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Herein, we report that Co(II)-doped g-C3N4 can efficiently trigger peracetic acid (PAA) oxidation of various sulfonamides (SAs) in a wide pH range. Quite different from the traditional radical-generating or typical nonradical-involved (i.e., singlet oxygenation and mediated electron transfer) catalytic systems, the PAA activation follows a novel nonradical pathway with unprecedented high-valent cobalt-oxo species [Co(IV)] as the dominant reactive species. Our experiments and density functional theory calculations indicate that the Co atom fixated into the nitrogen pots of g-C3N4 serves as the main active site, enabling dissociation of the adsorbed PAA and conversion of the coordinated Co(II) to Co(IV) via a unique two-electron transfer mechanism. Considering Co(IV) to be highly electrophilic in nature, different substituents (i.e., five-membered and six-membered heterocyclic moieties) on the SAs could affect their nucleophilicity, thus leading to the differences in degradation efficiency and transformation pathway. Also, benefiting from the selective oxidation of Co(IV), the established oxidative system exhibits excellent anti-interference capacity and achieves satisfactory decontamination performance under actual water conditions. This study provides a new nonradical approach to degrade SAs by efficiently activating PAA via heterogeneous cobalt-complexed catalysts.

Batch experiments were conducted to study bioelectrochemical enhancement of the anaerobic digestion (AD) of alkaline-pretreated sewage sludge in microbial electrolysis cell (MEC) in the presence or absence of phosphate buffer solution (PBS). Experimental results showed that the maximum methane production rate was increased from 0.18 mL-CH4/(mLreactor·d) (control) to 0.2 mL-CH4/(mLreactor·d) in the presence of PBS and cumulative methane production was 1.4-fold higher than that of control. The initial concentrations of SCOD, protein, polysaccharide and VFAs in the presence of PBS were slightly higher than those of control, suggesting that PBS might facilitate the release of organics into mixed liquor. The microbial community analysis results showed that the microbial community with PBS had higher diversity and Bacteroidetes and Firmicutes were the two most abundant phyla in the communities. Moreover, the PBS addition could enhance the growth of aceticlastic methanogens (Methanosaeta) and inhibit a portion of hydrogenotrophic methanogens (Methanobacterium), possibly due to the different cell wall composition.

The growing applications of carbon nanomaterials (CNMs) are speculated to exert potential risks to aquatic ecosystems. However, little is known about the response of aquatic microalgae to surface modified nanodiamonds (NDs), which could limit the safer design and scientific assessment for further application. Here, we comprehensively integrated phenotypic and transcriptional analyses to investigate the response of Chlorella pyrenoidosa to both graphitized nanodiamonds (GNDs) and oxidized nanodiamonds (ONDs). Results indicated that 50 mg L−1 GNDs could induce higher growth inhibition with severe organelle damage and oxidative stress than the OND treatment. Intriguingly, extracellular polymeric substances (EPSs) stimulated by OND exposure alleviated the adverse effects. Meanwhile, the conventional global molecular response to surface modified NDs was meticulously disclosed to fill in the knowledge gap. Additionally, the photosynthetic mechanism, amino acid synthesis, protein synthesis and protein export were further investigated under OND treatment, confirming a positive correlation for the crucial strategy to mitigate the negative effect. The underlying mechanism response to GNDs/ONDs has been thoroughly and completely revealed, providing a novel insight for the estimation of ND surface modification and the apperception of aquatic environmental risk.

In lignocellulose-to-hydrogen bioconversion, reducing the concentration of chemical agents in pretreatment is of great interest. In this study, rice straw (RS) pretreated at reduced NaOH and urea (NU) concentrations was evaluated. Results showed that the composition of RS exhibited excellent pretreatment performance at a reduced concentration of NU. When the concentration of NaOH was decreased to 3 wt% in combination with 6 wt% urea, the lignin was reduced by 59.52% with a cellulose and hemicellulose loss of less than 17%. Moreover, extending the pretreatment time at a low concentration of NU could effectively promote the biodegradability of RS. Upon fermentation by Thermoanaerobacterium thermosaccharolyticum M18 for H2 production, the H2 production increased up to 213.06 mL/g with a substrate treated by 3 wt% NaOH/6 wt% urea at low solid loading for 15 d, which was 16.31% higher than the counterpart subjected to a 7 wt% NaOH/12 wt% urea pretreatment. The present results suggest the NU pretreatment can be carried out at low concentrations to improve the conversion of RS into bio-H2 production.

Methane, a potent greenhouse gas of global importance, has traditionally been considered as an end product of microbial methanogenesis of organic matter. Paradoxically, growing evidence has shown that some microbes, such as cyanobacteria, algae, fungi, purple non-sulfur bacteria, and cryptogamic covers, produce methane in oxygen-saturated aquatic and terrestrial ecosystems. The non-methanogenesis process could be an important potential contributor to methane emissions. This systematic review summarizes the knowledge of microorganisms involved in the non-methanogenesis process and the possible mechanisms of methane formation. Cyanobacteria-derived methane production may be attributed to either demethylation of methyl phosphonates or linked to light-driven primary productivity, while algae produce methane by utilizing methylated sulfur compounds as possible carbon precursors. In addition, fungi produce methane by utilizing methionine as a possible carbon precursor, and purple non‐sulfur bacteria reduce carbon dioxide to methane by nitrogenase. The microbial methane distribution from the non-methanogenesis processes in aquatic and terrestrial environments and its environmental significance to global methane emissions, possible mechanisms of methane production in each open water, water-to-air methane fluxes, and the impact of climate change on microorganisms are also discussed. Finally, future perspectives are highlighted, such as establishing more in-situ experiments, quantifying methane flux through optimizing empirical models, distinguishing individual methane sources, and investigating nitrogenase-like enzyme systems to improve our understanding of microbial methane emission from the non-methanogenesis process.

Bio-H2, produced from lignocellulosic biomass or organic wastewater, is an ideal future energy candidate due to its feature of renewability and sustainability. In order to uncover the mechanisms of the reducing agent of l -cysteine in bio-H2 production process, effects of l -cysteine on oxidation–reduction potential (ORP), cell growth, H2 yield by Ethanoligenens harbinense were investigated. Meanwhile, effects of l -cysteine on the expression of genes such as [FeFe]-hydrogenase (hydA), acetate kinase (AK), alcohol dehydrogenase (ADH), and lactate dehydrogenase (LDH) were analysed by quantitative reverse transcription PCR (qRT-PCR). The maximum H2 yield of 1.88 mol-H2/mol-glucose and dry cell weight of 0.92 g/L, which were about 1.57 and 1.51 folds of that of negative control, were obtained with supplementation of 800 mg/L l -cysteine. The experimental results indicated that the supplementation of l -cysteine at a suitable dosage (

Currently, the complex mechanism of lipid production in microalgal cells is still unclear, and the platform suitable for microalgal genetic transformation is urgent to be established. In this study, the whole genome of a lipid-rich microalgal mutant strain Scenedesmus sp. Z-4 and a lipid-poor wild strain Scenedesmus sp. MC-1 were sequenced, and results revealed that the sequences of 1,256 genes were changed and 148 differential genes related to glucose and lipid metabolism were identified. Especially, gene differentiation of acetyl-CoA carboxylase (ACCase) and phosphoenolpyruvate carboxylase (PEPC) in mutant strain Z-4 and wild strain MC-1, which played key roles in lipid synthesis, were evaluated. Furthermore, to investigate whether mutated ACCase and PEPC genes affect the lipid production, two genes from mutant strain Z-4 were transformed into the expression system of wild strain MC-1. Nine transformants with higher lipid content were successfully obtained, in which the optimal transformant with 28.6% more intracellular lipid than wild strain MC-1 was isolated by overexpression of mutated ACCase gene, demonstrating the important role of ACCase in lipid accumulation of microalgal cells. These results could provide a better understanding of the superior lipid production of mutant strain Scenedesmus sp. Z-4.

