Higher Temperatures Do Not Always Achieve Better Antibiotic Resistance Gene Removal in Anaerobic Digestion of Swine Manure

Abstract

This study employed high-throughput quantitative PCR and 16S rRNA sequencing to evaluate the effect of temperature and residual antibiotics on the dynamics of antibiotic resistance genes (ARGs) and microbial communities during anaerobic digestion of swine manure. The abundances of total ARGs and 16S rRNA genes significantly decreased in all of four treatments (25°C, 37°C, and 37°C with 50 mg of wet weight antibiotics of body weight, and 55°C). The abundances of most ARG types were significantly correlated with those of the 16S rRNA gene and transposase gene (P < 0.01). However, the abundances of total ARGs at 55°C were much higher than those of other treatments. Meanwhile, the microbial communities at 55°C, where the Streptococcus pathogen remained at a relatively high abundance and cellulose degraders and hydrogen producers, such as Ethanoligenens and Coprococcus bacteria, increased, were markedly different from those of other treatments. Redundancy analysis indicates that temperature, pH, and the genus Streptococcus had the highest explanation for ARG variation among experimental factors, chemical properties, and representative genera, respectively. Network analysis further showed that the genus Streptococcus contributed greatly to the higher ARG abundance at 55°C. The moderate antibiotic residue only caused a slight and transitory inhibition for microbially diverse populations and promotion for ARG abundance, probably due to the degradation of antibiotics and microbial adaptability. Our results clarify the cooperativity of gene transfer-related items on ARG variation and intensively prove that higher temperature cannot always achieve better ARG removal in anaerobic digestion unless pathogens and gene transfer elements are more efficiently inhibited. IMPORTANCE Antibiotic resistance genes (ARGs) are frequently detected with high abundance in manure-applied soils. Anaerobic digestion is one of widely used processes for animal waste treatment. Thus, it is critical to understand the potential of anaerobic digestion to attenuate ARGs. Although some previous studies recommended thermophilic digestion for ARG removal, they did not get sufficient evidence to support this view. The antibiotics applied to animals are mostly excreted through feces and urine because of incomplete metabolism. It is indispensable to know whether residual antibiotics in manure will hinder ARG attenuation in anaerobic digesters. The significance of our research is in comprehensively understanding the evolution and mechanism of ARGs in anaerobic digestion of swine manure affected by temperature and residual antibiotics, which will allow the development of an ARG elimination strategy before their release into the environment.

Increased (Antibiotic-Resistant) Pathogen Indicator Organism Removal during (Hyper-)Thermophilic Anaerobic Digestion of Concentrated Black Water for Safe Nutrient Recovery

“…Both the World Economic Forum [24] and the World Health Organization [25] have described antibiotic resistance as one of the major threats to humanity in the coming century. Antibiotics or their metabolites enter wastewater treatment plants (WWTPs) and subsequently end up in surface waters through the sewage system, since WWTPs were not designed to remove antibiotics [22,[26][27][28]. Not only surface waters, but soils and sediments also suffer from the accumulation of antibiotics due to the usage of veterinary antibiotics and subsequent application of contaminated manure to the soil [20][21][22]27,29,30].…”

Intensification of biogas production using various technologies: A review

“…Intensification of biogas production can be also achieved by dewatering wastewater and sewage, optimization of physicochemical parameters such as pH, temperature, HRT, size of molecules submitted to fermentation, submitted to fermentation, configuration of a bioreactor, C/N ratio, intensity of the mixing process, and by employing immobilized biofilms or biofilters …”

“…Methanogenic microorganisms are highly sensitive to changes in pH in bioreactors. Excessively low pH can cause inhibition of AD, while very high pH can lead to the production of free ammonia, which is toxic to methanogenic microorganisms . The microorganisms participating in the process of methane fermentation, that is, hydrolytic, acidogenic, and methagenic microorganisms, have optimal pH ranges in which the maximum reaction efficiency is obtained.…”

Quantification of antibiotic resistance genes and mobile genetic elements in manure from dairy farms in California

“…The plasmid was also found to be integrated into transposons (Cain et al 2010). Huang et al (2019) reported abundance of ARGs and transposase genes, which were decreased during anaerobic digestion of swine manure. Most ARGs including sul genes were signi cantly correlated with transposase genes.…”

“…The authors found ARGs abundance varied among farms, and ARG concentrations generally did not correlate to average antimicrobial usage due to complex environmental factors. Most manure conditions were simulated at the bench scale, and only few analyzed commonly used practices in dairy farms (Flores-Orozco et al 2020;Huang et al 2019;Pei et al 2007;Selvam et al 2012;Sun et al 2016;Wang et al 2012). Wang et al (2012) simulated the environmental conditions of swine manure treatment by lab scale thermophilic composting and ambient temperature lagoon storage with modest aeration over a 48-day period.…”