Bacterial biogeography in China and its association to land use and soil organic carbon

●6102 high-quality sequencing results of soil bacterial samples were re-analyzed.●The type of land use was the principal driver of bacterial richness and diversity.●SOC content is positively correlated with key bacteria and total nitrogen content.Soil organic carbon(SOC)is the largest pool of carbon in terrestrial ecosystems and plays a crucial role in regulating atmospheric CO_(2) concentrations.Identifying the essential relationship between soil bacterial communities and SOC concentration is complicated because of many factors,one of which is geography.We systematically re-analyzed 6102 high-quality bacterial samples in China to delineate the bacterial biogeographic distribution of bacterial communities and identify key species associated with SOC concentration at the continental scale.The type of land use was the principal driver of bacterial richness and diversity,and we used machine learning to calculate its influence on microbial composition and their co-occurrence relationship with SOC concentration.Cultivated land was much more complex than forest,grassland,wetland and wasteland,with high SOC concentrations tending to enrich bacteria such as Rubrobacter,Terrimonas and Sphingomona.SOC concentration was positively correlated with the amounts of soil total nitrogen and key bacteria Xanthobacteraceae,Streptomyces and Acidobacteria but was negatively correlated with soil pH,total phosphorus and Micrococcaceae.Our study combined the SOC pool with bacteria and indicated that specific bacteria may be key factors affecting SOC concentration,forcing us to think about microbial communities associated with climate change in a new way.

The mechanism of different cyanobacterial responses to glyphosate

Glyphosate, the most extensively used herbicide globally, has raised ecotoxicological concerns because it can be transported into the aquatic environment and cause adverse effects on the aquatic system. However, the functional mechanism of glyphosate on cyanobacteria are not completely disentangled. In this study, we selected six common cyanobacteria to evaluate glyphosate effects on cyanobacterial growth in monoculture experiment. Results showed that the growth of five tested cyanobacterial species were promoted under different degrees, and only Pseudanabaena was inhibited by glyphosate. In the phylogenetic tree based on gene sequences of 5-enol-pyruvylshikimate-3-phosphate synthase(EPSPS),a target for glyphosate, we found that the position of Pseudanabaena is the closest to plant,which was sensitive to glyphosate, thereby explaining the inhibitory effect of Pseudanabaena following glyphosate exposure. The primary degraded metabolites or analogs did not induce cyanobacterial growth, laterally demonstrating that glyphosate was used as a source of phosphorus to accelerate cyanobacterial growth because phosphorus levels increased in the medium of glyphosate treatment. Overall, this study provides a better understanding of the influence of glyphosate on the composition of aquatic microbiota and explains the mechanism of cyanobacterial response to glyphosate.

Assessment of residual chlorine in soil microbial community using metagenomics

Chlorine-containing disinfectants have been widely used around the world for the prevention and control of the COVID-19 pandemic.However,at present,little is known about the impact of residual chlorine on the soil micro-ecological environment.Herein,we treated an experimental soil-plant-microbiome microcosm system by continuous irrigation with a low concentration of chlorine-containing water,and then analyzed the influence on the soil microbial community using metagenomics.After 14-d continuous chlorine treatment,there were no significant lasting effect on soil microbial community diversity and composition either in the rhizosphere or in bulk soil.Although metabolic functions of the rhizosphere microbial community were affected slightly by continuous chlorine treatment,it recovered to the original status.The abundance of several resistance genes changed by 7 d and recovered by 14 d.According to our results,the chlorine residue resulting from daily disinfection may present a slight long-term effect on plant growth(shoot length and fresh weight)and soil micro-ecology.In general,our study assisted with environmental risk assessments relating to the application of chlorine-containing disinfectants and minimization of risks to the environment during disease control,such as COVID-19.

High strength and ductility Mg-8Gd-3Y-0.5Zr alloy with bimodal structure and nano-precipitates

To resolve the strength-ductility trade-off problem for high-strength Mg alloys,we prepared a high performance Mg-8Gd-3Y-0.5 Zr(wt%)alloy with yield strength of 371 MPa,ultimate tensile strength of 419MPa and elongation of 15.8%.The processing route involves extrusion,pre-deformation and aging,which leads to a bimodal structure and nano-precipitates.Back-stress originated from the deformationincompatibility in the bimodal-structure alloy can improve ductility.In addition,dislocation density in coarse grains increased during the pre-deformation strain of 2%,and the dislocations in coarse grains can promote the formation of chain-like nano-precipitates during aging treatment.The chain-like nanoprecipitates can act as barriers for dislocations slip and the existing mobile dislocations enable good ductility.

Cyclic shear deformation and fatigue of extruded Mg-Gd-Y magnesium alloy

Deformation and fatigue of extruded Mg-8.0 Gd-3.0 Y-0.5 Zr(GW83, wt%) magnesium(Mg) alloy were experimentally investigated under cyclic torsion using tubular specimen fabricated along the extrusion direction. The controlled shear strain amplitudes ranged from 0.606% to 4.157%. Twinning and detwinning of extension twins are observed to take place during cyclic torsion and the shear stress-shear strain hysteresis loops display a perfectly symmetric shape at all tested strain amplitudes. Marginal cyclic softening is observed when the shear strain amplitude is higher than 1.732%. The strain-life fatigue curve shows two kink points, corresponding to the shear strain amplitude of 1.040% and 1.732%, respectively.When the shear strain amplitude is higher than the upper kink point, early fatigue crack is found to initiate on the maximum shear plane. When the strain amplitude is lower than the lower kink point,fatigue cracking is parallel to the maximum tensile plane. At an identical equivalent strain amplitude,the fatigue life under pure shear is much higher than that under tension-compression. The fatigue life of extruded GW83 alloy is much higher than that of extruded AZ31 B alloy at the same plastic strain energy density.