The performance and microbial community succession of a 36 L working volume plug flow reactor was evaluated for treated cattle manure at an organic loading rate of 2.67 g-TS/L/day, a temperature of 38 °C ± 1 °C, and a hydraulic retention time of 18 days. A reflux of acidizing fluid effectively enhanced anaerobic digestion performance and promoted optimization of microbial community structure. The average biogas volume production rate was 1.08 L biogas/L reactor, which was 116.5% higher than the control without reflux of acidizing fluid. The specific qmethane production yield and methane content reached 0.204 L/g VS and 70%. Moreover, methane yield achieved 0.34 m3/kg removal COD with a COD removal of about 70.56%. The bacteria genera Christensenellaceae, Bacteroidales, vadinBC27, Ruminococcaceae and Treponema_2 were further enriched. Methanosarcina became the dominant methanogen in the whole PFR operation process. This study offers new opportunities for producing renewable energy from enhanced cattle manure biodegradability.

Background H2–ethanol-coproducing bacteria, as primary fermenters, play important roles in the microbiome of bioreactors for bioenergy production from organic wastewater or solid wastes. Ethanoligenens harbinense YUAN-3 is an anaerobic ethanol–H2-fermenting bacterium. Ethanol is one of the main end-products of strain YUAN-3 that influence its fermentative process. Until recently, the molecular mechanism of metabolic regulation in strain YUAN-3 during ethanol accumulation has still been unclear. This study aims to elucidate the metabolic regulation mechanisms in strain YUAN-3, which contributes to effectively shape the microbiome for biofuel and bioenergy production from waste stream. Results This study reports that ethanol stress altered the distribution of end-product yields in the H2–ethanol-coproducing Ethanoligenens harbinense strain YUAN-3. Decreasing trends of hydrogen yield from 1888.6 ± 45.8 to 837 ± 64.7 mL L−1 and acetic acid yield from 1767.7 ± 45 to 160.6 ± 44.7 mg L−1 were observed in strain YUAN-3 with increasing exogenous ethanol (0 mM–200 mM). However, the ethanol yield of strain YUAN-3 increased by 15.1%, 30.1%, and 27.4% in 50 mM, 100 mM, and 200 mM ethanol stress, respectively. The endogenous ethanol accounted for 96.1% (w/w) in liquid end-products when exogenous ethanol of 200 mM was added. The molar ratio of ethanol to acetic acid increased 14 times (exogenous ethanol of 200 mM) compared to the control. iTRAQ-based quantitative proteomic analysis indicated that 263 proteins of strain YUAN-3 were differentially expressed in 50 mM, 100 mM, and 200 mM of exogenous ethanol. These proteins are mainly involved in amino acid transport and metabolism, central carbon metabolism, and oxidative stress response. Conclusion These differentially expressed proteins play important roles in metabolic changes necessary for growth and survival of strain YUAN-3 during ethanol stress. The up-regulation of bifunctional acetaldehyde-CoA/alcohol dehydrogenase (ADHE) was the main reason why ethanol production was enhanced, while hydrogen gas and acetic acid yields declined in strain YUAN-3 during ethanol stress. This study also provides a new approach for the enhancement of ethanologenesis by H2–ethanol-coproducing bacteria through exogenous ethanol addition.

Glucose and xylose co-fermentation is crucial to maximize hydrogen yield from waste lignocellulose. In this study, cell growth, sugar consumption, and hydrogen production profiles of Thermoanaerobacter thermosaccharolyticum W16 feeding with a range of glucose and xylose were experimental investigated coupled with kinetic analysis. Results showed although T. thermosaccharolyticum W16 could use both glucose and xylose for hydrogen production, a maximum cell growth rate of 0.27 g/L/h and hydrogen production rate of 14.53 mmol/L/h was found with glucose as sole substrate, the value was 92.8% and 49.8% higher than using xylose as the only carbon source. Further interpolation analysis and experimental demonstration suggested when glucose content in the mixed substrate higher than 58.2%, the inhibitory effect on xylose utilization was increased, but when glucose concentration fell below 21.7%, its utilization will be subject to a certain degree of feedback inhibition. Coupling experimental results with kinetic analysis in this study provides a powerful evidence to further develop the potential of T. thermosaccharolyticum W16 as a biocatalyst for hydrogen production from lignocellulosic biomass.

In the present work, with corn stover hydrolysate as the substrate, an efficient hydrogen-producing thermophile, Thermoanaerobacterium thermosaccharolyticum W16, was added to three kinds of seed sludge (rotten corn stover (RCS), cow dung compost (CDC), and sludge from anaerobic digestion (SAD)) to investigate the effect of bioaugmentation on thermophilic hydrogen production. Batch test results indicate that the bioaugmentation with a small amount of the strain T. thermosaccharolyticum W16 (5% of total microbes) increased the hydrogen yield to varying degrees (RCS: from 8.78 to 9.90 mmol H2/g utilized sugar; CDC: from 8.18 to 8.42 mmol H2/g utilized sugar; SAD: from 8.55 to 9.17 mmol H2/g utilized sugar). The bioaugmentation process also influenced the soluble metabolites composition towards more acetate and less butyrate production for RCS, and more acetate and less ethanol accumulation for SAD. Microbial community analysis indicates that Thermoanaerobacterium spp. and Clostridium spp. dominated microbial community in all situations and might be mainly responsible for thermophilic hydrogen generation. For RCS and SAD, the bioaugmentation obviously increased the relative abundance of the strain T. thermosaccharolyticum W16 in microbial community, which might be the main reason for the improvement of hydrogen production in these cases.

The lipid production and nutrients removal of Scenedesmus sp. in non-sterile domestic wastewater were investigated in the present study. Compared with secondary effluent, primary effluent was more appropriate substrate for algal growth, and the biomass concentration and lipid yield reached 0.69 ± 0.02 g L−1 and 166.7 ± 8.3 mg L−1, respectively. Ultrasonic exposure significantly enhanced the lipid yield and wastewater treatment performance. The biomass and lipid accumulation increased to 1.56 ± 0.07 g L−1 and 240 ± 9.2 mg L−1 at the optimum ultrasonic treatment frequency of 18 Hz, power of 20 W and time of 10 min. The maximum TN and TP removal rates reached 96.8% and 97.7%, respectively. Microbial community analysis revealed that the ultrasonic treatment markedly affected the microbial communities, which can accelerate the formation of favorable microbial community structure. Gemmobacter and Porphyrobacter were identified as key bacteria under ultrasonic condition, and their relative abundances were 38.7% and 19.1%, respectively. This research showed the efficiency of ultrasonic treatment in promoting algal lipid yield and domestic wastewater treatment.

