Effects of earthworms on the fate of tetracycline and fluoroquinolone resistance genes of sewage sludge during vermicomposting

Abstract

Diverse antibiotic resistance genes (ARGs) present in sewage sludge are difficult to be eliminated using conventional sludge treatment processes. To date, little remains known on the fate of the ARGs during vermicomposting of sludge. This study aimed to investigate the effect of earthworms on the fate of tetracycline and fluoroquinolone resistance genes, and integrons during vermicomposting of sewage sludge through contrasting two systems of sludge stabilization with and without earthworms. Compared to the control without earthworms, vermicomposting significantly (p < 0.05) decreased the abundances of tetracycline and fluoroquinolone resistance genes and int1, with complete removal for parC. Variations in ARGs were associated with environmental factors, horizontal gene transfer, bacterial community composition, and earthworms during vermicomposting. In addition, earthworms strongly affected the possible host bacteria encoding ARGs and Int1, abating the pathogenic bacteria in vermicomposting product. These results imply that vermicomposting could effectively reduce tetracycline and fluoroquinolone resistance genes in the sludge.

Quality of Vermicompost and Microbial Community Diversity Affected by the Contrasting Temperature during Vermicomposting of Dewatered Sludge

“…For each reactor, 100 young and active earthworms with an average weight of 0.5 g were inoculated into each vermireactor filled with 4 kg fresh sludge. This density of earthworms was based on the previous studies [6,12]. To maintain the moisture of 70-80%, each reactor was covered with a plastic film with some small holes.…”

“…The fresh sludge was fumigated with chloroform before being used to measure the microbial biomass carbon (MBC) via the spectrophotometric method following Fu et al [12]. Dehydrogenase activity (DHA) was also determined to evaluate microbial activity using the triphenyl tetrazolium chloride (TTC) method [6].…”

“…V3-V4 regions of the bacterial 16S rRNA gene were amplified using the universal primers of 304f-806r [6]. The Polymerase chain reaction (PCR) was carried out in a 25 µl mixture comprised of 1 µL DNA template, 2.5 µL of each forward and reverse primer (0.5 µM each), 25 µL polymerase (Phusion ® High-Fidelity PCR Master Mix, New England Biolabs, Beijing, China), and 19 µL DNA-free water.…”

“…Compared with incineration and landfills, the sludge fertilizer product combined with the agricultural use is deemed as a potential method of recycling to resolve the sludge problem in China [1] based on the control standards for sludge products for agricultural use (GB 4284-2018). Vermicomposting is a biochemical method for converting sludge into high-value organic microbial fertilizer by the joint action of earthworms and microorganisms [4][5][6][7]. As a green technology, plenty of vermicomposting factories for treating sludge have been recently established in China allowing them to profit highly from vermicompost and vermiculture in the process.…”

“…For instance, Eisenia fetida as a ubiquitous epigenetic species capable of vermicomposting exhibited wide tolerance to a broad temperature range (15-25 • C) for their growth [11]. Previous studies also indicate high variability in the temperature used for vermicomposting with most using room temperature, also suggesting a wide range of temperature useful for treating sludge [6,12,13]. Only a few publications clearly reported that 20 • C was the optimal temperature condition for treating activated sludge [14].…”