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Precipitation plays a dominant role in regulating terrestrial carbon fluxes. In concert with global warming, aridity has been increasing during recent decades in most parts of the world. How global terrestrial carbon fluxes respond to this change, however, is still unclear. Using a remote-sensing-driven, process-based model, the Boreal Ecosystem Productivity Simulator (BEPS), this study investigated the responses of global terrestrial carbon fluxes to meteorological drought, which were characterized by the standardized precipitation evapotranspiration index (SPEI). The results showed that the response of terrestrial carbon fluxes to drought exhibited distinguishable spatial heterogeneity. In most regions, terrestrial carbon fluxes responded strongly to drought. With an increase in annual water balance (annual precipitation minus annual potential evapotranspiration), the response of carbon fluxes to drought became weaker. The lagged time of terrestrial carbon fluxes responding to drought decreased with the increasing strength of carbon fluxes in response to drought. The sensitivity of terrestrial carbon fluxes to drought also showed noticeable spatial heterogeneity. With an increase in annual water balance, the sensitivity first increased and then decreased. Terrestrial carbon fluxes exhibited the highest sensitivity to drought in semi-arid areas. [ABSTRACT FROM AUTHOR]

We discuss an algorithm for the autoregression (AR) model as a typical time-series model. By analyzing the structure of the AR model, we highlight the shortcomings of traditional algorithms for model parameter estimation and propose an approach to overcome the shortcomings of traditional solutions for the AR model. The errors-in-variables (EIV) model is used to solve an existing problem. There is an obvious difference between the AR model and a traditional model. For the AR model, one observation datum appears repeatedly; hence, the residual of one observation datum is not unique. Furthermore, in theory, the optimal estimation of model parameters cannot be obtained by current solutions. Based on an analysis of the AR model, we focus on how to obtain the optimal estimation when the observation data of the AR model are contaminated by outliers. The median function is used to establish a modified solution for the AR model based on the institute of geodesy & geophysics, Chinese academy of sciences (IGG) weight function by comparison with current algorithms for the robust estimation of the EIV model. We propose an iterative algorithm based on median function. Finally, we apply two numerical instances to compare the proposed algorithm with traditional algorithms and draw conclusions from results of the instances. [ABSTRACT FROM AUTHOR]

Abstract Biorefinery of biomass-based biofuels and biochemicals by microorganisms is a competitive alternative of traditional petroleum refineries. Zymomonas mobilis is a natural ethanologen with many desirable characteristics, which makes it an ideal industrial microbial biocatalyst for commercial production of desirable bioproducts through metabolic engineering. In this review, we summarize the metabolic engineering progress achieved in Z. mobilis to expand its substrate and product ranges as well as to enhance its robustness against stressful conditions such as inhibitory compounds within the lignocellulosic hydrolysates and slurries. We also discuss a few metabolic engineering strategies that can be applied in Z. mobilis to further develop it as a robust workhorse for economic lignocellulosic bioproducts. In addition, we briefly review the progress of metabolic engineering in Z. mobilis related to the classical synthetic biology cycle of "Design-Build-Test-Learn", as well as the progress and potential to develop Z. mobilis as a model chassis for biorefinery practices in the synthetic biology era. Highlights • Z. mobilis has attractive features for lignocellulosic biofuels and biochemicals. • Progress achieved for expanded substrate utilization and robustness improvement. • Knowledge learned from Z. mobilis can be employed in other microorganisms. • Z. mobilis can be developed as a synthetic chassis. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Chlorella was introduced into MFC for Cd(II) removal in the biocathode. • Simultaneous high power generation and metal removal efficiencies can be achieved. • NF-rGO enhanced power generation (36.4 mW m−2) and Cd(II) removal (115 g m−2). • NF-rGO improve the maximum tolerable concentrations of Cd(II) for algal biocathode. • Cadmium were removed mainly through hydroxide precipitation and biosorption. Abstract Microalgae ( Chlorella sp. QB-102) was introduced into microbial fuel cell (MFC) as the cathode for Cd(II) removal using nickel foam/graphene (NF/rGO) as electrodes. It was found that graphene enhanced the power generation and decreased the internal resistance in the algal-cathode MFC. The start-up time was shortened and the maximum power density obtained by using NF/rGO (36.4 mW m−2) was eight times higher against bare NF. Graphene further improve the maximum tolerable concentrations of Cd(II) in the algal-cathode, which estimated to be 50 ppm. Using NF/rGO electrode, the algal-cathode MFC achieved a high Cd(II) removal efficiency of almost 95% and a maximum adsorption amount of 115 g m−2. It was found that hydroxide precipitation and biosorption are the major mechanisms for the Cd removal in the biocathode self-sustained MFC. The results suggested that photoautographic MFC is feasible and effective for heavy metal removal in the algal-cathode and graphene modification in the electrodes is recommended. [ABSTRACT FROM AUTHOR]