In this study, a novel, single-chamber bioelectrochemical system (BES) with stacked modules was developed to improve azo dye decolorization. The decolorization extent of BES with three modules (80.3 ± 3.1%) was about 15% and 33% higher than that with two modules (65.6 ± 4.5%) and one module (47.1 ± 3.9%) at an influent Acid Orange 7 (AO7) loading rate of 250 g m−3 d−1, demonstrating the feasibility of enhanced decolorization in scale-up BES through increasing the number of stacked modules. Moreover, the contribution of each module to dye decolorization, chemical oxygen demand (COD) removal and volatile fatty acids (VFAs) changes, showed the sequential utilization of pollutants in the stacked BES. Furthermore, analysis of the microbial communities showed that Pseudomonas, Geobacter, Comamonas, Meniscus, Bellilinea, Achromobacter, and Paludibacter were significantly enriched and resulted in the specific microbial community structures of the biocathode, meanwhile Geobacter and Acinetobacter were enriched in the microbial community of the bioanode, which mainly contributed to the electron transfer and/or azo dye decolorization. The results of this study demonstrate the potential of stacked BES for the accelerated deployment of large-scale BES applications for the treatment of refractory waste streams such as azo dye-bearing wastewater.

Antibiotics can exert selective pressures on sludge as well as affect the emergence and spread of antibiotic resistance genes (ARGs). However, the underlying mechanisms of ARGs transfers are still controversial and not fully understood in sludge system. In present study, two anaerobic sequence batch reactors (ASBR) were constructed to investigate the development of ARGs exposed to two sulfonamide antibiotics (SMs, sulfadiazine SDZ and sulfamethoxazole SMX) with increasing concentrations. The abundance of corresponding ARGs and total ARGs obviously increased with presence of SMs. Functional analyses indicated that oxidative stress response, signal transduction and type IV secretion systems were triggered by SMs, which would promote ARGs transfers. Network analysis revealed 18 genera were possible hosts of ARGs, and their abundances increased with SMs. Partial least-squares path modeling suggested functional modules directly influenced mobile genetic elements (MGEs) as well as the ARGs might be driven by both functional modules and bacteria community, while bacteria community composition played a more key role. Sludge with refractory antibiotics (SDZ) may stimulate the relevant functions and shift the microbial composition to a greater extent, causing more ARGs to emerge and spread. The mechanisms of ARGs transfers are revealed from the perspective of functional modules and bacterial community in sludge system for the first time, and it could provide beneficial directions, such as oxidative stress reduction, cellular communication control, bacterial composition directional regulation, for ARGs spread controlling in the future.

The medium chain fatty acids (MCFAs) produced from organic wastes can replace part fossil-fuel-based products to promote the sustainable development of economy and environment. However, the selection and collocation of feedstocks for MCFAs production are lack of reference basis. This study thereby aimed to investigate how the commonly used electron donor (ED) and substrate configuration affect MCFAs synthesis and then obtain the optimal substrate composition. It was found that the optimized ratios for ethanol/acetate, lactate/acetate, and ethanol/lactate/acetate were 3/1, 2/1, and 2/1/1, respectively, and the optimal substrate concentration was 400 mM C. Combining ethanol and lactate as co-EDs effectively concentrated substrate-carbon-flow (increased by 20–28% than sole ED) on MCFAs synthesis by promoting the elongation of butyrate and reutilization of by-products. As a result, the higher MCFAs yield of 646.22 mg COD/g COD and selectivity of 67.72% were obtained from co-EDs than those from sole ED. Moreover, the key functional bacteria enriched under different ED were also discrepant, which were Clostridium sensu stricto for ethanol, Corynebacterium for lactate, and Veillonella and Oscillibacter for ethanol-lactate, respectively. This study provided a basic but significant reference for the scale-up MCFAs production.

In this study, an innovative approach was proposed based on the implement of biochar derived from residue cornstalk left after anaerobic bio-hydrogen production (RCA-biochar) to improve direct bio-hydrogen production from anaerobic fermentation of cornstalk. The bio-hydrogen production potential and maximum bio-hydrogen production rate increased from 156.2 to 286.1 mL H2/g substrate and 3.5 to 5.7 mL H2/g substrate/h, respectively, following the added RCA-biochar increased from 2.5 to 15.0 g/L. Cornstalk chemical component analysis showed the cellulose and hemicellulose content decreased by 17.9–33.7% and 14.4–25.2%, and lignin content increased by 20.3–42.8%, respectively, after 96 h anaerobic fermentation with RCA-biochar 2.5–15.0 g/L. Further analyses revealed that RCA-biochar not only provided more specific surface area for hydrogen-producing bacteria attachment, but also promoted the cellulolytic enzyme activity, thereby resulted in increased substrate conversion to bio-hydrogen. The findings obtained in this study may provide supports for effective and sustainable lignocellulosic bio-hydrogen production in the future.

Anthropogenic nutrients released into water induce eutrophication and threaten aquatic life and human health. In this study, an Fe anode coagulation cell with nitrification and denitrification biocathodes was constructed for power generation and algae and nutrient removal. The nitrification and denitrification biocathodes achieved maximum power densities of 6.0 and 6.6 W/m3, respectively. The algae (99.2 ± 0.5%), phosphate (97.4 ± 0.6%), and ammonia (23.1 ± 0.2%) were removed by a spontaneous electrocoagulation process in the anode chamber. In the nitrification biocathode chamber, 95.3 ± 1.4% of the ammonia was oxidized within 6 h, and 88.2 ± 2.5% of the nitrate was removed in 10 h in the denitrification biocathode chamber. The microbial community analysis revealed that ammonia removal was attributed to nitrifying bacteria, including Acinetobacter sp., Phycisphaera sp., and Nitrosomonas sp., and the dominant denitrifying bacteria in the denitrifying biocathode chamber were Planococcus sp., Exiguobacterium sp., and Lysinibacillus sp. In this study, the combination of Fe anodes and biocathodes is shown to afford an efficient method for the simultaneous algae and nutrient removal and power generation.

Sulfate dependent ammonium oxidation (Sulfammox) is a potential microbial process coupling ammonium oxidation with sulfate reduction under anaerobic conditions, which provides a novel link between nitrogen and sulfur cycle. Recently, Sulfammox was detected in wastewater treatments and was confirmed to occur in natural environments, especially in marine sediments. However, knowledge gaps in the mechanism of Sulfammox, functional bacteria, and their metabolic pathway, make it challenging to estimate its environmental significance and potential applications. This review provides an overview of recent advances in Sulfammox, including possible mechanisms, functional bacteria, and main influential factors, and discusses future challenges and opportunities. Future perspectives are outlined and discussed, such as exploration of microbial community structure and metabolic pathways, possible interactions with other microbes, environmental significance, and potential applications for nitrogen and sulfate removal, to inspire more researches on the Sulfammox process.

To reduce start-up time and enhance hydrogen production efficiency, a sequential immobilization and deoxygenization (SIDO) strategy for hydrogen production was investigated in continuous-flow moving bed biofilm reactors (MBBRs). The pre-immobilization process accelerated the initial enrichment of hydrogen-producing bacteria (HPB) and promoted the biofilm formation, which contribute to higher hydrogen production efficiency in SIDO-MBBRs compared to a non-immobilized reactor. A similar deoxygenization effect was achieved by inoculation with Pseudomonas aeruginosa compared with N2 sparging, and the P. aeruginosa pre-immobilized MBBR (Pse-MBBR) showed a higher H2 yield in the initial stage of operation. Microbial community analysis found a higher abundance of putative HPB in the range of 82.82-96.56%, with the predominant populations in the SIDO-MBBR assigned to genera Clostridium and Enterobacter. The results suggest that the SIDO-MBBR is an effective approach for rapid recruitment of HPB and start-up of fermentative hydrogen production.

