appears that with the aid of magnetite, Methanospirillum spp. can adapt to the high cathode potentials performing efficient electromethanogenesis. IMPORTANCE Converting CO 2 to CH 4 through bioelectrochemistry is a promising approach to the development of green energy biotechnology. This process however requires low cathode potentials, which takes cost. In this study, we test if magnetite, a conductive iron mineral, can facilitate the adaption of methanogens to the elevation of cathode potentials. In the two-chamber reactors constructed by using inoculants obtained from paddy field soil, biocathodes were firmly developed in the presence of magnetite, whereas only weak activities in CH 4 production and current consumption were observed in the bioreactors without magnetite. The elevation of cathode potentials did not affect the robustness of electro-activity of the magnetite bioreactors over the 130 days acclimation. Methanospirillum were identified as the key methanogens associated with the cathode surfaces during the operation at high potentials. The findings reported in this study shed new light on the adaption of methanogen communities to the elevated cathode potentials in the presence of magnetite.

​Diversity of Non-heterocystous Cyanobacteria in Paddy Field Soil

Paddy field soil is a natural habitat for many Cyanobacteria. Generally Heterocystous form dominate the nitrogen deficient soil. Non-heterocystous forms are also known to fix nitrogen. The diversity and the distribution of these forms vary. 20 Soil samples were serial diluted in BG-11 devoid of nitrogen supplement. Later the colonies were streaked to obtain axenic culture. The soil pH was also determined to study the effect on the diversity. The relative abundance of the BGA species was determined .Diversity of non-heterocystous form in the paddy field was found to be dominated by filamentous BGA, Lynbgya by 21%, Oscillatoria and Phormidium by 17% and colonial form Chrococcus sp by 12.5% Followed by Myxosarcina sp., 8%, while Aphanocapsa sp., Chlorogloea sp., Crinaluim sp., Gleocapsa sp, Plectonema sp. and Schizothrix sp., were 4%. A majority of the non-heterocystous BGA were found in the soil which had a pH ranging between 8.2-8.6. Diversity study of non-heterocystous BGA can help in understanding the distribution and further aid in the study of nitrogen fixation in these forms.

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

Ferrigenium kumadai An22 T (=JCM 30584 T =NBRC 112974 T =ATCC TSD-51 T ) 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 An22 T , which was obtained from the hybrid data of Oxford Nanopore long-read and Illumina short-read sequencing.

Biodegradation of Di-(2-ethylhexyl) Phthalate by Novel Rhodococcus Aetherivorans PFS1 Strain Isolated From Paddy Field Soil

Di-(2-ethylhexyl)-phthalate (DEHP) is the phthalate ester frequently utilized as a plasticizer, commonly found in cosmetics, packaging materials, moreover, it has carcinogenic and mutagenic effect on humans. In the current study, we isolated the soil bacterium Rhodococcus aetherivorans PFS1 and to assess its DEHP degradation ability in various environmental conditions. The strain PFS1 was isolated from paddy field soil and identified by the 16S rRNA sequencing analyses. The strain PFS1 was examined for its biodegradation ability of DEHP at various pH, temperature, salt concentration, glucose concentration, and high and low concentration of DEHP. Moreover, the biodegradation of DEHP at a contaminated soil environment by strain PFS1 was assessed. Further, the metabolic pathway of DEHP degradation by PFS1 was analyzed by HPLC-MS analysis. The results showed that the strain PFS1 effectively degraded the DEHP at neutral pH and temperature 30 °C, moreover, expressed excellent DEHP degradation at the high salt concentration (up to 50 g/L). The strain PFS1 was efficiently degraded the different tested phthalate esters (PAEs) up to 90%. Significantly removed the DEHP contamination in soil along with native organisms which are present in soil up to 94.66%, nevertheless, the PFS1 alone degraded the DEHP up to 87.665% in sterilized soil. According to HPLC-MS analysis, DEHP was degraded into phthalate (PA) by PFS1 strain via mono (2-ethylehxyl) phthalate (MEHP), then PA was utilized for cell growth. These results suggest that R. aetherivorans PFS1 has excellent potential to degrade DEHP at various environmental conditions especially in contaminated paddy field soil.