Rice Serine Hydroxymethyltransferases: Evolution, Subcellular Localization, Function and Perspectives.

In rice, there is a lack of comprehensive research on the functional aspects of the members of the serine hydroxymethyltransferase (SHMT) gene family. This study provides a comprehensive investigation of the SHMT gene family, covering phylogeny, gene structure, promoter analysis, expression analysis, subcellular localization, and protein interaction. Remarkably, we discovered a specific gene loss event occurred in the chloroplast-localized group IIa SHMTs in monocotyledons. However, OsSHMT3, which originally classified within cytoplasmic-localized group Ib, was found to be situated within chloroplasts in rice protoplasts. All five OsSHMTs are capable of forming homodimers, with OsSHMT3 being the only one able to form dimers with other OsSHMTs, except for OsSHMT1. It is proposed that OsSHMT3 functions as a mobile protein, collaborating with other OsSHMT proteins. Furthermore, the results of cis-acting element prediction and expression analysis suggested that members of the OsSHMT family could be involved in diverse stress responses and hormone regulation. Our study aims to provide novel insights for the future exploration of SHMTs.

Purification effect and microbial community structure of bio filter on rural dispersed sewage.

Taking rural dispersed sewage for research objects, the treatment effect and microbial community structure characteristics of a bio filter (BF) reactor was studied. At fixed time and location, the removal efficiencies of common pollutants were investigated. By using high-throughput sequencing method, the heterogeneities of microbial community structure in fillers and plant roots were analyzed. The results showed that the average annual removal rates of CODCr, NH3-N, TN, and TP by the BF were 83.10 %, 65.67 %, 60.25 %, and 80.32 % respectively, and the effluent could reach the first grade of the water pollutant discharge standard of rural sewage treatment facility (DB51/2626-2019). During the sewage treatment process, Scindapsus could effectively establish complex and stable microbial communities, and could better degrade pollutants, especially nitrogen removal. The dominant microbial communities were more than 11 phyla and 19 classes. At the genus level, the dominant bacteria included Nitrospira, Arthrobacter, Rhodoplanes, etc.

Optimization pilot scale study on ammonia nitrogen removal by bio filter.

In order to obtain the optimal conditions for ammonia nitrogen (AN) wastewater treatment by bio filter (BF), the effects of ratio of carbon to nitrogen (C/N), pH, and hydraulic load (HL) on the AN degradation were studied by Response Surface Methodology (RSM). Central Composite Design (CCD) experiments were conducted, and the response of the AN removal rates were fitted to a second-order polynomial model. The analysis of variance showed that the model was accurate and reliable. Through model fitting, the optimal condition for AN removal was: C/N of 18.95, pH of 7.78, and HL of 1.04 d-1. The maximum AN removal rate predicted by the model was 91.90%, accorded with the experimental verification value of 91.37% under the optimal condition. The research provided valuable demonstration for optimizing process parameters on AN removal in BF.

Mineralization of phenanthrene sorbed on multiwalled carbon nanotubes.

Carbon nanotubes have attracted attention around the world because of their high sorption capacity for hydrophobic organic compounds (HOCs); however, the bioavailability of HOCs sorbed on carbon nanotubes to bacteria is not well known. In the present study, (14) C-labeled and unlabeled phenanthrene was spiked onto four kinds of multiwalled carbon nanotubes (MWCNTs) and aged for 60 d, and the mineralization of phenanthrene sorbed on MWCNTs was studied. The mineralization efficiencies of phenanthrene sorbed on the four kinds of MWCNTs were 2.38, 8.84, 23.88, and 31.47%, respectively, after incubation for 35 d, which were positively correlated with the sum of fast and slow desorption fractions of phenanthrene (p < 0.05). The authors found that the mineralization efficiencies agreed well with the MWCNT properties; the increasing specific surface area and mesopore and micropore volume of MWCNTs caused a significant decrease in the mineralization efficiency of phenanthrene (p < 0.05). After incubation for 35 d, the density of bacteria had a significant positive correlation with both the desorption and the mineralization efficiencies. The authors inferred that, although MWCNTs might have toxic effects on the bacteria, the biodegrading ability of bacteria might not decrease significantly under the influence of MWCNTs with low surface area.

Effects of suspended sediment on the biodegradation and mineralization of phenanthrene in river water.

High suspended sediment (SPS) concentration commonly exists in many Asian rivers. Furthermore, climate change can cause high floods and lead to the resuspension of sediments and soil erosion, resulting in high SPS concentration in many natural waters. This research studied the impact of the presence of SPS and organic C composition of SPS on the biodegradation and mineralization of phenanthrene (PHE). Three sediments, including original sediment (OS), 375 degrees C (S375), and 600 degrees C (S600) combusted sediment, were studied. A flask-based 14C-respirometer system was applied to study the mineralization of [14C]PHE by Agrobacterium sp. The mineralization rate of PHE in the absence of SPS was significantly lower than that with the presence of OS and S600 but higher than that with S375, suggesting that the effect of the presence of sediment on PHE mineralization depended on its organic C composition. The residual levels of PHE in the S375 and OS systems were about 1.5 times that of the S600 system after incubation for 2 d. After 26-d incubation, the mineralization rates of PHE were 34.64, 29.40, and 14.00% in the OS, S600, and S375 systems, respectively. The first-order rate constants of the OS and S600 systems were about three times that of the S375 system. The net influence of SPS on the biodegradation and mineralization rates of PHE was dependent on its effects on compound bioavailability and bacteria population. This study suggested that black C played a key role in reducing the mineralization rates of PHE in sediments-even without aging.

Levels of arsenic and heavy metals in the rural soils of Beijing and their changes over the last two decades (1985-2008).

Heavy metal levels in the rural soils are associated with the quality of agricultural products. In this study, soil samples were collected from the rural soils of Beijing; distribution of As, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, Zn and their changes over the last two decades have been investigated. The results indicated that the concentrations of Co, Cr, Mn, Ni, and V were primarily controlled by the parent materials of soils, while concentrations of Hg, As, Cu, Pb, and Zn were affected by anthropogenic activities. Hg concentration in the surface soils was 2-3 times the subsurface soils; slight accumulations of As, Cu, Pb, and Zn in the top soils were also observed. The bioavailable fractions of heavy metals including exchangeable and carbonate-bounded fraction were lower than 10% except for Cr, Mn and Zn. In general, the concentrations of heavy metals in the rural soils of Beijing met environmental quality standard (grade II) for soils of China. Although some elements such as Hg and As have increased significantly in several sample sites, the average concentrations of all heavy metals had no significant change over the past 20 years due to effective environmental protection for many years in Beijing.