Efficient nitrogen removal via simultaneous ammonium assimilation and heterotrophic denitrification of Paracoccus denitrificans R-1.

Although diverse microorganisms can remove ammonium and nitrate simultaneously, their metabolic mechanisms are not well understood. Paracoccus denitrificans R-1 showed the maximal NH4 + removal rate 9.94 mg L-1·h-1 and 2.91 mg L-1·h-1 under aerobic and anaerobic conditions, respectively. Analysis of the nitrogen balance calculation and isotope tracing experiment indicated that NH4 + was consumed through assimilation. The maximal NO3 - removal rate of strain R-1 was 18.05 and 19.76 mg L-1·h-1 under aerobic and anaerobic conditions, respectively. The stoichiometric consumption ratio of acetate to nitrate was 0.902 and NO3 - was reduced to N2 for strain R-1 through 15NO3 - isotopic tracing experiment, which indicated a respiratory process coupled with the oxidation of electron donors. Genomic analysis showed that strain R-1 contained genes for ammonium assimilation and denitrification, which effectively promoted each other. These findings provide insights into microbial nitrogen transformation and facilitate the simultaneous removal of NH4 + and NO3 - in a single reactor.

Integration of Multi-Omics, Histological, and Biochemical Analysis Reveals the Toxic Responses of Nile Tilapia Liver to Chronic Microcystin-LR Exposure.

Microcystin-LR (MC-LR) is a cyanobacterial metabolite produced during cyanobacterial blooms and is toxic to aquatic animals, and the liver is the main targeted organ of MC-LR. To comprehensively understand the toxicity mechanism of chronic exposure to environmental levels of MC-LR on the liver of fish, juvenile Nile tilapia were exposed to 0 µg/L (control), 1 µg/L (M1), 3 µg/L (M3), 10 µg/L (M10), and 30 µg/L (M30) MC-LR for 60 days. Then, the liver hepatotoxicity induced by MC-LR exposure was systematically evaluated via histological and biochemical determinations, and the underlying mechanisms were explored through combining analysis of biochemical parameters, multi-omics (transcriptome and metabolome), and gene expression. The results exhibited that chronic MC-LR exposure caused slight liver minor structural damage and lipid accumulation in the M10 group, while resulting in serious histological damage and lipid accumulation in the M30 group, indicating obvious hepatotoxicity, which was confirmed by increased toxicity indexes (i.e., AST, ALT, and AKP). Transcriptomic and metabolomic analysis revealed that chronic MC-LR exposure induced extensive changes in gene expression and metabolites in six typical pathways, including oxidative stress, apoptosis, autophagy, amino acid metabolism, primary bile acid biosynthesis, and lipid metabolism. Taken together, chronic MC-LR exposure induced oxidative stress, apoptosis, and autophagy, inhibited primary bile acid biosynthesis, and caused fatty deposition in the liver of Nile tilapia.

Elucidating the regulatory role of long non-coding RNAs in drought stress response during seed germination in leaf mustard.

Leaf mustard (Brassica juncea L. Czern & Coss), an important vegetable crop, experiences pronounced adversity due to seasonal drought stress, particularly at the seed germination stage. Although there is partial comprehension of drought-responsive genes, the role of long non-coding RNAs (lncRNAs) in adjusting mustard's drought stress response is largely unexplored. In this study, we showed that the drought-tolerant cultivar 'Weiliang' manifested a markedly lower base water potential (-1.073 MPa vs -0.437 MPa) and higher germination percentage (41.2% vs 0%) than the drought-susceptible cultivar 'Shuidong' under drought conditions. High throughput RNA sequencing techniques revealed a significant repertoire of lncRNAs from both cultivars during germination under drought stress, resulting in the identification of 2,087 differentially expressed lncRNAs (DELs) and their correspondingly linked 12,433 target genes. It was noted that 84 genes targeted by DEL exhibited enrichment in the photosynthesis pathway. Gene network construction showed that MSTRG.150397, a regulatory lncRNA, was inferred to potentially modulate key photosynthetic genes (Psb27, PetC, PetH, and PsbW), whilst MSTRG.107159 was indicated as an inhibitory regulator of six drought-responsive PIP genes. Further, weighted gene co-expression network analysis (WGCNA) corroborated the involvement of light intensity and stress response genes targeted by the identified DELs. The precision and regulatory impact of lncRNA were verified through qPCR. This study extends our knowledge of the regulatory mechanisms governing drought stress responses in mustard, which will help strategies to augment drought tolerance in this crop.

Transcriptome profile analysis of Indian mustard (Brassica juncea L.) during seed germination reveals the drought stress-induced genes associated with energy, hormone, and phenylpropanoid pathways.

