Institute of Hydrobiology, Chinese Academy Of Sciences
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Mechanistic study on laccase-mediated formation of Fe-OM associations in peatlands
No full textPeatlands represent one of the largest terrestrial carbon pools. Phenol oxidase is widely considered to play a critical role in the decomposition of organic matter in peatlands, which is known as the "enzymatic latch". However, our recent studies have indicated that the formation of iron-organic matter (Fe-OM) associations is more likely to occur in the presence of laccase, the largest class of phenol oxidases in soils. As the formation of Fe-OM associations is recognized as an important stabilization mechanism for soil organic matter, further clarification of the potential mechanisms contributes to a better understanding of the role of laccase in peatland carbon sequestration. In this study, a series of experiments using different phenolic compounds and peat-derived dissolved organic matter (DOM) were performed. The results from liquid chromatography-high-resolution mass spectrometry (LC-HRMS) and gel permeation chromatography (GPC) analyses indicated that laccase catalyzed the polymerization of phenolics and peat-derived DOM by coupling of the C-O bond, the C-C bond and the C-C/C-O bonds. The polymerized products can combine more effectively with Fe to form Fe-OM associations. FTIR spectral analysis indicated that organic matter associated with Fe under laccase catalysis contained more oxygen-containing functional groups but fewer aromatic C]C bonds. Although laccase catalysis can change the chemical structure of organic matter, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed minimal influence of laccase on the Fe chemical species in the Fe-OM associations. Thus, we propose that laccase mediated the formation of Fe-OM associations by polymerizing organic matter and by increasing the O/C ratio of organic matter. In addition, laccase can improve the sequestration of organic carbon by increasing the C/Fe molar ratio of the formed Fe-OM associations. This mechanism may provide further insight into the role of laccase in the carbon cycling in peatlands
Metagenomic evidence reveals denitrifying community diversity rather than abundance drives nitrate removal in stormwater biofilters amended with different organic and inorganic electron donors
No full textVarious sole and mixed electron donors were tested to promote the denitrification rate and nitrate removal efficiency in biofilter systems with high phosphate and ammonia removal efficiency (92.6% and 95.3% respectively). Compared to sole electron donors, complex organic carbon (bits of wood and straw) substantially improved the denitrification rate and nitrate removal efficiency (from 6.3%-18.5% to35.4%) by shifting the denitrifying microbial community composition, even though the relative abundance of functional genes mediating denitrification decreased. The mixed electron donor combining complex organic carbon with sulfur, iron and CH4 further promoted nitrate removal efficiency by 37.2%. The significantly higher abundance and diversity of bacteria mediating organic carbon decomposition in the treatments with complex organic carbon indicated the continuous production of organic carbon with small molecular weights, which provided sustainable and effective electron donor for denitrification. However, sole sulfur or iron did not effectively promote the denitrification rate and nitrogen removal efficiency, even though the related microbial community had been formed. (C) 2020 Elsevier Ltd. All rights reserved
Ultrafiltration and microfiltration membrane performance, cleaning, and flux recovery for microalgal harvesting
No full textMembrane material, pore size, and cleaning strategy are important factors for microalgal membrane harvesting. In this study, harvesting ofScenedesmus acuminatuscultivated in pilot scale using nine ultrafiltration and three microfiltration membranes was carried out in cross-flow filtration system to compare their filtration performance and flux recovery after physical and chemical cleaning. The 0.45-mu m PVDF-AsahiKASEI membrane had the highest average flux of 513.6 L m(-2) h(-1)among 12 membranes and 50-kDa PVC-Litree membrane had the highest average flux of 98.0 L m(-2) h(-1)among nine ultrafiltration membranes for 60 LS. acuminatussuspension harvesting. There were significantly positive correlations between membrane pore size, pure water flux, and average flux forS. acuminatussuspension harvesting. Generally, ultrafiltration membrane had moderate total fouling index (TFI) and high proportion of hydraulic reversible fouling index (HRFI) of more than 95%. The 0.45-mu m PVDF-AsahiKASEI membrane had a low TFI but the lowest proportion of HRFI, associated with the residual microalgal cells, debris, and colloids on the inner surface and top ends of some cells inserted to big membrane pores, demonstrated by SEM image and reduced porosity from 65.9 to 60.2%. Compared to soaking cleaning, circulation cleaning strategy had a better flux recovery efficiency for 0.45-mu m PVDF-AsahiKASEI membrane, proving that it would be a potential way in membrane chemical cleaning. This study demonstrated that microfiltration with high flux has great potential in microalgal harvesting if flux recovery efficiency can be significantly increased using suitable cleaning strategy such as circulation cleaning strategy
Genetic structure and demographic histories of two sympatric Culter species in eastern China