Clostridium tyrobutyricum is a promising microbial cell factory to produce biofuels. In this study, an uptake hydrogenase (hyd2293) from Ethanoligenens harbinense was overexpressed in C. tyrobutyricum and significantly affected the redox reactions and metabolic profiles. Compared to the parental strain (Ct-WT), the mutant strain Ct-Hyd2293 produced ~34% less butyrate, ~148% more acetate, and ~11% less hydrogen, accompanied by the emerging genesis of butanol. Comparative transcriptome analysis revealed that 666 genes were significantly differentially expressed after the overexpression of hyd2293, including 82 up-regulated genes and 584 down-regulated genes. The up-regulated genes were mainly involved in carbohydrate and energy metabolisms while the down-regulated genes were distributed in nearly all pathways. Genes involved in glucose transportation, glycolysis, different fermentation pathways and hydrogen metabolism were studied and the gene expression changes showed the mechanism of the metabolic flux redistribution in Ct-Hyd2293. The overexpression of uptake hydrogenase redirected electrons from hydrogen and butyrate to butanol. The key enzymes participating in the energy conservation and sporulation were also identified and their transcription levels were generally reduced. This study demonstrated the transcriptomic responses of C. tyrobutyricum to the expression of a heterologous uptake hydrogenase, which provided a better understanding of the metabolic characteristics of C. tyrobutyricum and demonstrated the potential role of redox manipulation in metabolic engineering for biofuel productions.

Background Ethanol-type fermentation, one of the fermentation types in mixed cultures of acidogenesis with obvious advantages such as low pH tolerance and high efficiency of H2 production, has attracted widespread attentions. pH level greatly influences the establishment of the fermentation of carbohydrate acidogenesis by shaping community assembly and the metabolic activity of keystone populations. To explore the adaptation mechanisms of ethanol-type fermentation to low pH, we report the effects of initial pH on the physiological metabolism and transcriptomes of Ethanoligenens harbinense—a representative species of ethanol-type fermentation. Results Different initial pH levels significantly changed the cell growth and fermentation products of E. harbinense. Using transcriptomic analysis, we identified and functionally categorized 1753 differentially expressed genes (DEGs). By mining information on metabolic pathways, we probed the transcriptional regulation of ethanol–H2 metabolism relating to pH responses. Multiple pathways of E. harbinense were co-regulated by changing gene expression patterns. Low initial pH down-regulated the expression of cell growth- and acidogenesis-related genes but did not affect the expression of H2 evolution-related hydrogenase and ferredoxin genes. High pH down-regulated the expression of H2 evolution- and acidogenesis-related genes. Multiple resistance mechanisms, including chemotaxis, the phosphotransferase system (PTS), and the antioxidant system, were regulated at the transcriptional level under pH stress. Conclusions Ethanoligenens adapted to low pH by regulating the gene expression networks of cell growth, basic metabolism, chemotaxis and resistance but not H2 evolution-related genes. Regulation based on pH shifts can represent an important approach to establish and enhance ethanol-type fermentation. The complete gene expression network of ethanol fermentative bacteria for pH response provides valuable insights into the acidogenic fermentation, and offers an effective regulation strategy for the sustainable energy recovery from wastewater and solid waste.

In the present study, we exposed Procambarus clarkii to different doses (0, 1, and 10 mg/L) of diclofenac (DCF). Meanwhile, we investigated the effects of exposure to DCF on intestinal histology, antioxidant defense, and microbial communities in P. clarkii. The results showed DCF caused histological changes in the intestines. Additionally, DCF induced significant changes in the expression of antioxidant genes including Mn-sod, cat, gst, and gpx. High-throughput sequencing of 16 S rRNA gene revealed DCF changed the diversity, richness, and composition of intestinal microbial communities. The relative abundances of the predominant phyla Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria showed significant changes at the phylum level after treatment with DCF. At the genus level, the most predominant genera with marked differences in abundance were Lucibacterium, Shewanella, Bacteroides, Anaerorhabdus, Aeromonas, Acinetobacter, Clostridium XlVb, Arcobacter, Bosea, and so on. To conclude, treatment with DCF could cause intestinal histological damage, induce significant changes of the expression of intestinal antioxidant genes, and impact the composition of intestinal microbiota in P. clarkii. This research will provide novel insights into the toxic effects of DCF on aquatic crustaceans.

Micro-aeration is an effective tool that helps integrated autotrophic and heterotrophic denitrification process to withstand high sulfide concentration by making heterotrophic sulfide-oxidizing nitrate-reducing bacteria (h-soNRB) prevail. For further understanding of the dominance of h-soNRB, Pseudomonas C27 was selected as the typical bacterium and its metabolic characteristics responding to sulfide and oxygen stimulation were studied. Under high sulfide concentration condition, addition of trace oxygen led to a two-stage sulfide oxidation process, and sulfide oxidation rate in the first stage was 1.4 times more than that under anaerobic condition. According to transcriptome analysis, the pdo gene significantly up-regulated 2.36 and 2.57 times with and without oxygen under stimulation of high sulfide concentration. Additionally, two possible enhanced sulfide removal pathways coping with high sulfide concentration, namely sqr-cysI-gpx-gor-glpE and cysK-gshA-gshB-pdo-glpE, caused by oxygen were proposed in Pseudomonas C27. These findings provide a theoretical basis for locating high-efficiency sulfur oxidase in h-soNRB.

Photo-fermentative hydrogen production, the new energy production alternative, was greatly enhanced by formed biofilm. To understand the mechanism of enhancement, the intracellular proteome and extracellular polymeric substance (EPS)ii EPS: extracellular polymeric substanceiiPFHP: Photo-fermentative hydrogen productioniiiPFB: photo-fermentative bacteriaivQS: quorum sensingvCLSM: Confocal laser scanning microscopyviCR: Control reactorviiBR: Biofilm reactorviiiTEM: Transmission electron microscopeixXPS: X-ray photoelectron spectroscopyxFTIR: Fourier transform infrared spectroscopyxiSM: Supplementary materialsxiiDEPs: Differentially expressed proteinsxiiiTCA cycle: Tricarboxylic acid cyclexivGO: Gene ontologyxvKEGG: Kyoto encyclopedia of genes and genomes during biofilm formation were investigated in this work. Experimental results indicated that a possible and effective altered system could transfer light to hydrogen. Proteins were significantly regulated, for example those related with nitrogenase, flagellin, EPS transportation and DNA duplication were up-regulated while those concerned photosystem were down-regulated. It revealed these changes of proteins contributed to positive activity of key enzymes, improved communication system and increased total light utilization efficiency thus leading to enhanced capacity of hydrogen production. Besides above metabolic changes inside the cells, EPS secreted by the bacteria played an important role in hydrogen production and its yield decided the release of hydrogen. When EPS descended to a lower concentration during biofilm formation, it meant carbon source for EPS synthesis was reduced, and more energy and reducing power could be transferred into hydrogen energy. More importantly, this work found that composition and structure of EPS were efficiently influenced by the formation of biofilm, such as benzene and O-H structure, secondary protein structure and the kinds of protein, which were important to stable biofilm and efficient hydrogen production. Therefore, final hydrogen yield was improved by altered protein and EPS resulted from biofilm formation. This study demonstrated that formation of biofilm is an efficient, ecological and attracting way to the future bio-hydrogen production.

