Browsing by Author "Li, Meng"

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Activity and Metabolic Versatility of Complete Ammonia Oxidizers in Full-Scale Wastewater Treatment Systems
(2020-03-01)
Yang, Yuchun
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Daims, Holger
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Liu, Yang
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Herbold, Craig W.
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Pjevac, Petra
The recent discovery of complete ammonia oxidizers (comammox) contradicts the paradigm that chemolithoautotrophic nitrification is always catalyzed by two different microorganisms. However, our knowledge of the survival strategies of comammox in complex ecosystems, such as full-scale wastewater treatment plants (WWTPs), remains limited. Analyses of genomes and in situ transcriptomes of four comammox organisms from two full-scale WWTPs revealed that comammox were active and showed a surprisingly high metabolic versatility. A gene cluster for the utilization of urea and a gene encoding cyanase suggest that comammox may use diverse organic nitrogen compounds in addition to free ammonia as the substrates. The comammox organisms also encoded the genomic potential for multiple alternative energy metabolisms, including respiration with hydrogen, formate, and sulfite as electron donors. Pathways for the biosynthesis and degradation of polyphosphate, glycogen, and polyhydroxyalkanoates as intracellular storage compounds likely help comammox survive unfavorable conditions and facilitate switches between lifestyles in fluctuating environments. One of the comammox strains acquired from the anaerobic tank encoded and transcribed genes involved in homoacetate fermentation or in the utilization of exogenous acetate, both pathways being unexpected in a nitrifying bacterium. Surprisingly, this strain also encoded a respiratory nitrate reductase which has not yet been found in any other Nitrospira genome and might confer a selective advantage to this strain over other Nitrospira strains in anoxic conditions. IMPORTANCE The discovery of comammox in the genus Nitrospira changes our perception of nitrification. However, genomes of comammox organisms have not been acquired from full-scale WWTPs, and very little is known about their survival strategies and potential metabolisms in complex wastewater treatment systems. Here, four comammox metagenome-assembled genomes and metatranscriptomic data sets were retrieved from two full-scale WWTPs. Their impressive and-among nitrifiers-unsurpassed ecophysiological versatility could make comammox Nitrospira an interesting target for optimizing nitrification in current and future bioreactor configurations.
Assessment of molecular detection of anaerobic ammonium-oxidizing (anammox) bacteria in different environmental samples using PCR primers based on 16S rRNA and functional genes
(2017-10-01)
Han, Ping
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Kluemper, Uli
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Wong, Alex
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Li, Meng
;
Lin, Jih-Gaw
Eleven published PCR primer sets for detecting genes encoding 16S ribosomal RNA (rRNA), hydrazine oxidoreductase (HZO), cytochrome cd(1)-containing nitrite reductase (NirS), and hydrazine synthase subunit A (HzsA) of anaerobic ammonium-oxidizing (anammox) bacteria were assessed for the diversity and abundance of anammox bacteria in samples of three environments: wastewater treatment plant (WWTP), wetland of Mai Po Nature Reserve (MP), and the South China Sea (SCS). Consistent phylogenetic results of three biomarkers (16S rRNA, hzo, and hzsA) of anammox bacteria were obtained from all samples. WWTP had the lowest diversity with Candidatus Kuenenia dominating while the SCS was dominated by Candidatus Scalindua. MP showed the highest diversity of anammox bacteria including C. Scalindua, C. Kuenenia, and Candidatus Brocadia. Comparing different primer sets, no significant differences in specificity for 16S rRNA gene could be distinguished. Primer set CL1 showed relatively high efficiency in detecting the anammox bacterium hzo gene from all samples, while CL2 showed greater selectivity for WWTP samples. The recently reported primer sets of the hzsA gene resulted in high efficiencies in detecting anammox bacteria while nirS primer sets were more selective for specific samples. Results collectively indicate that the distribution of anammox bacteria is niche-specific within different ecosystems and primer specificity may cause biases on the diversity detected.
Enhanced crystallization and stability of perovskites by a cross-linkable fullerene for high-performance solar cells
(2016)
Li, Meng
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Chao, Yi-Hsiang
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Kang, Tin
;
Wang, Zhao-Kui
;
Yang, Ying-Guo
Organic-inorganic halide perovskite solar cells (PSCs) still suffer from the issues of poor reproducibility and inferior stability despite their considerable increase in efficiency. Here, we demonstrate planar PSCs with simultaneously improved device characteristics and stability by introducing a cross-linkable [6,6]-phenyl-C-61-butyric styryl dendron ester (PCBSD) into CH3NH3PbIxCl3-x perovskites. The cross-linkable merit of C-PCBSD can enhance the crystallization of perovskites and address the issue of low electron extraction efficiency. In addition, the anti-solvent network of C-PCBSD facilitates the sequential solution process and prevents washing by the solvent used in the upper layer. The C-PCBSD network resisted the moisture incursion and protected the interfaces from erosion, and it passivated the voids or pinholes generated in the bulk active layer. As a result, an outstanding PSC with a power conversion efficiency of 17.21% is achieved with evidently improved cell stability.