Indian mustard (Brassica juncea L. Czern and Coss) is an important oil and vegetable crop frequently affected by seasonal drought stress during seed germination, which retards plant growth and causes yield loss considerably. However, the gene networks regulating responses to drought stress in leafy Indian mustard remain elusive. Here, we elucidated the underlying gene networks and pathways of drought response in leafy Indian mustard using next-generation transcriptomic techniques. Phenotypic analysis showed that the drought-tolerant leafy Indian mustard cv. 'WeiLiang' (WL) had a higher germination rate, antioxidant capacity, and better growth performance than the drought-sensitive cv. 'ShuiDong' (SD). Transcriptome analysis identified differentially expressed genes (DEGs) in both cultivars under drought stress during four germination time points (i.e., 0, 12, 24, and 36 h); most of which were classified as drought-responsive, seed germination, and dormancy-related genes. In the Kyoto Encyclopedia of Genes and Genome (KEGG) analyses, three main pathways (i.e., starch and sucrose metabolism, phenylpropanoid biosynthesis, and plant hormone signal transduction) were unveiled involved in response to drought stress during seed germination. Furthermore, Weighted Gene Co-expression Network Analysis (WGCNA) identified several hub genes (novel.12726, novel.1856, BjuB027900, BjuA003402, BjuA021578, BjuA005565, BjuB006596, novel.12977, and BjuA033308) associated with seed germination and drought stress in leafy Indian mustard. Taken together, these findings deepen our understanding of the gene networks for drought responses during seed germination in leafy Indian mustard and provide potential target genes for the genetic improvement of drought tolerance in this crop.

[Action modes of chlorine dioxide--a review].

Chlorine dioxide (ClO2) is a highly effective disinfectant for food and potable water treatment. Till now, the action mode of ClO2 is still unclear. ClO2, can denature proteins by oxidizing tyrosine, tryptophan, and cysteine. We reviewed the pathways by which ClO02 reacts with important bio-molecules, as well as the primary target sites at individual cellular level of ClO2-induced biocidal effects.

Existence and distribution of novel phylotypes of Nitrospira in water columnsof the South China Sea.

In the biological nitrogen cycle, nitrite oxidation is performed by nitrite oxidation bacteria, of which Nitrospira is widespread and diverse. Communities of Nitrospira were collected at 25-1500 m depths in the South China Sea. Phylogenetic diversity, community composition, and environmental factors were investigated using high-throughput sequencing targeting the nxrB gene and statistical analyses. The community composition of Nitrospira varied spatially and by depth. Among the 24 OTUs with relatively high abundance, 70% were unclassified and not affiliated with the known Nitrospira genus, suggesting a previously unrecognized high diversity of marine Nitrospira. Five known Nitrospira genera were detected, of which the common marine Nitrospira marina was not the dominant species, whereas Candidatus Nitrospira lenta and Candidatus Nitrospira defluvii dominated in shallow habitats. Comammox Candidatus Nitrospira nitrosa was discovered in the marine ecosystem. The niche differentiation of versatile Nitrospira species was mainly shaped by nitrate, temperature, and DO.

[Bactericidal effects of chlorine dioxide by respiratory inhibition].

OBJECTIVE: Chlorine dioxide (ClO2) is a highly effective disinfectant for food and potable water treatment. However, knowledge on its action mechanism remains unexplored. The present study aims to determine the role of respiratory inhibition in the bactericidal effects of ClO2. METHODS: Transmission electron microscopy was used to observe the ultra structural alteration of the mitochondrion. Fluorescence-based flow cytometry analysis was employed to determine the disruption of mitochondrion membrane potential. Respiratory inhibition was detected by measuring the oxygen consumption. The results obtained were compared with those of plate counting. RESULTS: No visible physiological alteration in the shapes and structures of the mitochondria was found. The rate of collapse in mitochondrial membrane potential increased with the death rate, but the respiratory inhibition rates were always significantly lower than the death rates. The death rates detected by the aerobic and anaerobic methods did not differ significantly. CONCLUSION: ClO2-induced damages to the mitochondria were positive correlated with the death rates, but respiratory inhibition was not the primary target site for cell killing.

Application of Chlorine Dioxide in Cell Surface Modification to Enhance Its Mechanical Stability and Metal Ion Adsorption.

There has been a trend toward the use of microorganisms as the biomaterial for removing dyes and metals from wastewater. However, native microorganism cells have low mechanical stability, which limit their further application in industries. In this study, chlorine dioxide (ClO2), a high-efficiency, low-toxicity, and environmentally benign disinfectant, was used for microorganism surface modification to enhance the mechanical stability and metal ion adsorption of the cell. ClO2 can either modify cell walls to improve their metal adsorption capacity or modify cell membranes to improve their mechanical stability. Fourier-transform infrared spectroscopy analysis indicated that several cell surface groups were involved in the cell wall modification of Bacillus sp. Microscopic observation indicated that ClO2 treatment could deter cell membranes from forming vesicles in sodium hydroxide (NaOH) aqueous solution, and freeze-etching showed that ClO2 treatment could alter the erythrocyte membrane proteins which might also contribute to improving the cell stability. The experimental results on Bacillus sp., Pseudomonas aeruginosa, and Mucor rouxii show that ClO2 treatment may increase, or at least not reduce, the ability of microbial cells to adsorb heavy metals, but it can significantly improve the resistance of these cells to NaOH cleavage. It seems ClO2 is a promising auxiliary for biosorption of heavy-metal ions.