Composting effect and antibiotic removal under a new temperature control strategy

Mechanisms for more efficient antibiotics and antibiotic resistance genes removal during industrialized treatment of over 200 tons of tylosin and spectinomycin mycelial dregs by integrated meta-omics

To mitigate the environmental risks posed by the accumulation of antibiotic mycelial dregs (AMDs), this study first attempted over 200 tons of mass production fermentation (MP) using tylosin and spectinomycin mycelial dregs alongside pilot-scale fermentation (PS) for comparison, utilizing the integrated-omics and qPCR approaches. Co-fermentation results showed that both antibiotics were effectively removed in all treatments, with an average removal rate of 92%. Antibiotic resistance gene (ARG)-related metabolic pathways showed that rapid degradation of antibiotics was associated with enzymes that inactivate macrolides and aminoglycosides (e.g., K06979, K07027, K05593). Interestingly, MP fermentations with optimized conditions had more efficient ARGs removal because homogenization permitted faster microbial succession, with more stable removal of antibiotic resistant bacteria and mobile genetic elements. Moreover, Bacillus reached 75% and secreted antioxidant enzymes that might inhibit horizontal gene transfer of ARGs. The findings confirmed the advantages of MP fermentation and provided a scientific basis for other AMDs.

Effects of two strains of thermophilic nitrogen-fixing bacteria on nitrogen loss mitigation in cow dung compost

Excavating nitrogen-fixing bacteria with high-temperature tolerance is essential for the efficient composting of animal dung. In this study, two strains of thermophilic nitrogen-fixing bacteria, NF1 (Bacillus subtilis) and NF2 (Azotobacter chroococcum), were added to cow dung compost both individually (NF1, NF2) and mixed together (NF3; mixing NF1 and NF2 at a ratio of 1:1). The results showed that NF1, NF2, and NF3 inoculants increased the total Kjeldahl nitrogen level by 38.43%-55.35%, prolonged the thermophilic period by 1-13 d, increased the seed germination index by 17.81%, and the emissions of NH3 and N2O were reduced by 25.11% and 42.75%, respectively. Microbial analysis showed that Firmicutes were the predominant bacteria at the thermophilic stage, whereas Chloroflexi, Proteobacteria, and Bacteroidetes were the predominant bacteria at the mature stage. These results confirmed that the addition of the isolated strains to cow dung composting improved the bacterial community structure and benefited nitrogen retention.

Preparation of high-temperature and low-temperature-resistant solid microbial agent for cattle manure fermentation and effect on composting

We used microbiology and molecular biology techniques to screen out high-temperature and low-temperature-resistant saprobiotics for compost and prepared a compound fermentation bacteria agent to rapidly ferment cattle manure into high-quality organic fertilizer in low-temperature season. Conventional composting and high-throughput techniques were used to analyze the changes of physical and chemical indexes and biodiversity in the process of composting, from which high and low-temperature-resistant strains were obtained, and high-temperature and low-temperature-resistant solid composite bactericides were prepared and added to composting to verify the effects of composite bactericides on composting. The conventional composting cycle took 22 days, and the diversity of microflora increased first and then decreased. Composting temperature and microbial population were the key factors for the success or failure of composting. Two strains of high-temperature-resistant bacteria and six strains of low-temperature-resistant bacteria were screened out, and they were efficient in degrading starch, cellulose, and protein. The high-temperature and low-temperature-resistant solid bacterial agent was successfully prepared with adjuvant. The preparation could make the compost temperature rise quickly at low temperature, the high temperature lasted for a long time, the water content, C/N, and organic matter fell quickly, the contents of total phosphorus and total potassium were increased, and the seed germination index was significantly improved. Improve the composting effect. The solid composite bacterial agent can shorten the composting time at low temperature and improve the composting efficiency and quality.