No full textGeographic isolation is a key factor in shaping the genetic structure of many fish species.Two sympatric species,Culter alburnus and C.mongolicus,are economically important fish that are widely distributed in China and have been recently used as new aquaculture species.We used the mitochondrial DNA control region(CR)as a marker to investigate the genetic structure of the two species.Phylogenetic analysis revealed two major lineages(Lineages I and II)that were highly consistent with geographical patterns for C.alburnus and C.mongolicus.Based on genetic distance,the Zhujiang(Pearl)River Basin(ZRB)populations potentially represented a cryptic subspecies,which might be differentiated as the result of strict geographic isolation,an earlier diverged event,or peripheral areas.Genetic diversity analysis suggested that the Changjiang(Yangtze)River Basin(CRB)populations are located at,or near the core region of their origination,not only due to the larger population size at the CRB,but also their habitat diversity and suitability for its survival,and the genetic diversity dif ferences among basin populations were significant for the two species.Moreover,demographic analysis indicated that the two Culter species and most populations had undergone a period of population expansion during warm interglacial periods.However,the C.alburnus population of Huaihe River Basin(Weishan Lake)exhibited different patterns during the interglacial period,which may due to the latest diverged time of HRB and Weishan Lake located at the permafrost.Notably,the ZRB(in Songtao Reservoir)C.mongolicus population showed no genetic diversity and had a unique haplotype,which could be treated as a special gene pool for species conservation.In summary,geographic isolation is most likely responsible for the two Culter species distribution patterns
Better assessments of greenhouse gas emissions from global fish ponds needed to adequately evaluate aquaculture footprint
No full textWhile providing protein for a fast-growing human population, the ongoing boom in global aquaculture comes with environmental costs. Particularly, the intense greenhouse gas (GHG) emissions reported for several aquaculture systems are a source of concern. Still, we argue that actual emissions could be multiple times higher than currently thought. Most studies supporting existing estimates solely rely on measurements of water-atmosphere diffusive fluxes of GHG, whereas methane (CH4) and nitrous oxide (N2O) emissions during drainage and refilling and CH4 bubbles emerging from sediments are largely ignored. Yet, abundant evidence for similar aquatic ecosystems suggests that these largely unaccounted emission pathways may be responsible for a large share of annual GHG emissions. Uncertainties from overlooking important emission pathways may have serious consequences, including incorrect advice on mitigation strategies and overly optimistic assessments of the GHG footprint of cultured freshwater fish. To ensure a low-carbon future for global aquaculture, we contend that GHG assessments in fish-farming ponds must extend beyond the focus on diffusive water-atmosphere fluxes and include all emission pathways and possible carbon burial in the sediment. In parallel, we call for a better understanding of the biological, microbiological and physical drivers of aquaculture emissions to effectively support mitigation strategies to minimize the footprint of this nutritionally valuable protein source. (C) 2020 Elsevier B.V. All rights reserved
Investigation of an Antioxidative System for Salinity Tolerance in Oenanthe javanica
No full textAbiotic stress, such as drought and salinity, severely affect the growth and yield of many plants. Oenanthe javanica (commonly known as water dropwort) is an important vegetable that is grown in the saline-alkali soils of East Asia, where salinity is the limiting environmental factor. To study the defense mechanism of salt stress responses in water dropwort, we studied two water dropwort cultivars, V11E0022 and V11E0135, based on phenotypic and physiological indexes. We found that V11E0022 were tolerant to salt stress, as a result of good antioxidant defense system in the form of osmolyte (proline), antioxidants (polyphenols and flavonoids), and antioxidant enzymes (APX and CAT), which provided novel insights for salt-tolerant mechanisms. Then, a comparative transcriptomic analysis was conducted, and Gene Ontology (GO) analysis revealed that differentially expressed genes (DEGs) involved in the carbohydrate metabolic process could reduce oxidative stress and enhance energy production that can help in adaptation against salt stress. Similarly, lipid metabolic processes can also enhance tolerance against salt stress by reducing the transpiration rate, H2O2, and oxidative stress. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that DEGs involved in hormone signals transduction pathway promoted the activities of antioxidant enzymes and reduced oxidative stress; likewise, arginine and proline metabolism, and flavonoid pathways also stimulated the biosynthesis of proline and flavonoids, respectively, in response to salt stress. Moreover, transcription factors (TFs) were also identified, which play an important role in salt stress tolerance of water dropwort. The finding of this study will be helpful for crop improvement under salt stress
Effects of a Type I RM System on Gene Expression and Glycogen Catabolism inSynechocystissp. PCC 6803