Temperature and light intensity are important environmental factors influencing microalgae for biodiesel production. The aim of present work was to study the effects of temperature (15 °C, 25 °C, and 35 °C) and its combination with high light intensity (HL, 400 μmol photon m −2  s −1 ) on lipid production of Monoraphidium dybowskii Y2 which was isolated from desert. The results demonstrated that algal growth was only inhibited at 15 °C. Promoted lipid content and decreased Fv/Fm were observed in 15 °C and 35 °C. Cellular carbohydrate, protein conversion and membrane lipid (MGDG, DGDG and SQDG) remodeling contributes for lipid accumulation. Stress combined temperatures with HL are benefit for lipid production, especially desired neutral lipid productivity all exceed 40 mg L −1  d −1 . Fatty acids compositions of C16:0 and C18:1 were further promoted under 15 °C or 35 °C combined with HL. Thus, M. dybowskii Y2 will well-adapted to outdoors cultivation for biodiesel production. [ABSTRACT FROM AUTHOR]

Cultivation modes of autotrophic microalgae for biodiesel production utilizing open raceway pond were analyzed in this study. Five before screened good microalgae were tested their lipid productivity and biodiesel quality again in outdoor 1000 L ORP. Then, Chlorella sp. L1 and Monoraphidium dybowskii Y2 were selected due to their stronger environmental adaptability, higher lipid productivity and better biodiesel properties. Further scale up cultivation for two species with batch and semi-continuous culture was conducted. In 40,000 L ORP, higher lipid productivity (5.15 versus 4.06 g m −2 d −1 for Chlorella sp. L1, 5.35 versus 3.00 g m −2 d −1 for M . dybowskii Y2) was achieved in semi-continuous mode. Moreover, the financial costs of 14.18 $ gal −1 and 13.31 $ gal −1 for crude biodiesel in two microalgae with semi-continuous mode were more economically feasible for commercial production on large scale outdoors. [ABSTRACT FROM AUTHOR]

The aim of this study was to optimize the light regimes including initial inoculum density, photoperiod and light intensity on the growth and lipid (TAG) accumulation in Ankistrodesmus fusiformis H1 for biodiesel production. At last, the strategy of 4.47 mM urea with initial OD 680 -0.5, 18:6 h light/dark cycle and 200 μmol photon m −2 s −1 regimes were optimized. The lipid productivity of 116.88 mg L −1 d −1 and 57.58% neutral lipid in total lipid were achieved finally. Moreover, the changes of photosynthetic activity, pigments contents and biochemical compositions revealed that more carbon flow to lipid synthesis. Therefore, A. fusiformis H1 is an ideal candidate for biodiesel production by utilizing light appropriately. [ABSTRACT FROM AUTHOR]

Chlorella sp. and Monoraphidium sp. were the potential microalgal species for lipid production. This study aimed to investigate different light intensities (40, 200, 400 μmol photon m −2 s −1 ) on physiological changes, photosynthetic carbon partitioning and neutral lipid accumulation in both microalgae. Results suggested that under high light (HL, 400 μmol photon m −2 s −1 ), chlorophyll degraded, protein and carbohydrate content decreased; more carbon allocated into lipid as well as most of intracellular space was occupied by lipid bodies. Moreover, with the lipid accumulation, Fv/Fm decreased and ROS scavenging enzyme increased. Membrane lipid reduced dramatic (29.73–37.97%) to format NL (71.66% of total lipid in Chlorella sp. L1 and 60.65% in Monoraphidium dybowskii Y2). The NL productivity under HL (51.36 and 49.71 mg L −1 d −1 ) were more than 3 times of those under LL. Additionally, FAME profiles proved that the useful fatty acid components for biodiesel production were enhanced under HL. [ABSTRACT FROM AUTHOR]

The errors-in-variables (EIV) model is used for data processing in the field of geodesy. However, the EIV model may be ill-posed. By analyzing the decreasing regularization (D-regularization) characteristic of solutions for EIV models, algorithms using traditional methods such as singular value decomposition or the Tikhonov function can directly determine the irrationality of a model. When an EIV model is ill-posed, solutions in which the observation errors in the coefficient matrix are simulated by variables make the ill-posed nature of the model more serious. This is because the simulated observation errors are subtracted from the coefficient matrix in subsequent computations, which reduces the singular value of the normal matrix. This point is verified using an example. To account for the D-regularization of solutions in EIV models, a modified algorithm is derived by classifying the models into two categories, and the regularization parameters are iteratively revised based on the mean squared error. Finally, some conclusions are drawn from two separate examples. [ABSTRACT FROM AUTHOR]

NaCl induction in photoautotrophic two-step cultivation is very promising, but time node and concentration are critical to the entire production. In this study Monoraphidium dybowskii LB50 was subjected to different NaCl concentrations at different growth phases. Results showed that during the initial phase (IP), fixed carbon was used for sugar and lipid under 5 g L −1 NaCl induction, as well as for protein under 10 g L −1 NaCl induction. At late-exponential growth phase (LEGP), the highest lipid productivity was obtained at 20 g L −1 NaCl. At stationary phase (SP) the highest lipid productivity was also under 20 g L −1 NaCl but lower than that of LEGP. In summary, lipid content and quality were improved at all growth phases under NaCl induction. Therefore, cultivation scale can be sued to determine the time node and dosage of the inducer, thereby realizing the economic efficiency of the fundamental guarantee in photoautotrophic two-step cultivation. [ABSTRACT FROM AUTHOR]