Minimum inhibition concentration (MIC) of antibiotic is an effective value to ascertain the agent and minimum dosage of inhibiting bacterial growth. However, current techniques to determine MIC are labor intensive and time-consuming, and require skilled operator and high initial concentration of bacteria. To simplify the operation and reduce the time of inhibition test, we developed a microfluidic system, containing a concentration generator and sub-micro-liter chambers, for rapid bacterial growth and inhibition test. To improve the mixing effect, a micropillar array in honeycomb-structure channels is designed, so the steady concentration gradient of amoxicillin can be generated. The flanged chambers are used to culture bacteria under the condition of continuous flow and the medium of chambers is refreshed constantly, which could supply the sufficient nutrient for bacteria growth and take away the metabolite. Based on the microfluidic platform, the bacterial growth with antibiotic inhibition on chip can be quantitatively measured and MIC can be obtained within six hours using low initial concentration of bacteria. Overall, this microfluidic platform has the potential to provide rapidness and effectiveness to screen bacteria and determine MIC of corresponding antibiotics in clinical therapies.

The environmental toxicity of tetracycline antibiotics to aquatic organisms has attracted increasing attention. The adverse impacts of tetracycline antibiotics on ciliates should be detailed considering the significant roles of protozoa in the microfood web in the soils and other eco-systems. This study for the first time investigated the toxicity of two typical tetracycline antibiotics, tetracycline (TC) and tetracycline hydrochloride (HTC) on two primary model ciliates, Stentor coeruleus and Stylonychia lemnae. The concentrations for 50% of maximal effect (24h‒EC50) of TC and HTC to Stentor coeruleus were 94.4 mg/L and 8.39 mg/L, respectively. Correspondingly, the 24h‒EC50 values of TC and HTC to Stylonychia lemnae were 40.1 mg/L and 14.0 mg/L, respectively. The TC and HTC inhibited the growth rates, reduced the activities of antioxidant enzymes, and damaged the ultra-structures of the tested ciliate cells, with the latter having larger impacts than the former. Based on the experimental works reported herein, the two model protozoan species were proposed to be the toxicity indicators for tetracycline antibiotics, which could work as supplements with the other existing protocols, such as Brochydanio rerio (zebrafish), Limnodrilus (a worm), Chlorogonium elongatum (a green alga) also studied herein.

Metabolic uncouplers inhibit biofilm and biofouling formation in membrane bioreactor (MBR) systems, which have been considered as a potential biofouling control alternative. To better understand the inhibitory mechanism of uncoupler on biofouling, this study investigated the impact of the uncoupler 3, 3′, 4′, 5-tetrachlorosalicylanilide (TCS) on biofilm formation of B. subtilis in different development stages. Significant reductions in both the initial bacterial attachment stage and the subsequent biofilm development stage were caused by TCS at 100 μg/L. The motility of B. subtilis in semisolid medium was inhibited by TCS, which explicitly explained the reduction in initial bacterial attachment. Meanwhile, a reduction of extracellular polymeric substance (EPS) secretion owing to TCS suggested why biofilm development was suppressed. In addition, the fluorescent materials in tight-bound EPS (TB-EPS) and loose-bound EPS (LB-EPS) of Bacillus subtilis cultured in different TCS concentrations were distinguished and quantified by three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC). The results of this study suggested that the biofilm inhibitory mechanism of the uncoupler was both a inhibition in bacterial motor ability and a reduction in EPS secretion.

An increasing interest is devoted to combined microbial electrolysis cell-anaerobic digestion (MEC-AD) system which could convert waste activated sludge into biogas. In this study series tests were initially conducted to study the effect of alkaline pretreatment on AD system and the results showed that alkaline pretreatment could promote the dissolution of organic matters in the sludge and thus improve the methane production. Then, the methane production in combined MEC-AD system fed with alkaline-pretreated sludge was investigated. The results indicated that the methane productions increased by 37% and 42% when applied voltage was 0.5 V and 0.8 V. The microbial electrochemical system strongly promoted the growth of Euryarchaeota (Methanosaeta and Methanobacterium). Meanwhile, the abundance of Paraclostridium increased from 17.9% to 38.5% when applied voltage was 0.8 V, suggesting an enhanced fermentation and acetogenesis process. The results of energy balance estimation indicated that MEC-AD system at 0.5 V could achieve higher net energy output.

The succession of fungal community, trophic mode and metabolic characteristics were evaluated in 60 days composting of swine manure by high-throughput sequencing, FUNGuild and Biolog method, respectively. The result showed that the fungal community diversity reached to the highest level (76 OTUs) in the thermophilic phase of composting, then sustained decline to 15 OTUs after incubation. There were 10 fungal function groups in the raw swine manure. Pathotroph-saprotroph fungi reached to 15.91% on Day-10 but disappeared on Day-60. Dung saprotroph-undefined saprotroph fungi grown from 0.19% to 52.39% during the treatment. The fungal community had more functional groups but the lower substrate degradation rates in the thermophilic phase. The fungal communities on Day-0 and Day-60 had the highest degradation rates of amino acids and polymers, respectively. Redundancy analysis showed that ORP (49.6%), VS/Ash (45.3%) and moisture (39.2%) were the main influence factors on the succession of fungal community in the swine manure composting process.

In order to understand the inhibitory mechanism of metabolic uncoupler in biofilm, this study investigated the effect of TCS on B. subtilis biofilm formation, flocculability, surface characteristics and thermodynamic properties. An optimal concentration of TCS, a metabolic uncoupler, was observed to substantially inhibit biofilm formation and the secretion of extracellular polymeric substances (EPS). The effect of TCS on the zeta potential and flocculability of bacterial suspension implied the addition of 100 μg L−1 TCS increased the net negative charge of cell surface which induced the reduction of B. subtilis flocculability. Meanwhile, the effects of TCS on bacterial surfacial thermodynamic properties were analyzed by the Derjaguin–Landau–Verwey–Overbeek (DLVO) and extend DLVO (XDLVO) theories. As DLVO and XDLVO predicted, the primary energy barrier between bacterial cells incubated with 100 μg L−1 TCS were increased compared to that of control, indicating that B. subtilis incubated with 100 μg L−1 TCS must consume more energy to aggregate or form biofilm.

The succession of complex internal sulfur cycles and sulfide-oxidizing bacteria community has been observed during wastewater treatment under microaerophilic conditions or denitrifying conditions. However, research on the microbial community involved in sulfur cycles under microaerophilic denitrifying conditions is scarce. In this study we characterized the dominant bacteria and microbial community structure stimulated by microaerophilic conditions in a sulfate and nitrate co-reduction system. Full denitrification was accomplished and the sulfate removal efficiency ranged from 79.93% to 96.81% for all the tested scenarios, with the degree of sulfate reduction slightly decreased with higher O 2 feeding rate. The proportion of S 0 to influent SO 4 2− was much greater at microaerophilic stages (27.5–69.2%) versus the anaerobic stage (11.1%). The peak S 0 recovery (69.2%) was achieved at O 2 = 4.0 mL/min. Illumina sequencing technology was used to characterize the bacterial community and the results indicated that Bacteroidetes , Firmicutes , Proteobacteria , Spirochaetae and Synergistetes members were dominant in microbial communities, however the variation of these dominant members across all the operating conditions did not well respond to reactor performance. Further analysis revealed that the structure of the microbial community, including community richness and evenness, might better respond to reactor performance, which deserves more research in future.

