Sludge bio-drying: Effective to reduce both antibiotic resistance genes and mobile genetic elements

Abstract

a b s t r a c tSewage sludge is considered as one of major contributors to the increased environmental burden of ARGs. Sludge bio-drying was increasingly adopted due to its faster sludge reduction compared with composting. The fate of ARGs during full-scale sludge bio-drying was investigated to determine whether it could effectively reduce ARGs, and the contributions of bacterial community, horizontal gene transfer (HGT) through mobile genetic elements (MGEs) and co-selection from heavy metals to ARGs profiles were discussed in detail. Two piles with different aeration strategies (Pile I, the improved and Pile II, the control) were operated to elucidate effects of aeration strategy on ARGs profiles. Results showed that sludge bio-drying could effectively reduce both most of targeted ARGs (0.4e3.1 logs) and MGEs (0.8e3.3 logs) by the improved aeration strategy, which also enhanced both the sludge bio-drying performance and ARGs reduction. The enrichment of ARGs including ermF, tetX and sulII could be well explained by the evolution of bioavailable heavy metals, not HGT through MGEs, and their potential host bacteria mainly existed in Bacteroidetes. Although changes of bacterial community contributed the most to ARGs profiles, HGT through MGEs should be paid more attention especially in the thermophilic stage of sludge bio-drying.

Horizontal gene transfer and shifts in linked bacterial community composition are associated with maintenance of antibiotic resistance genes during food waste composting

“…In particular, the abundances of tetL, sul2, strA, ermB, ISCR1 and intI1 were enriched by 9.5, 10.7, 10.7, 377.2, 69.4, and 48.0 times, respectively (Figure 1c). This result is in line with previous studies showing that abundances of tetL, sul2, ermB can be found in reasonably high abundances after composting (Qian et al, 2016;Zhang et al, 2016).…”

“…Therefore, we decided to study the abundance of these ARGs during FW composting by choosing ten tetracycline resistance genes (tetA, tetB, tetC, tetG, tetL, tetM, tetQ, tetO, tetW, and tetX), seven macrolide resistance genes (ermB, ermF, ermM, ermT, ermX, mefA, and ereA), seven aminoglycoside resistance genes (aacA4, aadA, aadB, aadE, aphA1, strA, and strB), and three sulfonamide resistance genes (sul1, sul2, and sul3) totaling 27 different ARGs. To investigate potential changes in the abundance of mobile genetic elements (MGEs), we measured abundances of two integrase genes (intI1, intI2), two plasmid genes (ISCR1, IncQ) and one transposon (Tn916/1545, abbreviated as Tn916) gene that have often been connected with the movement of ARGs in the environment (Ma et al, 2017;Zhang et al, 2016). The bacterial abundance was measured as 16S rRNA gene copy numbers using SYBR-Green qPCR.…”

“…However, it is unclear how the specific physicochemical properties of FW affect the dynamics of ARGs during composting. Composting is a complex fermentation process that induces dynamic changes in biotic components such as the microbial community structure and abiotic factors including physicochemical properties of compost (Su et al, 2015;Zhang et al, 2016). These could potentially drive the abundance and composition of ARGs and MGEs directly or have indirect effects on their bacterial hosts.…”

Effect of pyrolysis on the removal of antibiotic resistance genes and class I integrons from municipal wastewater biosolids

“…Sludge bio-drying of municipal biosolids effectively reduced levels of the 16S rRNA, intI1, sul1, and erm(B) genes by 0.3 to 0.99-log. 67 Similarly, composting of sewage sludge (20 -60°C) substantially reduced the erm(B) genes levels by 1.55log, but failed to reduce levels of the sul1 and intI1 genes. 68 Previous studies have suggested that more rigorous technologies such as biosolids incineration are zero-risk solutions for the reduction of ARGs, although there are trade-offs with air quality and the loss of value-added soil amendment products.…”

Antibiotic-Resistance Genes in Waste Water

“…Recent work has also demonstrated that HGT is promoted in subinhibitory concentrations of antibiotics [43] and that positive selection might even inhibit HGT by eliminating possible recipients in the environment [44]. However, the analysis of ARG transfer in WWTPs is seriously hindered by the lack of suitable methods for high-throughput assessment of ARG transfer under real WWTP conditions, so it is not surprising that there is a knowledge gap in our understanding of the transfer of ARGs in WWTPs [45,46].…”