The effects of fluctuating intensity of solar radiation on biomass and lipid in oleaginous microalgae are important. However, this topic has not been the subject of studies for a long time. In this study, four oleaginous microalgae from semi-arid areas were screened and cultivated outdoors under different fluctuating intensities. Results showed that the highest lipid productivities and neutral lipid (NL) contents occurred under high fluctuating intensity (HFI), in which 13–20% of the increased NL came from glycolipid transformation without phospholipid conversion. Chlorella sp. L1 and Monoraphidium dybowskii Y2 obtained from biological soil crusts in desert had the largest biomass (137.13, 106.61 mg L −1 d −1 ) and lipid yields (35.06, 32.45 mg L −1 d −1 ) under HFI. The highest areal lipid productivities of 9.06 and 8.95 g m −2 d −1 and better biodiesel quality were observed under HFI. Accordingly, sufficiently adopting fluctuating light intensity outdoors to culture microalgae was an economic and effective approach. [ABSTRACT FROM AUTHOR]

NaCl is an effective inducer of lipid accumulation in freshwater microalgae, but little is known on whether the enhanced lipid components are desired. To address this issue, Monoraphidium dybowskii LB50 from a freshwater habitat was selected, cultivated, and subjected to NaCl induction at different scales outdoors. Results showed that the optimal salt concentration reduced glycolipid (GL) content, as well as enhanced neutral lipid (NL) and phospholipid (PL) contents. Moreover, GL was preferentially converted to NL at 20 g L −1 NaCl. Total lipid and NL contents respectively increased to 41.7% and 17.48% in 1 d. The highest NL productivity was also achieved at both the 5 L (24.13 mg L −1 d −1 ) and 140 L (13.05 mg L −1 d −1 , 3.43 g m −2 d −1 ) scales. These results suggest that NL accumulated effectively and rapidly at different scales, indicating that this strategy has broad application prospects for the scale-up cultivation of oily algae. [ABSTRACT FROM AUTHOR]

High-density culture for microbial lipid preparation from low-cost lignocellulosic feedstocks is crucial for commercial-scale biodiesel production. Herein, fed-batch saccharification of alkaline organosolv pretreatment (AOP) of corn stover at an extremely high solids content of 47% (w/v) released 299.5 g/L of lignocellulosic sugars including 18.3% of soluble oligosaccharides. Three types of liquid hydrolysates for seed culture, fermentation, and feeding during fed-batch culture were obtained from the hydrolysate slurry using a two-step washing strategy with 99.3% of sugars recovery. Cutaneotrichosporon oleaginosum showed excellent capacity for assimilating both monosaccharides and oligosaccharides for lipid production using the fed-batch culture mode. Lipid concentration, content, and yield gained 42.3 g/L, 64.6%, and 20.4 g/100 g, respectively. Turbid hydrolysate collected with high recovery of high-concentration sugars and simplified process could be directly served as feeding medium. In general, the overall hydrolysis yield and lipid yield using fed-batch mode accounted for 93.2% and 97.6% of those using batch mode, respectively, resulting in a lipid output of 102.8 g/kg raw corn stover. The fatty acid composition and the prediction of biodiesel properties of lipid samples indicated the suitability for high-quality fuel production. This study provided valuable information for designing highly efficient lignocelluloses-to-biodiesel routes. [ABSTRACT FROM AUTHOR]

Background: The model yeast, Saccharomyces cerevisiae, is not known to be oleaginous. However, an industrial wild-type strain, D5A, was shown to accumulate over 20% storage lipids from glucose when growth is nitrogen-limited compared to no more than 7% lipid accumulation without nitrogen stress. Methods and results: To elucidate the mechanisms of S. cerevisiae D5A oleaginicity, we compared physiological and metabolic changes; as well as the transcriptional profiles of the oleaginous industrial strain, D5A, and a non-oleaginous laboratory strain, BY4741, under normal and nitrogen-limited conditions using analytic techniques and next-generation sequencing-based RNA-Seq transcriptomics. Transcriptional levels for genes associated with fatty acid biosynthesis, nitrogen metabolism, amino acid catabolism, as well as the pentose phosphate pathway and ethanol oxidation in central carbon (C) metabolism, were up-regulated in D5A during nitrogen deprivation. Despite increased carbon flux to lipids, most gene-encoding enzymes involved in triacylglycerol (TAG) assembly were expressed at similar levels regardless of the varying nitrogen concentrations in the growth media and strain backgrounds. Phospholipid turnover also contributed to TAG accumulation through increased precursor production with the down-regulation of subsequent phospholipid synthesis steps. Our results also demonstrated that nitrogen assimilation via the glutamate–glutamine pathway and amino acid metabolism, as well as the fluxes of carbon and reductants from central C metabolism, are integral to the general oleaginicity of D5A, which resulted in the enhanced lipid storage during nitrogen deprivation. Conclusion: This work demonstrated the disequilibrium and rebalance of carbon and nitrogen contribution to the accumulation of lipids in the oleaginous yeast S. cerevisiae D5A. Rather than TAG assembly from acyl groups, the major switches for the enhanced lipid accumulation of D5A (i.e., fatty acid biosynthesis) are the increases of cytosolic pools of acetyl-CoA and NADPH, as well as alternative nitrogen assimilation. [ABSTRACT FROM AUTHOR]