Lignocellulosic crop wastes (LCW) are refractory solid wastes that are not biodegradable at appreciable rates in most environments, causing management of LCW been environmental concerns for years. This study investigated the feasibility of low waste emission complete LCW (rice straw (RS), rice husk (RH), and corn straw (CS)) recycling through feeding to Tenebrio molitor Linnaeus larvae (mealworms) using egested frass to produce organic fertilizers. For larvae fed RS, CS, and RH plus nutrients co-diets groups, the 48-day average specific rates of LCW consumption increased by 118.09%, 155.30%, and 87.14%, respectively when compared with that of sole diet groups. The order of the feed consumption rate and conversion rate in a mealworm farm fed on the three LCWs agreed with the trend obtained with lab-scale experiments, with RS＞CS＞RH. The forty-eight days cellulose, hemicellulose, and lignin biodegradation increased by 1.48–17.61%, 4.26–11.50%, and 4.20–15.75%, respectively, for co-fed larvae. Enterococcus sp. and Erwinia sp., which previous reports have indicated are strongly associated with lignocellulose degradation, were identified in the gut microbiome of mealworms fed with RS and CS co-diets. Furthermore, the RS-fed frass quickly formed a high-quality compost within 32 days of composting, which had a germination rate ratio of 8% and 17% higher than that of WB and CS-fed frass. LCA (life cycle assessment) proved a relatively promising environmental-friendly alternative to dispose of RS, using their excreted frass for composting with low waste emissions. This study provides new insight into insect-involved crop waste utilization, and economical strategies for sustainable in situ recycling of LCWs into high-value-added products.

Tenebrio obscurus (Coleoptera: Tenebrionidae) larvae are capable of biodegrading polystyrene (PS) but their capacity for polyethylene (PE) degradation and pattern of depolymerization remains unknown. This study fed the larvae of T. obscurus and Tenebrio molitor, which have PE degrading capacity, two commercial low-density PE (LDPE) foams i.e., PE-1 and PE-2, with respective number-average molecular weights (Mn) of 28.9 and 27.3 kDa and weight-average molecular weights (Mw) of 342.0 and 264.1 kDa, over a 36-day period at ambient temperature. The Mw of residual PE in frass (excrement) of T. obscurus, fed with PE-1 and PE-2, decreased by 45.4 ± 0.4% and 34.8 ± 0.3%, respectively, while the respective decrease in frass of T. molitor was 43.3 ± 0.5% and 31.7 ± 0.5%. Data analysis showed that low molecular weight PE ( 10.0 kDa) were broken down or cleaved, indicating a broad depolymerization pattern. Mass balance analysis indicated nearly 40% of ingested LDPE was digested to CO2. Antibiotic suppression of gut microbes in T. molitor and T. obscurus larvae with gentamicin obviously reduced their gut microbes on day 15 but did not stop depolymerization because the Mn, Mw and size- average molecular weight (Mz) decreased. This confirmed that LDPE biodegradation in T. obscurus was independent of gut microbes as observed during previous PS degradation in T. molitor, suggesting that the intestinal digestive system could perform LDPE depolymerization. High-throughput sequencing revealed significant shifts in the gut microbial community during bran-fed and unfed conditions in response to LDPE feeding in both Tenebrio species. The respective predominant gut genera of Spiroplasma sp. and Enterococcus sp. were observed in LDPE-fed T. molitor and T. obscurus larvae.

Plastic biodegradation by mealworm is regarded as an emerging strategy for plastic disposal. In this study, the polystyrene (PS) and low density polyethylene (LDPE) degradation efficiency by yellow mealworms (Tenebrio molitor larvae) supplemented with bran and the effects of plastics on the gut core microbiome were explored to construct a circular and continuous reactor for plastic biodegradation in the future. The gut microbiome was also investigated with dietary shift to explore the relationship between specific diets and gut microbes. The bran plus plastic (7:1 ratio, w/w) co-diet contributed to the mealworm survival and growth. The formation of −C˭O−/−C−O− groups in the plastic-fed mealworms frass represented the oxidation process of plastic biodegradation in the mealworm gut. The changes in molecular weights (Mw, Mn and Mz) of residual PS and LDPE in mealworms frass compared with that of PS and PE feedstock confirmed the plastic depolymerization and biodegradation. Lactobacillus and Mucispirillum were significantly associated with PE + bran diet compared to bran diet and PE diet, representing the response of mealworm gut microbiome to the bran and plastic mixture was distinguished from either bran or plastics alone. The gut microbiome changed substantially with the diet shift, indicating that microbial community assembly was a stochastic process and diverse plastic-degrading bacteria might occur in the mealworm gut.

Microbial electrolysis cells (MECs) provide effective approaches for hydrogen production from wastewater and renewable biomass. Improving the efficiency of energy recovery from wastes remains a challenge. Here we report the cross-feeding interactions between the hydrogen-producing Ethanoligenens harbinense and electroactive Geobacter sulfurreducens in MECs and anaerobic fermentation using glucose as electron donor. Results showed that G. sulfurreducens could oxidize acetate produced by E. harbinense and transfer electrons extracellularly to the electrode of MECs, which also enhanced hydrogen production by E. harbinense via mitigation of metabolic feedback inhibition and enhancement of interspecies electron transfer. The defined co-cultures showed 2.5–2.9 times higher hydrogen production rates compared to the mono-cultures, while the MECs further enhanced the substrate conversion efficiency and converted electrical energy into hydrogen energy. The molar ratio of ethanol to acetic acid in co-cultured MECs doubled compared to mono-cultures, indicating that G. sulfurreducens steered the fermentation products of E. harbinense towards ethanol. The co-cultures formed dense aggregates or biofilms, in which close physical interactions by intercellular pili-like nanowire structures were observed between E. harbinense and G. sulfurreducens in the co-culture biofilms of both anode and cathode. These findings provide new insight into syntrophic interactions, beyond that previously reported on fermentative hydrogen-producing bacteria with electroactive bacteria or methanogens, and offer an effective strategy to enhance H2 production and steer metabolic products of fermentative bacteria.

Anaerobic co-digestion of a cow manure-cotton straw mixture (CCM) has been shown to promote methanogenesis, but the recalcitrant crystal structure of organic polymers in CCM hinders its hydrolysis during anaerobic digestion (AD). Here, the efficacy of different pretreatment methods based on potassium ferrate (PF) and peroxymonosulfate (PMS) was evaluated to facilitate CCM decomposition and methanogenesis during AD. The maximum lignocellulosic removal rate (62.5%), the highest volatile fatty acids (VFAs) (7769.6 mg/L), and cumulative methane yield (109.4 mL CH4/g VS) were both achieved in PF-pretreated samples after the digestion process. The dominant bacterial populations in PF-pretreated CCM were affiliated with Sideroxydans, Herbinix, Clostridium, and Smithella, which played an important role in the hydrolysis and acidification of CCM. The enrichment of Methanosarcina and Methanobacterium and highly-effective acidogenesis might account for the highest methane yield in the PF-pretreated group.