No full textIncreasing evidence has shown that DNA methylation is involved in gene regulation in prokaryotes. However, there have been very limited reports about the role of DNA methylation in regulation of gene expression and physiological functions in cyanobacteria. InSynechocystissp. PCC 6803, four genes on the plasmid pSYSX are predicted to encode the type I restriction-methylation system,slr6095andslr6096for the M subunit,slr6097for the S subunit andslr6102for theRsubunit. Compared to the wild type,slr6095,slr6096, andslr6097mutants lacked the GG(m6)AN(7)TTGG/CCA(m6)AN(7)TCC methylation in genomic DNA. Transcriptomic analysis indicated that 171 genes were reproducibly up- or down-regulated in all three mutants relative to the wild type. The changed expression of some genes, includingsll1356for glycogen phosphorylase (GlgP), was associated with the loss of GG(m6)AN(7)TTGG/CCA(m6)AN(7)TCC methylation in the coding regions or the upstream non-coding sequences. Inactivation ofslr6095,slr6096, orslr6097increased the expression ofsll1356and the GlgP activity but lowered the glycogen content. These results indicated that the DNA methylation by a type I RM system could alter the expression of certain genes and physiological functions inSynechocystissp. PCC 6803
Influence of metals and metalloids on the composition and fluorescence quenching of the extracellular polymeric substances produced by the polymorphic fungusAureobasidium pullulans
No full textAureobasidium pullulansis a ubiquitous and widely distributed fungus in the environment, and exhibits substantial tolerance against toxic metals. However, the interactions between metals and metalloids with the copious extracellular polymeric substances (EPS) produced byA. pullulansand possible relationships to tolerance are not well understood. In this study, it was found that mercury (Hg) and selenium (Se), as selenite, not only significantly inhibited growth ofA. pullulansbut also affected the composition of produced EPS. Lead (Pb) showed little influence on EPS yield or composition. The interactions of EPS fromA. pullulanswith the tested metals and metalloids depended on the specific element and their concentration. Fluorescence intensity measurements of the EPS showed that the presence of metal(loid)s stimulated the production of extracellular tryptophan-like and aromatic protein-like substances. Examination of fluorescence quenching and calculation of binding constants revealed that the fluorescence quenching process for Hg; arsenic (As), as arsenite; and Pb to EPS were mainly governed by static quenching which resulted in the formation of a stable non-fluorescent complexes between the EPS and metal(loid)s. Se showed no significant interaction with the EPS according to fluorescence quenching. These results provide further understanding of the interactions between metals and metalloids and EPS produced by fungi and their contribution to metal(loid) tolerance
Properties of CaO2 for H2O2 release and phosphate removal and its feasibility in controlling Microcystis blooms
No full textCalcium peroxide (CP) has been widely applied in environmental remediation, but few studies have reported its application in controllingMicrocystisblooms. To recognize its feasibility for mitigatingMicrocystisblooms, the properties of CP in terms of hydrogen peroxide (HP) release and phosphate removal were investigated at different CP doses, temperatures, and initial pH values. HP release kinetics followed the Higuchi model. Batch experiments conducted in this study suggested that the HP yield and release rate were positively correlated with the CP dose. Increasing temperature decreased the HP yield but accelerated the HP release rate. The phosphate removal kinetics were well simulated by the pseudo-second-order model. The batch experiments suggested that an increased CP dose enhanced the phosphate removal capacity, but it did not affect the phosphate removal rate. Moreover, increased temperature accelerated both phosphate removal capacity and rate. However, the initial pH of low-buffer-capacity solutions did not notably affect HP release and phosphate removal. According to laboratory experiments, HP released from CP could impair photosynthetic activity, resulting inMicrocystismortality. Furthermore, the reduced phosphate concentration in the solutions suggested that CP could facilitate the control of eutrophication, which directly reduced bloom formation. Hence, our results confirmed CP as a promising algicide forMicrocystisbloom control, and it is worthwhile to develop novel methods for bloom mitigation based on CP
Combined effects of fish cage culture and increased fishing pressure on wild fish assemblages in a large reservoir, Yangtze River basin, China
No full textLocal fishers often claim that cage culture practices in reservoirs result in high fish catches as fish cages attract a diverse variety of wild fish, which mainly aggregate to forage on waste from the practices. Previous studies have focused on fish aggregation effects brought about by fish cages. In the present study, we explored the responses of wild fish assemblages to fish cages and increased fishing pressure in the vicinity of cage farms in the Geheyan reservoir (110.80 degrees-111.22 degrees E, 30.35 degrees-30.48 degrees N) which located on the middle reaches of the Qingjiang River of the Yangtze River basin. Seasonal hydroacoustic surveys were conducted between April 2016 and January 2017 using a Simrad EY60 echosounder to determine the changes of fish assemblages along the density gradient of fish cages in the reservoir. Significant negative correlations between wild fish density and the density of fish cages were observed in April 2016 and January 2017. In other two seasons, we also found analogous trends. In general, the abundance of wild fish assemblages around fish cages declined resulting from increased fishing pressure in the reservoir. This study suggests that the commercial capture of indigenous fish around cage farms should be limited to protect the indigenous fish resources in reservoirs