Background: Compared with other general energy crops, microalgae are more compatible with desert conditions. In addition, microalgae cultivated in desert regions can be used to develop biodiesel. Therefore, screening oil-rich microalgae, and researching the algae growth, CO2 fixation and oil yield in desert areas not only effectively utilize the idle desertification lands and other resources, but also reduce CO2 emission. Results: Monoraphidium dybowskii LB50 can be efficiently cultured in the desert area using light resources, and lipid yield can be effectively improved using two-stage induction and semi-continuous culture modes in open raceway ponds (ORPs). Lipid content (LC) and lipid productivity (LP) were increased by 20% under two-stage industrial salt induction, whereas biomass productivity (BP) increased by 80% to enhance LP under semi-continuous mode in 5 m2 ORPs. After 3 years of operation, M. dybowskii LB50 was successfully and stably cultivated under semi-continuous mode for a month during five cycles of repeated culture in a 200 m2 ORP in the desert area. This culture mode reduced the supply of the original species. The BP and CO2 fixation rate were maintained at 18 and 33 g m−2 day−1, respectively. Moreover, LC decreased only during the fifth cycle of repeated culture. Evaporation occurred at 0.9–1.8 L m−2 day−1, which corresponded to 6.5–13% of evaporation loss rate. Semi-continuous and two-stage salt induction culture modes can reduce energy consumption and increase energy balance through the energy consumption analysis of life cycle. Conclusion: This study demonstrates the feasibility of combining biodiesel production and CO2 fixation using microalgae grown as feedstock under culture modes with ORPs by using the resources in the desert area. The understanding of evaporation loss and the sustainability of semi-continuous culture render this approach practically viable. The novel strategy may be a promising alternative to existing technology for CO2 emission reduction and biofuel production. [ABSTRACT FROM AUTHOR]

With the continuing consumption of resources and increasingly prominent environmental issues, microalgal resource utilization has received extensive attention. In this study, based on the microalgal investigation in desert biological soil crusts (BSCs) using pyrosequencing technology, the cultivated crust microalgae were further isolated in order to obtain high quality microalgae for resource utilization. The results showed that with crust development and succession, microalgal diversity gradually decreased, including the number of operational taxonomic units (OTUs) and genus, although Microcoleus always was the dominant genera. Pyrosequencing obtained 630 OTUs of cyanobacteria, 25 OTUs of green algae and 9 OTUs of diatom; however, part of cultivated microalgae still could not yet be detected due to the DNA extraction preferences and errors caused by PCR amplification. After isolation, four strains were purified and cultivated, including two filamentous cyanobacteria Microcoleus vaginatus BSC-06 and Scytonema javanicum BSC-39, and two unicellular green algae Chlorella sp. BSC-24 and Monoraphidium dybowskii BSC-81. The two green algae grew fast (>250 mg L -1  d -1 ), and achieved high lipid productivity up to 75–85 mg L -1  d -1 , with lipid content of 28.7–39.0%, thus was considered as promising feedstock for biodiesel production. In addition, the two crust cyanobacteria could be used to construct artificial cyanobacterial soil crusts in desertification control, although their biomass accumulation was not as high as that in the green algae. Ultimately, combining biodiesel production with desertification control would not only improve desert environments, but also provide ideal places for the local microalgal resource exploitation, further promoting desert socioeconomic development. [ABSTRACT FROM AUTHOR]

