Biochar and Hyperthermophiles as Additives Accelerate the Removal of Antibiotic Resistance Genes and Mobile Genetic Elements during Composting

Abstract

Sewage treatment plants are known as repositories of antibiotic resistance genes (ARGs). Adding biochar and inoculating with exogenous microbial agents are common ways to improve the quality of compost. However, little is known about the effects of these exogenous additives on the fate of ARGs during composting and the related mechanisms. In this study, municipal sludge was taken as the research object to study the ARG-removal effects of four composting methods: ordinary compost (CT), compost with hyperthermophiles (HT), compost with hyperthermophiles and 2.0% biochar (HT2C) and compost with hyperthermophiles and 5.0% biochar (HT5C). Real-time quantitative PCR (qPCR) and 16S rRNA high-throughput sequencing were conducted to analyze the ARGs, MGEs and bacterial community. After composting, the abundance of ARGs in CT was reduced by 72.7%, while HT, HT2C and HT5C were reduced by 80.7%, 84.3% and 84.8%, respectively. Treatments with different proportions of biochar added (HT2C, HT5C) had no significant effect on the abundance of ARGs. Network analysis showed that Firmicutes and Nitrospirae were positively associated with most ARGs and may be potential hosts for them. In addition, redundancy analysis further showed that the class 1 integrase gene (intI1), pH and organic carbon had a greater effect on ARGs. Our findings suggested that the combination of hyperthermophiles and biochar during the composting process was an effective way to control ARGs and mobile genetic elements (MGEs), thus inhibiting the spread and diffusion of ARGs in the environment and improving the efficiency of treating human and animal diseases.

Metagenomic Insights Into the Changes of Antibiotic Resistance and Pathogenicity Factor Pools Upon Thermophilic Composting of Human Excreta

“…In a recent study on municipal sludge three treatments apart from the control without additives were tested: addition of hyperthermophiles, hyperthermophiles with 2% biochar, hyperthermophiles with 5% biochar. Biochar significantly increased ARG removal rates, but no significant differences between the different biochar contents were found ( Fu et al, 2021 ). Further research would be needed to understand the mechanisms behind different biochar or compost types and biochar contents on ARG removal.…”

Organic amendment treatments for antimicrobial resistance and mobile element genes risk reduction in soil-crop systems

“…A previous study 39 evaluated the effects of applying rice straw biochar and mushroom biochar during chicken manure composting on ARG removal (including sul1 , sul2 , tetA , and tetX genes). The removal rate of sul1 , sul2 , tetA and intl1 genes by adding biochar 5% was significantly higher than the control treatment during composting 40 . At the end of the composting process, the addition of biochar led to a decrease of the relative abundance of Bacteroidetes and Firmicutes 40 .…”

Biochar can mitigate co-selection and control antibiotic resistant genes (ARGs) in compost and soil

“…(2017) Tree leaves Sludge, back-mix peanut shell; 3:1:1 w/w/w 2 & 5 550 3 66 Biochar addition had a 4% increase in ARGs elimination when compared to hyperthermophiles (80.7%). There was no significant different between the two biochar doses (2% and 5%) Fu et al. (2021) Corn cob & rice husk Sludge & Eisenia fetida 1.25 & 5 NA NA 60 ermF & tetX genes were decreased by corncob biochar.…”

“…A range of 2–10% application dose have been reported to be effective in the reduction of HMs bioavailability and ARGs abundance. An addition of 5% dose of biochar had no better effect over 2% ( Fu et al., 2021 ); 10% was proposed as the best over 5% and 20% ( Li et al., 2017 ); 7.5% was better than 2.5%, 5%, and 10% ( Awasthi et al., 2021 ); and 6% was proposed as the best over 12% and 24% ( Wang et al., 2018 ). There is a concern that biochar at 12% dose may increase the distribution and transfer of ARGs ( Wang et al., 2018 ).…”

“…Rice straw biochar failed to reduce ARGs in chicken manure composting when compared to mushroom biochar and this was attributed to the presence of Actinobacteria and Firmicutes (which could distribute ARGs in the compost) and not the property of the biochar ( Cui et al., 2016a ). In the presence of hyperthermophiles, biochar addition enhanced ARGs elimination during municipal sludge composting, though this was not significant ( Fu et al., 2021 ). Application of biochar resulted only in a 4% increase in ARGs removal when compared to hyperthermophiles (80.7%).…”