Mechanism for combined application of biochar and Bacillus cereus to reduce antibiotic resistance genes in copper contaminated soil and lettuce.

The remediation of agricultural soil contaminated by antibiotic resistance genes (ARGs) is of great significance for protecting food safety and human health. Reducing the availability of copper in soil may control coresistance to ARGs. However, the feasibility of applying nano-biochar and Bacillus cereus to mitigate the spread of ARGs in Cu contaminated soil remains unclear. Therefore, this study investigated the use of biochar with different particle sizes (2 % apple branch biochar and 0.5 % nano-biochar) and 3 g m-2B. cereus in a 60-day pot experiment with growing lettuce. The effects of single and combined application on the abundances of ARGs in Cu-contaminated soil (Cu = 200 mg kg-1) were compared, and the related mechanisms were explored. Studies have shown that the addition of biochar alone is detrimental to mitigating ARGs in soil-lettuce systems. The combined application of 3 g m-2B. cereus and 0.5 % nano-biochar effectively inhibited the proliferation of ARGs in Cu-contaminated soil, and 3 g m-2B. cereus effectively inhibited the proliferation of ARGs in lettuce. Partial least squares-path modeling and network analysis showed that bacterial communities and mobile genetic elements were the key factors that affected the abundances of ARGs in rhizosphere soil, and Cu resistance genes and bioavailable copper (acid extractable state Cu (F1) + reducing state Cu (F2)) had less direct impacts. The bacterial community was the key factor that affected the abundances of ARGs in lettuce. Rhodobacter (Proteobacteria), Corynebacterium (Actinobacteria), and Methylobacterium (Proteobacteria) may have been hosts of ARGs in lettuce plants. B. cereus and nano-biochar affected the abundances of ARGs by improving the soil properties and reducing the soil bioavailability of Cu, as well as directly or indirectly changing the bacterial community composition in soil and lettuce, thereby impeding the transport of ARGs to aboveground plant parts.

Integrated microbiological and metabolomics analyses to understand the mechanism that allows modified biochar to affect the alkalinity of saline soil and winter wheat growth.

In order to understand the mechanism that allows modified biochar (BC) to enhance the salt tolerance and growth of crops in saline-alkali soil, we tested the effects of ordinary BC, nanoparticle-size BC, acidified BC (HBC), and acidified nanoparticle-size BC on winter wheat growth and the soil properties by combining microbiological and metabolomics analyses. The results showed that compared with the control with no BC, the plant height increased by 17.33 % under HBC and the proportion of large soil aggregates increased by 1.25-2.83 times. HBC increased the relative abundances of some dominant genera of bacteria (e.g., Streptococcus) and fungi (e.g., Mycothermus), as well as functions such as bacterial metabolic genetic information processing and cellular processes, and reduced the abundance of pathotrophic fungi. Metabolomics analysis showed that HBC upregulated various metabolites (including amino acids and their derivatives, lipids, flavonoids, and organic acids) and five main metabolic pathways. Among the KEGG pathways, the pyrimidine metabolism pathway was significantly upregulated, as well as crop leaf metabolism, ß-alanine metabolism, and valine, leucine, and isoleucine metabolism, and the antioxidant levels and resistance to salt-alkali stress were enhanced in winter wheat leaves. Partial least squares-path modeling suggested that HBC affected the growth of winter wheat by significantly changing the soil physicochemical properties and microbial structure (path coefficients of 0.566 and 0.512, respectively).