Graphdiyne-modified cross-linkable fullerene as an efficient electron-transporting layer in organometal halide perovskite solar cells
(2018-01-01)
Li, Meng
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Wang, Zhao-Kui
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Kang, Tin
;
Yang, Yingguo
;
Gao, Xingyu
Interface engineering resulting in good contact, enhanced transport capability, and matched energy levels is indispensable and critical for the development of high-performance planar perovskite solar cells (PSCs). Here, we report an excellent electron-transporting layer (ETL) that can simultaneously enhance the stability and efficiency of n-i-p planar PSCs. Large pi-conjugated graphdiyne (GD) was introduced into cross-linkable fullerene [6,6]-phenyl-C61-butyric styryl dendron ester (PCBSD) to improve the film orientation. Raman spectroscopy and 2D grazing incidence X-ray diffraction (GIXRD) measurements revealed that a strong pi-pi stacking interaction occurred between GD and cross-linkable PCBSD (C-PCBSD), generating a face-on stacked composite film. The orientated C-PCBSD: GD films was favorable for the growth and crystallization of the subsequent perovskite films and provided the merits of superior electron mobility, efficient charge extraction and energy-level tailoring. In addition, the thermally annealed C-PCBSD: GD film provided an adhesive film network with sufficient solvent resistance. Consequently, the perovskite devices delivered a power conversion efficiency of 20.19% with obviously improved cell stability. This indicates a potential application of GD-modified cross-linkable fullerene as an ETL in n-i-p structure PSCs. The finding opens a new route to deposit the fullerene films with ordered orientation by 2D materials with large pi-conjugation, and thus to control the subsequent perovskite crystallization.
Metagenomic and metatranscriptomic analyses reveal activity and hosts of antibiotic resistance genes in activated sludge
(2019-08-01)
Liu, Zongbao
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Klumper, Uli
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Liu, Yang
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Yang, Yuchun
;
Wei, Qiaoyan
Wastewater treatment plants (WWTPs) are a source and reservoir for subsequent spread of various antibiotic resistance genes (ARGs). However, little is known about the activity and hosts of ARGs in WWTPs. Here, we utilized both metagenomic and metatranscriptomic approaches to comprehensively reveal the diversity, abundance, expression and hosts of ARGs in activated sludge (AS) from three conventional WWTPs in Taiwan. Based on deep sequencing data and a custom-made ARG database, a total of 360 ARGs associated with 24 classes of antibiotics were identified from the three AS metagenomes, with an abundance range of 7.06 x 10(-1)-1.20 x 10(-4) copies of ARG/copy of 16S rRNA gene. Differential coverage binning analysis revealed that > 22 bacterial phyla were the putative hosts of the identified ARGs. Surprisingly, genus Mycobacterium and family Burkholderiaceae were observed as multi-drug resistant harboring 14 and 50 ARGs. Metatranscriptome analysis showed 65.8% of the identified ARGs were being expressed, highlighting that ARGs were not only present, but also transcriptionally active in AS. Remarkably, 110 identified ARGs were annotated as plasmid-associated and displayed a close to two-fold increased likelihood of being transcriptionally expressed compared to those ARGs found exclusively within bacterial chromosomes. Further analysis showed the transcript abundance of aminoglycoside, sulfonamide, and tetracycline resistance genes was mainly contributed by plasmid-borne ARGs. Our approach allowed us to specifically link ARGs to their transcripts and genetic context, providing a comprehensive insight into the prevalence, expression and hosts of ARGs in AS. Overall, results of this study enhance our understanding of the distribution and dissemination of ARGs in WWTPs, which benefits environmental risk assessment and management of ARB and ARGs.
Perovskite Grains Embraced in a Soft Fullerene Network Make Highly Efficient Flexible Solar Cells with Superior Mechanical Stability
(2019-06-01)
Li, Meng
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Yang, Ying-Guo
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Wang, Zhao-Kui
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Kang, Tin
;
Wang, Qiong
Halide perovskite films processed from solution at low-temperature offer promising opportunities to make flexible solar cells. However, the brittleness of perovskite films is an issue for mechanical stability in flexible devices. Herein, photo-crosslinked [6,6]-phenylC(61)-butyric oxetane dendron ester (C-PCBOD) is used to improve the mechanical stability of methylammonium lead iodide (MAPbI(3)) perovskite films. Also, it is demonstrated that C-PCBOD passivates the grain boundaries, which reduces the formation of trap states and enhances the environmental stability of MAPbI(3). Thus, MAPbI(3) perovskite solar cells are prepared on solid and flexible substrates with record efficiencies of 20.4% and 18.1%, respectively, which are among the highest ever reported for MAPbI(3) on both flexible and solid substrates. The result of this work provides a step improvement toward stable and efficient flexible perovskite solar cells.
Specific and effective detection of anammox bacteria using PCR primers targeting the 16S rRNA gene and functional genes
(2020-09-10)
Yang, Yuchun
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Li, Meng
;
Li, Hui
;
Li, Xiao-Yan
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Lin, Jih-Gaw