Structural and Kinetic Characterization of Hyperthermophilic NADH-Dependent Persulfide Reductase from Archaeoglobus fulgidusRead the full article
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Analysis of a Methanogen and an Actinobacterium Dominating the Thermophilic Microbial Community of an Electromethanogenic Biocathode
Electromethanogenesis refers to the bioelectrochemical synthesis of methane from CO2 by biocathodes. In an electromethanogenic system using thermophilic microorganisms, metagenomic analysis along with quantitative real-time polymerase chain reaction and fluorescence in situ hybridization revealed that the biocathode microbiota was dominated by the methanogen Methanothermobacter sp. strain EMTCatA1 and the actinobacterium Coriobacteriaceae sp. strain EMTCatB1. RNA sequencing was used to compare the transcriptome profiles of each strain at the methane-producing biocathodes with those in an open circuit and with the methanogenesis inhibitor 2-bromoethanesulfonate (BrES). For the methanogen, genes related to hydrogenotrophic methanogenesis were highly expressed in a manner similar to those observed under H2-limited conditions. For the actinobacterium, the expression profiles of genes encoding multiheme c-type cytochromes and membrane-bound oxidoreductases suggested that the actinobacterium directly takes up electrons from the electrode. In both strains, various stress-related genes were commonly induced in the open-circuit biocathodes and biocathodes with BrES. This study provides a molecular inventory of the dominant species of an electromethanogenic biocathode with functional insights and therefore represents the first multiomics characterization of an electromethanogenic biocathode.
Performance Analysis and Microbial Community Evolution of In Situ Biological Biogas Upgrading with Increasing H2/CO2 Ratio
The effect of the amount of hydrogen supplied for the in situ biological biogas upgrading was investigated by monitoring the process and evolution of the microbial community. Two parallel reactors, operated at 37°C for 211 days, were continuously fed with sewage sludge at a constant organic loading rate of 1.5 gCOD∙(L∙d)-1 and hydrogen (H2). The molar ratio of H2/CO2 was progressively increased from 0.5 : 1 to 7 : 1 to convert carbon dioxide (CO2) into biomethane via hydrogenotrophic methanogenesis. Changes in the biogas composition become statistically different above the stoichiometric H2/CO2 ratio (4 : 1). At a H2/CO2 ratio of 7 : 1, the methane content in the biogas reached 90%, without adversely affecting degradation of the organic matter. The possibility of selecting, adapting, and enriching the original biomass with target-oriented microorganisms able to biologically convert CO2 into methane was verified: high throughput sequencing of 16S rRNA gene revealed that hydrogenotrophic methanogens, belonging to Methanolinea and Methanobacterium genera, were dominant. Based on the outcomes of this study, further optimization and engineering of this process is feasible and needed as a means to boost energy recovery from sludge treatment.
Production of Poly(3-Hydroxybutyrate) by Haloarcula, Halorubrum, and Natrinema Haloarchaeal Genera Using Starch as a Carbon Source
Microbial production of bioplastics, derived from poly(3-hydroxybutyrate) (PHB), have provided a promising alternative towards plastic pollution. Compared to other extremophiles, halophilic archaea are considered as cell factories for PHB production by using renewable, inexpensive carbon sources, thus decreasing the fermentation cost. This study is aimed at screening 33 halophilic archaea isolated from three enrichment cultures from Tunisian hypersaline lake, Chott El Jerid, using starch as the sole carbon source by Nile Red/Sudan Black staining and further confirmed by PCR amplification of phaC and phaE polymerase genes. 14 isolates have been recognized as positive candidates for PHA production and detected during both seasons. The identification of these strains through 16S rRNA gene analyses showed their affiliation to Halorubrum, Natrinema, and Haloarcula genera. Among them, three PHB-producing strains, CEJ34-14, CEJ5-14, and CEJ48-10, related to Halorubrum chaoviator, Natrinema pallidum, and Haloarcula tradensis were found to be the best ones reaching values of 9.25, 7.11, and 1.42% of cell dry weight (CDW), respectively. Our findings highlighted that Halorubrum, Natrinema, and Haloarcula genera were promising candidates for PHB production using soluble starch as a carbon source under high salinity (250 g L-1 NaCl).
