Fate of integrons, antibiotic resistance genes and associated microbial community in food waste and its large-scale biotreatment systems.

The prevalence and dissemination of antibiotic resistance genes (ARGs) have been globally gained increasing concerns. However, the fate and spread of ARGs in food waste (FW) and its large-scale biotreatment systems are seldomly understood. Here, we investigated the initial and biologically treated FW in two major FW treatment systems of aerobic fermentation (AF) and anaerobic co-digestion (AcoD) processes. The total relative abundances of integrons and ARGs significantly increased from initial FW to treated FW. Among targeted ARGs, ermB and strB were predominant ARGs, which accounted for 52.58-95.28% of total abundance across all samples. Mantel test indicated that integrons (intl1 and intl2) were positively and significantly correlated with detected ARGs (Mantel test, r = 0.24, p < 0.05), suggesting integrons display significant contributions on driving ARG alteration during FW treatment processes. RDA results indicated that blaOXA, strB and blaTEM were more likely to be proliferated by potential host of Firmicutes (96.55-99.77%) in initial FW, while blaCTX-M and mefA were potentially enriched by Proteobacteria (17.12-49.82%) in AF system and ermB, sul1, aadA and tetQ were possibly enhanced by Bacteroidetes (27.43-43.71%) in AcoD system. Consideration of the higher enriched abundance of total ARGs (66.88 ± 87.34 times) and the used inoculum sludge in AcoD-treated system, the resource utilization of anaerobically digested products should draw our more attentions. These findings would deepen our understanding of prevalence and proliferation of ARGs in FW treatment systems and serve as a foundation for guiding the application of biologically treated FW.

Functional characteristic of microbial communities in large-scale biotreatment systems of food waste.

In order to evaluate microbial community structure dominated metabolic function profiles in large-scale food waste (FW) biotreatment systems, bacterial, archaeal and fungal community associated with metabolic function in high-temperature aerobic fermentation (AF) and anaerobic co-digestion (AcoD) processes were comprehensively investigated in this study. The qPCR results showed the higher gene copies of bacteria and fungi in initial and AF-treated FW compared with AcoD-treated FW, as well as bacteria and archaea in AcoD-treated FW were highly abundant among detected samples. Furthermore, the total abundances of archaea ((1.18-4.88) × 106 copies/ng DNA) in AcoD system were 2-3 orders of magnitude higher than that in other samples (P < 0.01), indicating active archaeal activity in AcoD system. Correlation analysis of microbial community and metabolic function indicated that the higher abundances of Kazachstania, Pyrobaculum, Sulfophobococcus, Lactobacillus and Candida in initial FW had close linkages with lipid metabolism (P < 0.05). Abundant Aspergillus, Staphylococcus, Pelomonas, Corynebacterium, Faecalibacterium, Methanobacterium and Xeromyces in AF system were positively and significantly correlated with high metabolic activities of energy metabolism, carbohydrate metabolism, amino acid metabolism, fatty acid metabolism, glycosaminoglycan degradation, sulfur metabolism and nitrogen metabolism. As for AcoD system, dominant genera Methanosaeta, Methanoculleus, Methanobacterium, Fastidiosipila, Rikenellaceae RC9, Bifidobacterium and Xeromyces had close relationships with metabolism of cofactors and vitamins, energy metabolism, methane metabolism, carbohydrate metabolism and glycosaminoglycan degradation (P < 0.05). These results are expected to improve the metabolic efficiency by functional microorganism in different large-scale FW treatment systems.

Insights into factors driving the transmission of antibiotic resistance from sludge compost-amended soil to vegetables under cadmium stress.

Sludge compost is often used as a fertilizer for crops, although it might be enriched with antibiotic resistance genes (ARGs) and heavy metals that cannot be removed through composting. A robust understanding of the factors affecting the transmission of ARGs to vegetables grown in soils treated with sludge products is lacking. In this study, target ARGs in the bulk and rhizosphere soils and endophytes of shallots under heavy metal stress (i.e., Cd) were assessed, and the factors driving the transmission of ARGs were identified. Cd stress resulted in an increase in the relative abundances of target ARGs in the bulk and rhizosphere soils and endophytes. The driving factors were different in soils and plants under different degrees of Cd stress. The fungal community composition was the main driving factor of ARG variation in both bulk and rhizosphere soils. Moreover, endophytic bacteria played a crucial role in transferring ARGs to plants. Higher Cd stress promoted the transfer of most target ARGs from the below-ground plant parts to the above-ground parts. These findings indicate that application of sludge contaminated with heavy metals, such as Cd, can facilitate the dissemination of ARGs into vegetables, which must be considered while assessing the risks to public health.