The European land carbon uptake has been heavily impacted by several recent severe droughts, yet quantitative estimates of carbon uptake anomalies are uncertain. Atmospheric CO2 inverse models (AIMs) provide observation‐based estimates of the large‐scale carbon flux dynamics, but how well they capture drought impacts on the terrestrial carbon uptake is poorly known. Here we assessed the capacity of state‐of‐the‐art AIMs in monitoring drought impacts on the European carbon uptake over 2001–2015 using observations of environmental variability and vegetation function and made comparisons with bottom‐up estimates of carbon uptake anomalies. We found that global inversions with only limited surface CO2 observations give divergent estimates of drought impacts. Regional inversions assimilating denser CO2 observations over Europe demonstrated some improved consistency, with all inversions capturing a reduction in carbon uptake during the 2012 drought. However, they failed to capture the reduction caused by the 2015 drought. Finally, we found that a set of inversions that assimilated satellite XCO2 or assimilated environmental variables plus surface CO2 observations better captured carbon uptake anomalies induced by both the 2012 and 2015 droughts. In addition, the recent Orbiting Carbon Observatory—2 XCO2 inversions showed good potential in capturing drought impacts, with better performances for larger‐scale droughts like the 2018 drought. These results suggest that surface CO2 observations may still be too sparse to fully capture the impact of drought on the carbon cycle at subcontinental scales over Europe, and satellite XCO2 and ancillary environmental data can be used to improve observational constraints in atmospheric inversion systems. Plain Language Summary: Atmospheric CO2 inverse models (AIMs) are useful tools for quantifying the response of large‐scale carbon uptake to climate extremes, but their capacity for monitoring drought impacts, particularly at regional scales, is not fully explored. In this study, we assessed the capacity of state‐of‐the‐art AIMs for monitoring drought impacts on the European land carbon uptake over 2001–2015 using a large array of observational and model data sets. We found: (a) global inversions with only limited surface CO2 observations face a great challenge in monitoring drought impacts on the European carbon uptake; (b) Regional inversions assimilated denser CO2 observations over Europe, for the EUROCOM project, demonstrated some improved consistency but are still deficient, showing divergent estimates in interannual variability of carbon uptake for most years; and (c) A set of inversion systems that assimilated satellite XCO2 or assimilated environmental variables plus surface CO2 observations better captured annual and seasonal anomalies caused by droughts. Our study demonstrates that surface CO2 observations may still be too sparse to fully capture the impact of drought on the carbon cycle at subcontinental scales over Europe, whereby satellite XCO2 and ancillary environmental data can offer observational constraints for improving the estimates. Key Points: Global inversions with only limited surface CO2 observations give divergent estimates of drought impacts on the European carbon uptakeRegional inversions assimilating denser CO2 observations over Europe demonstrate some improved consistency but are still deficientThe inversions assimilating satellite XCO2 or environmental variables in addition to surface CO2 largely improve the estimates [ABSTRACT FROM AUTHOR]

Many microalgae are reported to accumulate TAG under high concentrations of bicarbonate and nitrogen deficiency, but their physiological responses remain unknown and the associated applied technology is rarely explored. We found that single high concentration of bicarbonate did not enhance lipid content, except when combined with nitrogen limitation in Desmodesmus sp. NMX451, and the lipid contents obtained were independent from nitrogen limitation and alkalinity stress. Further analysis showed that adding bicarbonate not only retarded the cell cycle, repressed starch accumulation but also promoted polar lipid content. Nitrogen limitation meantime caused protein and chlorophyll degradation with a corresponding increase in total lipid content. Following the aforementioned insights, combined cultivation was performed at an outdoor 5 L scale, and higher biomass and lipid productivities were obtained. These results suggest that bicarbonate can be used as a 'trigger' for rapid lipid accumulation in microalgae during nitrogen depletion, and this is an effective new strategy for the cultivation of oleaginous microalgae. [ABSTRACT FROM AUTHOR]

The aim of this study was to identify the most promising species as biodiesel feedstock for large-scale cultivation in north China. Eight species of microalgae, selected on the basis of indoor screening, were tested for lipid productivity and the suitability of their fatty acid profiles for biodiesel production under outdoor conditions. Among them, three species Desmodesmus sp. NMX451, Desmodesmus sp. T28-1 and Scenedesmus obtusus XJ-15 were selected for further characterization due to their possessing higher lipid productivities and favorable biodiesel properties. The best strain was S. obtusus XJ-15, with highest biomass productivity of 20.2 g m −2 d −1 and highest lipid content of 31.7% in a culture of 140 L. S. obtusus XJ-15 was further identified as the best candidate for liquid biofuel production, characterized by average areal growth rate of 23.8 g m −2 d −1 and stable lipid content of above 31.0% under a scale of 1400 L over a season. [ABSTRACT FROM AUTHOR]

Zymomonas mobilis is a native ethanologen with the unique anaerobic Entner Doudoroff pathway. In this study, a heterologous poly-3-hydroxybutyrate (PHB) pathway was engineered into Z. mobilis. Genetic strategies were applied to improve PHB production including overexpression of the phaCAB operon by using a strong promoter and/or increasing its copy numbers, cofactor balance by overexpressing the endogenous genes for NADPH balance, and competition of acetaldehyde for acetyl-CoA generation through the ethanol utilization pathway (EUP). PHB contents in recombinant strains were enhanced gradually. The highest PHB content of 37.68 ± 2.56% (dry cell weight, DCW) was achieved in the ZMPtN2-EUP strain, which contains copies of the phaCAB operon in both the chromosome and plasmid, an extra copy of the native zwf gene for cofactor balance, and genes for the EUP. The PHB production in ZMPtN2-EUP was further improved by optimizing the C/N ratio, and the PHB content was increased to 50.30 ± 3.39% (DCW) at a C/N ratio of 20/2 (20 g L−1 glucose and 2 g L−1 yeast extract). ZMPtN2-EUP was then empowered with the self-flocculating phenotype using a native CRISPR-Cas genome editing system to generate ZMPt-FloN2-EUP for biomass recovery through gravity sedimentation. The PHB content of 40.57 ± 0.60% (DCW) in ZMPt-FloN2-EUP with self-flocculation capability was slightly higher than that of ZMPtN2-EUP, which further increased to 74.03 ± 1.81% (DCW) at a C/N ratio of 20/2. Moreover, ZMPtN2-EUP was able to be used as a microbial biocatalyst for continuous co-production of high-titer ethanol and PHB without affecting ethanol percentage productivity. Our study thus demonstrated that the strategy to combine genetic and process engineering is effective to develop non-model microorganisms for heterologous production of bio-based chemicals, and the capability of Z. mobilis for continuous co-production of high-titer ethanol and PHB exhibited that Z. mobilis is a promising chassis for economic biochemical production. [ABSTRACT FROM AUTHOR]

