Herbicide Selection Promotes Antibiotic Resistance in Soil Microbiomes.

Herbicides are one of the most widely used chemicals in agriculture. While they are known to be harmful to nontarget organisms, the effects of herbicides on the composition and functioning of soil microbial communities remain unclear. Here we show that application of three widely used herbicides-glyphosate, glufosinate, and dicamba-increase the prevalence of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in soil microbiomes without clear changes in the abundance, diversity and composition of bacterial communities. Mechanistically, these results could be explained by a positive selection for more tolerant genotypes that acquired several mutations in previously well-characterized herbicide and ARGs. Moreover, herbicide exposure increased cell membrane permeability and conjugation frequency of multidrug resistance plasmids, promoting ARG movement between bacteria. A similar pattern was found in agricultural soils across 11 provinces in China, where herbicide application, and the levels of glyphosate residues in soils, were associated with increased ARG and MGE abundances relative to herbicide-free control sites. Together, our results show that herbicide application can enrich ARGs and MGEs by changing the genetic composition of soil microbiomes, potentially contributing to the global antimicrobial resistance problem in agricultural environments.

Linking microbial community structure with molecular composition of dissolved organic matter during an industrial-scale composting.

This study explored the interactions between dissolved organic matter (DOM) composition and microbial community structure during an industrial-scale composting by Fourier transform ion cyclotron resonance mass spectrometry and 16S rRNA sequencing analysis. The results revealed that DOM from matured compost contained primarily lignins/carboxylic-rich alicyclic molecules (73.6%), the higher double bond equivalent (5.97) and aromaticity index (0.18), indicating that the molecular composition of DOM had changed substantially. Drastic changes in microbial community structure were also observed along with the DOM transformation process of composting. Network analysis further indicated that Caldicoprobacter, Bacillus, and Dechloromonas were associated with the most DOM subcategories. Caldicoprobacter could degrade carbohydrates, Bacillus accelerated the humification by transforming N-containing compounds, and Dechloromonas could degrade polycyclic aromatic hydrocarbons distributed in low O/C. These findings are helpful for understanding the molecular mechanisms of DOM transformation and humification of sludge composting.

Phosphate recovery with granular acid-activated neutralized red mud: Fixed-bed column performance and breakthrough curve modelling.

Granular acid-activated neutralized red mud (AaN-RM) has been successfully prepared with good chemical stability and physical strength. However, its potential for industrial application remains unknown. Therefore, the performance of granular AaN-RM for phosphate recovery in a fixed-bed column was investigated. The results demonstrated that the phosphate adsorption performance of granular AaN-RM in a fixed-bed column was affected by various operational parameters, such as the bed depth, flow rate, initial solution pH and initial phosphate concentration. With the optimal empty-bed contact time (EBCT) of 24.27 min, the number of processed bed volumes and the phosphate adsorption capacity reached 496.95 and 84.80 mg/g, respectively. Then, the saturated fixed-bed column could be effectively regenerated with a 0.5 mol/L HCl solution. The desorption efficiency remained as high as 83.45% with a low weight loss of 3.57% in the fifth regeneration cycle. In addition, breakthrough curve modelling showed that a 5-9-1 feed-forward artificial neural network (ANN) could be effectively applied for the optimization of the fixed-bed adsorption system; the coefficient of determination (R2) and the root mean square error (RMSE) evaluated on the validation-testing data were 0.9987 and 0.0183, respectively. Therefore, granular AaN-RM fixed-bed adsorption exhibits promising potential for phosphate removal and recovery from polluted water.

Insights into compositional changes of dissolved organic matter during a full-scale vermicomposting of cow dung by combined spectroscopic and electrochemical techniques.

Various spectroscopic and electrochemical techniques combined was used to investigate the compositional changes of dissolved organic matter (DOM) and the difference in humification degree during full-scale cow dung vermicomposting. This study also investigated that whether the two techniques could be used as humification indices. The physicochemical characteristics of vermicompost were superior to those of the control, indicating that vermicomposting significantly accelerated the humification process, which was confirmed by spectroscopic and electrochemical analyses. Meanwhile, the changes of three components identified and electron transfer capacities in vermicomposting further revealed that vermicomposting resulted in significant compositional changes of DOM and higher humification degree. Partial least squares path modeling and redundancy analysis revealed that the two techniques could be used as humification indices for vermicomposting. These results of this study demonstrated that the combination of spectroscopy and electrochemistry was applicable to characterize the compositional changes of DOM and the humification degree of vermicomposting.