Flocculation Efficiency and Mechanism of Carbamazepine by Microbial Flocculant Extracted from Klebsiella pneumoniae J1
The microbial flocculant (MFX) extracted from Klebsiella pneumoniae J1 was used to remove carbamazepine in prepared wastewater and domestic sewage. The influence factors and flocculation mechanism were studied. The optimal carbamazepine removal conditions for MFX were pH of 7-8, 7 mL of flocculant, 0.1 mL of coagulant, and 35°C, and the removal rate reached 81.75%. MFX was efficient in the removal of carbamazepine in both domestic sewage (75.03%) and secondary sedimentation tank effluent (69.76%). The pseudo-first-order kinetic equation fitted the adsorption process better than the pseudo-second-order kinetic equation, which suggested that the adsorption was not pure chemical adsorption. The analysis of floc size suggested that the repulsive force between carbamazepine and MFX was weakened under alkalescent conditions, which can help the growth and coherence of flocs and increase the carbamazepine removal efficiency. Enough dosage of MFX can generate larger flocs, but excessive dosage of MFX will decrease the carbamazepine removal rate because of increase in electrostatic repulsion. The analysis of 3D-EEM and FTIR suggested that hydroxyl, amino, and carboxyl in MFX played an important role in the removal of carbamazepine. As an eco-friendly and highly efficient microbial flocculant, MFX has potential for practical applications in carbamazepine removal.
Thermophilic Solid-State Anaerobic Digestion of Corn Straw, Cattle Manure, and Vegetable Waste: Effect of Temperature, Total Solid Content, and C/N Ratio
Thermophilic solid-state anaerobic digestion (SS-AD) of agricultural wastes, i.e., corn straw, cattle manure, and vegetable waste, was carried out in this study. The effects of temperature (40-60°C), initial solid content (ISC, 17.5-32.5%), and C/N ratio (15-32 : 1) on biogas production were evaluated using a Box-Behnken experimental design (BBD) combined with response surface methodology (RSM). The results showed that optimization of process parameters is important to promote the SS-AD performance. All the factors, including interactive terms (except the ISC), were significant in the quadratic model for biogas production with SS-AD. Among the three operation parameters, the C/N ratio had the largest effect on biogas production, followed by temperature, and a maximum biogas yield of 241.4 mL gVS-1 could be achieved at 47.3°C, , and . After 20 d of SS-AD, the microbial community structure under different conditions was characterized by high-throughput sequencing, showing that Firmicutes, Bacteroidetes, Chloroflexi, Synergistetes, and Proteobacteria dominated the bacterial community, and that Firmicutes had a competitive advantage over Bacteroidetes at elevated temperatures. The biogas production values and relative abundance of OPB54 and Bacteroidia after 20 d of SS-AD can be fitted well using a quadratic model, implying that OPB54 and Bacteroidia play important roles in the methanogenic metabolism for agricultural waste thermophilic SS-AD.
Identification and Characterization of a Newly Isolated Chitinase-Producing Strain Bacillus licheniformis SSCL-10 for Chitin Degradation
Chitinases or chitinolytic enzymes have different applications in the field of medicine, agriculture, and industry. The present study is aimed at developing an effective hyperchitinase-producing mutant strain of novel Bacillus licheniformis. A simple and rapid methodology was used for screening potential chitinolytic microbiota by chemical mutagenesis with ethylmethane sulfonate and irradiation with UV. There were 16 mutant strains exhibiting chitinase activity. Out of the chitinase-producing strains, the strain with maximum chitinase activity was selected, the protein was partially purified by SDS-PAGE, and the strain was identified as Bacillus licheniformis (SSCL-10) with the highest specific activity of 3.4 U/mL. The induced mutation model has been successfully implemented in the mutant EMS-13 (20.2 U/mL) that produces 5-6-fold higher yield of chitinase, whereas the mutant UV-11 (13.3 U/mL) has 3-4-fold greater chitinase activity compared to the wild strain. The partially purified chitinase has a molecular weight of 66 kDa. The wild strain (SSCL-10) was identified as Bacillus licheniformis using 16S rRNA sequence analysis. This study explores the potential applications of hyperchitinase-producing bacteria in recycling and processing chitin wastes from crustaceans and shrimp, thereby adding value to the crustacean industry.