Anaerobic ammonium oxidation (anammox) is an important pathway in the nitrogen cycle and for autotrophic nitrogen removal of wastewater. However, the slow granulation or biofilm formation of anammox bacteria in a continuous-flow reactor without anammox inoculum is still a challenge. To accelerate granulation or biofilm formation, an approach of sequential immobilization and granulation of anammox (SIGA) and an internal circulation immobilized blanket (ICIB) with non-granular activated sludge inoculum was investigated. Pre-immobilizing the biofilm with carriers showed higher efficiencies of nitrite removal and enrichment of Candidatus Kuenenia than anaerobic sludge without immobilization. An ICIB with pre-immobilized anaerobic biofilm and an up-flow anaerobic sludge bed (UASB) with pre-acclimated anaerobic sludge were operated for 180 d. The ICIB reactor achieved a nitrogen removal rate of 1.11 kg·N/(m3·d) whereas the UASB reactor only obtained 0.29 kg·N/(m3·d). Illumina HiSeq sequencing of 16S rRNA gene amplicons indicated that the relative abundance of anammox bacteria (Candidatus Kuenenia, Candidatus Brocadia, and Candidatus Jettenia) achieved 42.5–50.6% in biofilm and 45.3–47.1% in granules in the ICIB reactor. By contrast, no anammox bacteria were enriched in the sludge of the UASB reactor. These findings showed that the granulation and the biofilm formation of abundant anammox bacteria occurred in a single ICIB. The anammox biofilm and internal circulation facilitate the granulation of anammox bacteria, as the planktonic anammox cells escaped from the biofilm on the carrier provides parent cells for the formation of anammox granules under suitable hydraulic shear conditions. This study provides a new strategy for a faster start-up of anammox using activated sludge inoculum based on ICIB and SIGA.

The environmental spread of antibiotic resistance genes (ARGs) from the direct application of traditional biological treatment systems for antibiotics in water is a potential public health threat. UV photolysis has been proved to be an efficient pretreatment method for antibacterial activity elimination, but the fate of antibiotic resistome in subsequent bioreactors fed with pretreated florfenicol (FLO) in synthetic wastewater is still unknown. Antibacterial activity in synthetic wastewater was effectively eliminated by UV irradiation pretreatment, and the diversity and abundance of detected ARGs in both aerobic and anaerobic bioreactors were significantly lower than those without pretreatment. Meanwhile, UV irradiation pretreatment shaped the structure and composition of sludge microbial communities in the subsequent bioreactors closer to those of the FLO-free groups. The relative abundances of Pseudomonas and Escherichia-Shigella working as the potential hosts of ARGs were significantly reduced in aerobic and anaerobic bioreactors, respectively. The significantly positive correlation between floR and intI1 and the decrease of intI1 abundance in UV photolytic pretreatment groups indicated that the horizontal transfer of floR was decreased. The study provides new insights into the effect of preferential UV photolysis as a pretreatment method on the source control of antibiotic resistome in subsequent biological treatment process.

Chemotaxis is the response ability of motile cells to chemicals gradients in environment and the migration toward higher concentration of chemoattractant or lower concentration of repellent. This mechanism is a basic nature of microorganisms to adapt to the environmental changes. The research of microbial chemotaxis is of great significance in utilizing bacteria to solve environment problems, control the pathogen infection, and develop microbial industrial projects. Microfluidic devices can realize qualitative and quantitative detection of bacterial chemotaxis. In comparison with traditional detection methods, microfluidic assay has an accurate control over bacterial microenvironment with higher sensitivity. In the past few years, the study on bacterial chemotaxis based on microfluidic assay was developed rapidly. In this paper, the microfluidic chemotaxis detectors that appeared in recent years were introduced from the aspects of chip structure, working principle and their applications. Finally, we provided insights into the challenges of bacterial chemotaxis and provided future perspectives.

This study aims at evaluating the performance and microbial community dynamics of anaerobic membrane bioreactor (AnMBR) treating antibiotic solvent wastewater at improved influent quality period. The whole process was divided into five phases according to the influent COD concentration with a fluctuated volume loading rate (VLR) ranging from 3.9 to 12.7 kg COD/(m 3 ·d). After 249 days of operation, the average COD and THF removal efficiency were 93.6% and 98.7%, respectively. The accumulation of VFA, relatively low pH, decline of biogas production and methane content were discovered at higher VLR (>10 kg COD/(m 3 ·d)). Methanomicrobiales are the major population throughout the whole running period. Methanosaetaceae showed a minor relative abundance compared both of them, while Methanobacteriales remained a minimum value. Results showed that the reactor performed an excellent pollutants removal effect because of the function of membranes even at high VLR conditions.

Background The light/dark cycle is one of the most important factors affecting the microalgal growth and lipid accumulation. Biomass concentration and lipid productivity could be enhanced by optimization of light/dark cycles, and this is considered an effective control strategy for microalgal cultivation. Currently, most research on effects of light/dark cycles on algae is carried out under autotrophic conditions and little information is about the effects under mixotrophic cultivation. At the same time, many studies related to mixotrophic cultivation of microalgal strains, even at large scale, have been performed to obtain satisfactory biomass and lipid production. Therefore, it is necessary to investigate cellular metabolism under autotrophic and mixotrophic conditions at different light/dark cycles. Even though microalgal lipid production under optimal environmental factors has been reported by some researchers, the light/dark cycle and temperature are regarded as separate parameters in their studies. In practical cases, light/dark cycling and temperature variation during the day occur simultaneously. Therefore, studies about the combined effects of light/dark cycles and temperature variation on microalgal lipid production are of practical value, potentially providing significant guidelines for large-scale microalgal cultivation under natural conditions. Results In this work, cell growth and lipid accumulation of an oleaginous microalgal mutant, Scenedesmus sp. Z-4, were investigated at five light/dark cycles (0 h/24 h, 8 h/16 h, 12 h/12 h, 16 h/8 h, and 24 h/0 h) in batch culture. The results showed that the optimal light/dark cycle was 12 h/12 h, when maximum lipid productivity rates of 56.8 and 182.6 mg L−1 day−1 were obtained under autotrophic and mixotrophic cultivation, respectively. Poor microalgal growth and lipid accumulation appeared in the light/dark cycles of 0 h/24 h and 24 h/0 h under autotrophic condition. Prolonging the light duration was unfavorable to the production of chlorophyll a and b, which was mainly due to photooxidation effect. Polysaccharide was converted into lipid and protein when the light irradiation time increased from 0 to 12 h; however, further increasing irradiation time had a negative effect on lipid accumulation. Due to the dependence of autotrophically cultured cells on light energy, the light/dark cycle has a more remarkable influence on cellular metabolism under autotrophic conditions. Furthermore, the combined effects of temperature variation and light/dark cycle of 12 h/12 h on cell growth and lipid accumulation of microalgal mutant Z-4 were investigated under mixotrophic cultivation, and the results showed that biomass was mainly produced at higher temperatures during the day, and a portion of biomass was converted into lipid under dark condition. Conclusions The extension of irradiation time was beneficial to biomass accumulation, but not in favor of lipid production. Even though effects of light/dark cycles on autotrophic and mixotrophic cells were not exactly the same, the optimal lipid productivities of Scenedesmus sp. Z-4 under both cultivation conditions were achieved at the light/dark of 12 h/12 h. This may be attributed to its long-term acclimation in natural environment. By combining temperature variation with optimal light/dark cycle of 12 h/12 h, this study will be of great significance for practical microalgae-biodiesel production in the outdoor conditions. Electronic supplementary material The online version of this article (10.1186/s13068-017-0948-0) contains supplementary material, which is available to authorized users.