Alteration of dominant cyanobacteria in different bloom periods caused by abiotic factors and species interactions

Freshwater cyanobacterial blooms have drawn public attention because they threaten the safety of water resources and human health worldwide.Heavy cyanobacterial blooms outbreak in Lake Taihu in summer annually and vanish in other months.To find out the factors impacting the cyanobacterial blooms,the present study measured the physicochemical parameters of water and investigated the composition of microbial community using the 16S rRNA gene and internal transcribed spacer amplicon sequencing in the months with or without bloom.The most interesting finding is that two major cyanobacteria,Planktothrix and Microcystis,dramatically alternated during a cyanobacterial bloom in 2016,which is less mentioned in previous studies.When the temperature of the water began increasing in July,Planktothrix appeared first and showed as a superior competitor for M.aeruginosa in NO3^−-rich conditions.Microcystis became the dominant genus when the water temperature increased further in August.Laboratory experiments confirmed the influence of temperature and the total dissolved nitrogen(TDN)form on the growth of Planktothrix and Microcystis in a co-culture system.Besides,species interactions between cyanobacteria and non-cyanobacterial microorganisms,especially the prokaryotes,also played a key role in the alteration of Planktothrix and Microcystis.The present study exhibited the alteration of two dominant cyanobacteria in the different bloom periods caused by the temperature,TDN forms as well as the species interactions.These results helped the better understanding of cyanobacterial blooms and the factors which contribute to them.

Pollutant toxicology with respect to microalgae and cyanobacteria

Microalgae and cyanobacteria are fundamental components of aquatic ecosystems.Pollution in aquatic environment is a worldwide problem.Toxicological research on microalgae and cyanobacteria can help to establish a solid foundation for aquatic ecotoxicological assessments.Algae and cyanobacteria occupy a large proportion of the biomass in aquatic environments;thus,their toxicological responses have been investigated extensively.However,the depth of toxic mechanisms and breadth of toxicological investigations need to be improved.While existing pollutants are being discharged into the environment daily,new ones are also being produced continuously.As a result,the phenomenon of water pollution has become unprecedentedly complex.In this review,we summarize the latest findings on five kinds of aquatic pollutants,namely,metals,nanomaterials,pesticides,pharmaceutical and personal care products(PPCPs),and persistent organic pollutants(POPs).Further,we present information on emerging pollutants such as graphene,microplastics,and ionic liquids.Efforts in studying the toxicological effects of pollutants on microalgae and cyanobacteria must be increased in order to better predict the potential risks posed by these materials to aquatic ecosystems as well as human health.

Effects of imazethapyr spraying on plant growth and leaf surface microbial communities in Arabidopsis thaliana

Imazethapyr (IM) is an acetolactate synthase (ALS)-inhibiting herbicide that has been widely used in recent years.However,IM spraying can lead to the accumulation of herbicide residues in leaves.Here,we determined the effects of IM spraying on the plant growth and leaf surface microbial communities of Arabidopsis thaliana after 7 and 14 days of exposure.The results suggested that IM spraying inhibited plant growth.Fresh weight decreased to 48% and 26% of the control value after 7 and 14 days,respectively,of 0.035 kg/ha IM exposure.In addition,anthocyanin content increased 9.2-fold and 37.2-fold relative to the control content after 7 and 14 days of treatment,respectively.Furthermore,IM spraying destroyed the cell structures of the leaves,as evidenced by increases in the number of starch granules and the stomatal closure rate.Reductions in photosynthetic efficiency and antioxidant enzyme activity were observed after IM spraying,especially after 14 days of exposure.The diversity and evenness of the leaf microbiota were not affected by IM treatment,but the composition of community structure at the genus level was altered by IM spraying.Imazethapyr application increased the abundance of Pseudomonas,a genus that includes species pathogenic to plants and humans,indicating that IM potentially increased the abundance of pathogenic bacteria on leaves.Our findings increase our understanding of the relationships between herbicide application and the microbial community structures on plant leaves,and they provide a new perspective for studying the ecological safety of herbicide usage.

Metabolomic modulations in a freshwater microbial community exposed to the fungicide azoxystrobin

An effective broad-spectrum fungicide,azoxystrobin(AZ),has been widely detected in aquatic ecosystems,potentially affecting the growth of aquatic microorganisms.In the present study,the eukaryotic alga Monoraphidium sp.and the cyanobacterium Pseudanabaena sp.were exposed to AZ for 7 days.Our results showed that 0.2–0.5 mg/L concentrations of AZ slightly inhibited the growth of Monoraphidium sp.but stimulated Pseudanabaena sp.growth.Meanwhile,AZ treatment effectively increased the secretion of total organic carbon(TOC)in the culture media of the two species,and this phenomenon was also found in a freshwater microcosm experiment(containing the natural microbial community).We attempted to assess the effect of AZ on the function of aquatic microbial communities through metabolomic analysis and further explore the potential risks of this compound.The metabonomic profiles of the microcosm indicated that the most varied metabolites after AZ treatment were related to the citrate cycle(TCA),fatty acid biosynthesis and purine metabolism.We thereby inferred that the microbial community increased extracellular secretions by adjusting metabolic pathways,which might be a stress response to reduce AZ toxicity.Our results provide an important theoretical basis for further study of fungicide stress responses in aquatic microcosm microbial communities,as well as a good start for further explorations of AZ detoxification mechanisms,which will be valuable for the evaluation of AZ environmental risk.

Abundance cannot represent antibiotic resistance risk

Antibiotic resistance is increasing in the soil environments(Chen et al.,2019a;Zhu et al.,2019)and transferring into human body via plant microbiome,which can be exacerbated by the food chain,direct contact pathway,and globalization process(Chen et al.,2019b).