Background: Efficient use of glucose and xylose is a key for the economic production of lignocellulosic biofuels and biochemicals, and different recombinant strains have been constructed for xylose utilization including those using Zymomonas mobilis as the host. However, the xylose utilization efficiency still needs to be improved. In this work, the strategy of combining metabolic engineering and adaptive laboratory evolution (ALE) was employed to develop recombinant Z. mobilis strains that can utilize xylose efficiently at high concentrations, and NGS-based genome resequencing and RNA-Seq transcriptomics were performed for strains evolved after serial transfers in different media to understand the impact of xylose and differences among strains with different xylose-utilization capabilities at molecular level. Results: Heterologous genes encoding xylose isomerase and xylulokinase were evaluated, which were then introduced into xylose-utilizing strain Z. mobilis 8b to enhance its capacity of xylose utilization. The results demonstrated that the effect of three xylose isomerases on xylose utilization was different, and the increase of copy number of xylose metabolism genes can improve xylose utilization. Among various recombinant strains constructed, the xylose utilization capacity of the recombinant strain 8b-RsXI-xylB was the best, which was further improved through continuous adaption with 38 transfers over 100 days in 50 g/L xylose media. The fermentation performances of the parental strain 8b, the evolved 8b-S38 strain with the best xylose utilization capability, and the intermediate strain 8b-S8 in different media were compared, and the results showed that only 8b-S38 could completely consume xylose at 50 g/L and 100 g/L concentrations. In addition, the xylose consumption rate of 8b-S38 was faster than that of 8b at different xylose concentrations from 50 to 150 g/L, and the ethanol yield increased by 16 ~ 40%, respectively. The results of the mixed-sugar fermentation also demonstrated that 8b-S38 had a higher xylose consumption rate than 8b, and its maximum ethanol productivity was 1.2 ~ 1.4 times higher than that of 8b and 8b-S8. Whole-genome resequencing identified three common genetic changes in 8b-S38 compared with 8b and 8b-S8. RNA-Seq study demonstrated that the expression levels of genes encoding chaperone proteins, ATP-dependent proteases, phage shock proteins, ribosomal proteins, flagellar operons, and transcriptional regulators were significantly increased in xylose media in 8b-S38. The up-regulated expression of these genes may therefore contribute to the efficient xylose utilization of 8b-S38 by maintaining the normal cell metabolism and growth, repairing cellular damages, and rebalancing cellular energy to help cells resist the stressful environment. Conclusions: This study provides gene candidates to improve xylose utilization, and the result of expressing an extra copy of xylose isomerase and xylulokinase improved xylose utilization also provides a direction for efficient xylose-utilization strain development in other microorganisms. In addition, this study demonstrated the necessity to combine metabolic engineering and ALE for industrial strain development. The recombinant strain 8b-S38 can efficiently metabolize xylose for ethanol fermentation at high xylose concentrations as well as in mixed sugars of glucose and xylose, which could be further developed as the microbial biocatalyst for the production of lignocellulosic biofuels and biochemicals. [ABSTRACT FROM AUTHOR]

Background: Biofuels and value-added biochemicals derived from renewable biomass via biochemical conversion have attracted considerable attention to meet global sustainable energy and environmental goals. Isobutanol is a four-carbon alcohol with many advantages that make it attractive as a fossil-fuel alternative. Zymomonas mobilis is a highly efficient, anaerobic, ethanologenic bacterium making it a promising industrial platform for use in a biorefinery. Results: In this study, the effect of isobutanol on Z. mobilis was investigated, and various isobutanol-producing recombinant strains were constructed. The results showed that the Z. mobilis parental strain was able to grow in the presence of isobutanol below 12 g/L while concentrations greater than 16 g/L inhibited cell growth. Integration of the heterologous gene encoding 2-ketoisovalerate decarboxylase such as kdcA from Lactococcus lactis is required for isobutanol production in Z. mobilis. Moreover, isobutanol production increased from nearly zero to 100–150 mg/L in recombinant strains containing the kdcA gene driven by the tetracycline-inducible promoter Ptet. In addition, we determined that overexpression of a heterologous als gene and two native genes (ilvC and ilvD) involved in valine metabolism in a recombinant Z. mobilis strain expressing kdcA can divert pyruvate from ethanol production to isobutanol biosynthesis. This engineering improved isobutanol production to above 1 g/L. Finally, recombinant strains containing both a synthetic operon, als-ilvC-ilvD, driven by Ptet and the kdcA gene driven by the constitutive strong promoter, Pgap, were determined to greatly enhance isobutanol production with a maximum titer about 4.0 g/L. Finally, isobutanol production was negatively affected by aeration with more isobutanol being produced in more poorly aerated flasks. Conclusions: This study demonstrated that overexpression of kdcA in combination with a synthetic heterologous operon, als-ilvC-ilvD, is crucial for diverting pyruvate from ethanol production for enhanced isobutanol biosynthesis. Moreover, this study also provides a strategy for harnessing the valine metabolic pathway for future production of other pyruvate-derived biochemicals in Z. mobilis. [ABSTRACT FROM AUTHOR]

