The Impact of Chicken Manure Biochar on Antibiotic Resistance Genes in Chicken Manure Composting

One way to increase yields in agriculture using organic alternative methods is the introduction of manure-based composts into the soil. However, the use of such composts carries a risk of soil contamination with antibiotic resistance genes (ARG) from the gut and manure of the livestock. The contamination of the composts with heavy metals or antibiotics can increase this risk, while the addition of porous materials, such as biochar, to the composts has the potential to decrease it. This study is devoted to revealing the fate of ARGs in bedding chicken manure composted with the addition of oxytetracycline (OTC), heavy metals, and chicken manure biochar. It was revealed that the additives did not affect the physicochemical parameters of the compost. The bacterial communities in different composting mixtures had similar structures and dynamics. It was revealed that the shifts of the bacterial compositions of the composting mixtures were mainly determined by the duration of the process. However, some minor differences in the OTU (operational taxonomic unit) levels were observed between the variants. The addition of biochar and metals led to 26.7% and 34.5% decreases, respectively, in the number of tet(A) gene copies, while the addition of oxytetracycline led to a 43.7% increase. The number of copies of the int1 gene increased by 45.9% after the addition of oxytetracycline. The correlation between the abundance levels of different bacterial OTU and ARG contents was estimated, and biochar's impact on those OTUs was analyzed. It was assumed that some OTUs might be carriers of ARGs (such as Natronobacillus, Luteimonas, and Trichococcus), and their abundance in the presence of the biochar decreased due to competitive exclusion by noncarriers (such as Corynebacterium, Clostridia, and Halorhodospira). The use of biochar in composting can be considered a way to reduce the contamination of the final composts with ARGs.