In this study, a carbohydrate-rich microalga Neochloris aquatica CL-M1 was adapted to grow in swine wastewater. The effects of cultivation conditions (i.e., temperature, light intensity or N/P ratio) on COD/nutrients removal and carbohydrate-rich biomass production were investigated. The results indicate that the highest COD removal (81.7%) and NH3-N removal (96.2%) was achieved at 150 µmol m−2 s−1 light intensity, 25 °C and N/P ratio = 1.5/1. The highest biomass concentration and carbohydrate content was 6.10 g L−1 and 50.46%, respectively, when N/P ratio = 5/1. The resulting carbohydrate-rich microalgal biomass was pretreated and used as a feedstock for butanol fermentation. With the initial sugar concentration of 48.7 g L−1 glucose and 3.4 g L−1 xylose in the pretreated biomass, the butanol concentration, yield, and productivity were 12.0 g L−1, 0.60 mol mol−1 sugar, and 0.89 g L−1 h−1, respectively, indicating the high potential of using Neochloris aquatica CL-M1 for butanol fermentation.

Temperature as an important ecological factor affects biofilm development and microbial metabolic activity. Here, the performances and microbial communities of microbial fuel cells (MFCs) at different temperature were analyzed. As the temperature decreased, the power output of MFCs declined. A maximum power density of 894.3±48.6mW/m2 was obtained in MFCs operating at 30°C, which was 18.5% and 64.5% higher than that in MFCs at 20°C and 10°C, respectively. Illumina sequencing of 16S rRNA gene amplicons showed that a distinct difference in microbial community structure of the anode biofilms occurred. This resulted in different power outputs of MFCs. Species diversity analyses indicated that species evenness of the anode biofilms shifted beyond species richness at different temperatures. The predominant populations of the anode biofilm shifted from Geobacter and Azonexus (30°C) to Pelobacter (20°C) or Acidovorax, Zoogloea and Simplicispira, (10°C). These results indicate that temperature plays an important role in shaping microbial communities of the anode biofilms in MFCs through changes in species evenness.

For deeply understanding the H 2 production promotion mechanism by adding Mg 2+ and Fe 2+ in Ethanoligenens harbinense fermentation process, the effects on cell growth, liquid byproducts production and H 2 yield at growth level were investigated, meanwhile the expressions of [FeFe]-hydrogenase, acetate kinase, alcohol dehydrogenase and lactate dehydrogenase with quantitative reverse transcription PCR at transcript level were monitored. The experimental results indicated that Mg 2+ makes more contributions on cell growth, but with Mg 2+ concentration increasing the expressions of functional genes were obviously suppressed. Fe 2+ has slightly positive effects on increasing cell growth and functional genes expression, which is inferred the reason of H 2 production enhancement. A maximum hydrogen yield of 2.14 mol-H 2 /mol-glucose was obtained in optimal medium supplemented with 600 mg/l MgCl 2 ·6H 2 O and 100 mg/l FeSO 4 ·7H 2 O. The realization of hydrogen production enhancement of E. harbinense by adding promoting factors was not only realized through increasing cell biomass growth and hydrogenase activity, but also some promotion effects on functional enzyme genes expressions.

Background Simultaneous wastewater treatment and lipid production by oleaginous microalgae show great potential to alleviate energy shortage and environmental pollution, because they exhibit tremendous advantages over traditional activated sludge. Currently, most research on wastewater treatment by microalgal are carried out at optimized temperature conditions (25–35 °C), but no information about simultaneous wastewater treatment and lipid production by microalgae at low temperatures has been reported. Microalgal growth and metabolism will be inhibited at low temperature conditions, and satisfactory wastewater treatment performance will be not obtained. Therefore, it is critical to domesticate and screen superior microalgal strains with low temperature adaptability, which is of great importance for wastewater treatment and biodiesel production. Results In this work, simultaneous wastewater treatment and lipid production were achieved by a microalgal mutant Scenedesmus sp. Z-4 at the low temperature conditions (4, 10, and 15 °C). The results showed that algal growth was inhibited at 4, 10, and 15 °C compared to that at the optimal temperature of 25 °C. However, decreased temperature had no significant effect on the total cellular lipid content of algae. Importantly, lipid productivity at 10 °C was compromised by more net energy output relevant to biodiesel production, which demonstrated that the low temperature of 10 °C was favorable to wastewater treatment and energy recovery by Scenedesmus sp. Z-4. When molasses wastewater with optimal COD concentration of 8000 mg L−1, initial inoculation ratio of 15%, and C/N ratio of 15 was used to cultivate microalgae, the maximum removal rate of COD, TN, and TP at 10 °C reached 87.2, 90.5, and 88.6%, respectively. In addition, lipid content of 28.9% and lipid productivity of 94.4 mg L−1 day−1 were obtained. Conclusions Scenedesmus sp. Z-4 had good adaptability to low temperature conditions, and showed great potential to realize simultaneous wastewater treatment and lipid production at low temperatures. The proposed approach in the study was simple compared to other wastewater treatment methods, and this potential novel process was still efficient to remove COD, N, and P at low temperatures. Thus, it had a vital significance for the wastewater treatment in low temperature regions.

The microbial electrochemical cell (MEC) is a promising waste treatment technology to accomplish simultaneous alternative energy production and degradation of organic matters. Potato pulp waste (PPW) from a potato processing plant contains a large amount of carbohydrates that need be degradated before discharge into the environment. Here, we describe electricity generation in single-chamber microbial fuel cells (MFCs) using PPW. Different organic loadings of PPW influenced obviously the power output of MFCs. The maximum power density of 32.1 ± 0.5 W m−3 was obtained in a MFC fed with 10 g L−1 PPW. Microbial community analysis based on high-throughput sequencing of 16S rRNA gene indicated that the predominant populations were obviously different in the MFCs. The syntrophic interactions between polysaccharide-degrading bacteria and exoelectrogens in the anode biofilms drove the cascade utilization of potato pulp waste in MFCs.

Low H2 yield from biomass impedes the industrial application of biohydrogen production. To improve H2 yield, the effect of Ginkgo biloba leaf (GL) on H2 production was investigated in this study. In batch fermentation with sugarcane molasses (SM), the addition of GL improved H2 yield by 28.03%. SM medium was optimized with response surface methodology (RSM) to determine the best concentrations of GL, SM, and an inexpensive nitrogen source—corn steep liquor (CSL). A maximum yield of 1.58 mol-H2/mol-hexose from SM was obtained when GL, CSL and SM hexose were 2.31 g/L, 2.28 g/L and 10 g/L, respectively. As observed with metabolic flux analysis, GL enhanced H2 conversion from SM via altering the metabolic flux distribution of E. harbinense from ethanol pathway towards acetate pathway. This study demonstrated the promotion effect of GL on H2 production from SM, raising a novel method for enhanced biohydrogen production in large scales.

In this study, the growth and lipid accumulation of Scenedesmus sp. using different nanoparticles and light sources were investigated. Xenon lamp can produce a broad illumination spectrum, and exhibited better performance than light-emitting diode. SiC and g-C3N4 nanoparticles improved the biomass and lipid accumulation, whereas TiO2 and TiC nanoparticles had inhibitory influence on microalgae. Lipid production can be improved by oxidative stress produced by combination of nanoparticles and xenon lamp irradiation. At the optimal SiC nanoparticles concentration of 150 mg L−1 and photoperiod of 6:18 h, the maximum biomass concentration and total lipid content reached 3.18 g L−1 and 40.26%, respectively. The addition of SiC nanoparticles could promote the substrate utilization rate and induce stress condition, thereby enhancing the activity of acetyl-CoA carboxylase and lipid biosynthesis. This research shows that SiC nanoparticles addition combined with xenon lamp illumination is a promising strategy to promote microalgal growth and lipid accumulation.