The paddy rice fields act as an important anthropogenic source of methane (CH 4) to the atmosphere. The study of pattern, magnitude, and environmental controls of CH 4 emissions are still insufficient due to limited measurements and understand of underlying drivers for variations of CH 4 fluxes at different temporal scales. In this study, CH 4 fluxes from a rice-wheat rotation agroecosystem in eastern China were continuously measured using the eddy covariance technique. The diurnal and seasonal variations of CH 4 flux and potential controlling factors in 2016 were analyzed using wavelet coherence, conditional Granger causality, correlation analysis and path analysis methods. CH 4 fluxes showed distinguishable diurnal variations with single peaks during 13: 00–16: 00 local time. At the diurnal timescale, gross primary productivity (GPP) regulates CH 4 fluxes after accounting for the effects of latent heat flux (LE), air temperature (TA), and soil temperature (TS) on CH 4 fluxes. LE mirrored the diurnal pattern of CH 4 fluxes when the effects of TA and TS on CH 4 fluxes were considered. Daily CH 4 fluxes exhibited large seasonal variations, with the largest daily CH 4 flux of 1191.78 mg C-CH 4 m−2 d−1 on 29 July 2016. The daily CH 4 fluxes were continuously low in the growing season of wheat, and sharply increased from very low values in late June to peaks in late July and early August, and then gradually decreased to low values at the end of the rice growing season in late November and early December. Correlation analysis and path analysis showed that seasonal variations of soil temperature, air temperature, and GPP had strong effects on daily CH 4 fluxes during pre-panicle initiation of the rice growing season, while soil temperature and leaf area index (LAI) had very strong effects on daily CH 4 fluxes during the post-panicle initiation stage. The total of CH 4 fluxes from the rice-wheat rotation agroecosystem into the atmosphere amounted to 58.08 ± 9.87 g C m−2 in 2016, and the annual net carbon (C) budget and greenhouse gas (GHG) budget were 163.50 ± 9.87 g C m−2 and 2322.53 ± 329.00 g CO 2 eq m−2, respectively. This study represents a comprehensive assessment of fluxes and drivers of CH 4 from a rice-wheat rotation agroecosystem at different timescales. Additionally, the consecutive data of CH 4 emission in this region will also useful for model calibration and validation. Unlabelled Image • CH 4 fluxes from a rice-wheat rotation agroecosystem peaked in early afternoon. • Seasonal variations of daily CH 4 fluxes can be explain by daily TA, TS, GPP, and LAI. • The rice-wheat rotation agroecosystem in eastern China acted as C and GHG sources in 2016. [ABSTRACT FROM AUTHOR]

Light precipitation events generally occur much more frequently than events of other precipitation intensities. Changes in light precipitation amounts and days (length) over time have profound implications for climate change. There is a lack of quantitative monitoring indicators or in-depth analysis techniques for atmospheric circulation mechanisms of regional light precipitation events, especially in climate transitional zones. The Huai River Eco-economic Corridor (HREC) served as a case area in this study as we assessed trends in light precipitation events and their possible atmospheric circulation mechanisms. A significant decreasing trend in the light precipitation events is observed and appears to be mainly concentrated in the lower intensities (0.1 ≤ P<2 mm/day). The decreasing trend is more obvious for consecutive than discrete light precipitation events. The mutation points for annual consecutive light precipitation events were found in 1977/1978, and averages in the later years of the observation period (1978–2014) fell significantly below those of the earlier period (1961–1977). Atmospheric circulation variables corresponding to the light precipitation days with intensity of 0.1–2 mm/day revealed that the decreasing trends in water vapor transport budgets, low cloud cover, and total column cloud liquid water may be the primary causes of decreased light precipitation events. The decreasing trends in light precipitation events were also likely attributable to increases in water vapor flux divergence, air temperature, and vertical velocity values. • Decrease in light precipitation events is mainly concentrated at lower light precipitation intensities (0.1 ≤ P<2 mm/day). • Consecutive light precipitation events decrease to greater extent than discrete light precipitation events. • Decreases in light precipitation events are affected by atmospheric circulation patterns in HREC. [ABSTRACT FROM AUTHOR]

Highlights: [•] 0.25gL−1 urea is the optima for biomass accumulation in D. abundans. [•] NaCl was outstanding of different salts (NaCl, NaHCO3, NaAc and NaS2O3) on lipid induction. [•] Higher lipid productivity was obtained during the optimized cultivation process. [•] 1.79gL−1 of biomass concentration was the time point for NaCl addition. [•] Strategy of NaCl addition for cultivating D. abundans was cost-efficient and net energy-positive. [Copyright &y& Elsevier]

A novel Fe/La oxide magnetic microspheres for enhanced As(V) removal from diluted wastewater was synthesized and characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectrometer, and vibrating sample magnetometer. The prepared Fe/La oxide magnetic microspheres possessed satisfactory pore size distribution with stable spheres structure. Adsorption of arsenate onto Fe/La OMMs was first investigated using batch experiments for the determination of pH edge, adsorption kinetics, and isotherm. The removal of As(V) by Fe/La oxide magnetic microspheres could reach almost 100% under As(V) solution of 1 mg/L at the optimum adsorbent dosage of 0.1 g/L. The adsorption kinetics followed an intraparticle diffusion model, and the adsorption isotherm was well described by the Langmuir model with the maximum adsorption capacity of 62.32 mg/g for As(V) at pH 4. Besides, the Fe/La oxide magnetic microspheres performed well in selectivity and magnetic separation. PHREEQC programming suggested the adsorption process could be better described by the surface complexation model and reinforced the understanding of the Fe/La oxide magnetic microspheres in true wastewater treatment applications. The adsorption mechanism is attributed to surface complexation and intraparticle diffusion, including electrostatic interaction, ligand exchange, and complex formation. The developed Fe/La oxide magnetic microspheres showed great potential in the advanced As(V) processing for the dilute natural arsenic-contaminated water. Image 1 • A novel porous Fe–La oxide magnetic microspheres was synthesized. • Efficient removal of As(V) was achieved at diluted concentrations. • PHREEQC geochemical modelling was used to describe the adsorption behaviour. • Outer- and inner-sphere complexation were main mechanisms for excellent As(V) removal. [ABSTRACT FROM AUTHOR]

Spatially continuous soil thickness data at large scales are usually not readily available and are often difficult and expensive to acquire. Various machine learning algorithms have become very popular in digital soil mapping to predict and map the spatial distribution of soil properties. Identifying the controlling environmental variables of soil thickness and selecting suitable machine learning algorithms are vitally important in modeling. In this study, 11 quantitative and four qualitative environmental variables were selected to explore the main variables that affect soil thickness. Four commonly used machine learning algorithms (multiple linear regression (MLR), support vector regression (SVR), random forest (RF), and extreme gradient boosting (XGBoost) were evaluated as individual models to separately predict and obtain a soil thickness distribution map in Henan Province, China. In addition, the two stacking ensemble models using least absolute shrinkage and selection operator (LASSO) and generalized boosted regression model (GBM) were tested and applied to build the most reliable and accurate estimation model. The results showed that variable selection was a very important part of soil thickness modeling. Topographic wetness index (TWI), slope, elevation, land use and enhanced vegetation index (EVI) were the most influential environmental variables in soil thickness modeling. Comparative results showed that the XGBoost model outperformed the MLR, RF and SVR models. Importantly, the two stacking models achieved higher performance than the single model, especially when using GBM. In terms of accuracy, the proposed stacking method explained 64.0% of the variation for soil thickness. The results of our study provide useful alternative approaches for mapping soil thickness, with potential for use with other soil properties. [ABSTRACT FROM AUTHOR]

AFM images of EPS-K (a) and EPS-B (b) and 3D-EEM images of of EPS-K (c) and EPS-B (d) • EPS-K and EPS-B were extracted from pure strains in activated sludge. • Both EPS showed superb performances for Hg(II) immobilization. • FTIR, 3D-EEM, XPS, EDS, PT were used to characterize the adsorption. • EPS-K and EPS-B showed different characteristics and sorption mechanisms. • S and P play important roles in the Hg(II) complexation. Extracellular polymeric substances (EPS), with abundant functional groups, play important roles in heavy metal elimination in sludge systems. In this paper, EPS-K and EPS-B were extracted from Klebsiella sp. NT8 and Bacillus sp. NT10 in activated sludge, and evaluated for their potential in Hg(II) sorption. AFM observation showed EPS possessed huge surface area. The adsorption tests indicated EPS-K and EPS-B were both superb adsorbents with the maximum sorption capacity of 2597.62 and 2617.23 mg/g, respectively and the adsorption followed the pseudo-second-order kinetics and Langmuir isotherm model. FT-IR and 3D-EEM analysis showed aromatic and tryptophan-like proteins in EPS-B, while tryptophan-like protein and humic substance in EPS-K contributed to Hg(II) binding, with higher site binding number in EPS-B. EDS and XPS further highlighted the S- and P-based functional groups in the complexation with Hg besides N. This work provides new insights into microbial products from sludge with biosorbent potential for metal treatment. [ABSTRACT FROM AUTHOR]