A Multi-Residue Analytical Method for Assessing the Effects of Stacking Treatment on Antimicrobial and Coccidiostat Degradation in Broiler Litter

Antimicrobial drugs and coccidiostat compounds are commonly used in poultry farming. These compounds are subsequently excreted and released into the environment via broiler litter (BL) and can re-enter the food chain as fertilizer or animal feed. Such residue in animal feed can encourage the appearance of antibiotic-resistant bacteria as well as toxicity. Most analytical methods used to identify and quantitate these drug residues are traditional, and are specific to some antimicrobials and present limitations in assessing complex matrixes like BL. The aim of this study was to develop a multi-residue analytic method for assessing 30 antimicrobial drugs and coccidiostats associated with BL. We investigated the presence and the effects of biotic stack treatment on the degradation of drug residue in BL. Liquid-liquid extraction (LLE) and solid phase extraction (SPE) were replaced by Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) clean-up steps and detected by liquid chromatography mass spectrometry (LC/MS/MS). Results show that a wide spectrum of residues were detected from 0.4 to 8.9 mg kg-1. Following lab-scale stacking treatment, tilmicosin and eight coccidiostats persisted in BL (26-100%). This research supports the need for better understanding, regulation, and management of the use of BL that might carry a high risk of residue drugs.

Urea addition as an enhanced strategy for degradation of petroleum contaminants during co-composting of straw and pig manure: Evidences from microbial community and enzyme activity evaluation

Alterations in microbial community succession patterns and enzyme activities by petroleum pollutants during co-composting of straw and swine manure with the supplementary nitrogen source are unclear. In this study, urea was added into co-composting systems, and the removal performance of petroleum, microbial enzyme activity and community changes were investigated. Results showed that the polyphenol oxidase and catalase activities which were both related to the degradation of petroleum contaminants were accordingly increased from 20.65 to 30.31 U/g and from 171.87 to 231.86 U/g due to urea addition. The removal efficiency of petroleum contaminants in composting with urea increased from 45.06% to 82.29%. The addition of urea increased the diversity and abundance of petroleum-degrading microorganisms, and enhanced microbial linkages. This study provides a novel strategy for the degradation of petroleum hydrocarbon as well as a new insight into the effect of urea on both microbial processes and composting phases.

Heat and carbon co-activated persulfate to regenerate gentamicin-laden activated carbon: Performance, mechanism, and safety assessment

Activated carbon enriched with high concentrations of gentamicin (ACG) was generated in the production process of gentamicin. Inappropriate handling methods for ACG not only squanders carbon resource, but also seriously hinders achieving global carbon neutrality and hazardous to human health. In the present work, thermal and carbon co-activated persulfate method (TC-PS) was developed to regenerate ACG with degrading gentamicin. The results showed that ACG was effectively regenerated by TC-PS, restoring the adsorption performance for gentamicin. When the treatment temperature was 80 °C, the persulfate dosage was 20 mM and the initial pH was 3.0, the degradation efficiency of gentamicin reached 100%. The HO• and SO4•- were the major reactive species for gentamicin degradation. The possible degradation routes of gentamicin were proposed and the safety assessment indicated that the produced intermediates during the regeneration process of ACG by TC-PS have insignificant impact on the biological and ecological environment.

Magnetic biochar accelerates microbial succession and enhances assimilatory nitrate reduction during pig manure composting

Biochar promotes microbial metabolic activities and reduces N2O on aerobic composting. However, the effects of magnetic biochar (MBC) on the microbial succession and N2O emissions during pig manure composting remain unclear. Herein, a 42-day composting experiment was conducted with five treatment regimes: pig manure without biochar (CK), 5 % pig manure-based biochar (5 % PBC), 2 % MBC (2 % MBC), 5 % MBC (5 % MBC) and 7.5 % MBC (7.5 % MBC)), to clarify the variation in functional microorganisms and genes associated with nitrogen and direct interspecies electron transfer via metagenomics. Fourier-transform infrared spectroscopy showed that MBC possessed more stable aromatic structures than pig manure-based biochar (PBC), indicating its greater potential for nitrous oxide reduction. MBC treatments were more effective in composting organic matter and improving the carbon/nitrogen ratio than PBC. The microbial composition during composting varied significantly, with the dominant phyla shifting from Firmicutes to Proteobacteria, Actinobacteria, and Bacteroidota. Network and hierarchical clustering analyses showed that the MBC treatment enhanced the interactions of dominant microbes (Proteobacteria and Bacteroidota) and accelerated the composting process. The biochar addition accelerated assimilatory nitrate reduction and slowed dissimilatory nitrate reduction and denitrification. The Mantel test demonstrated that magnetic biochar potentially helped regulate composting nutrients and affected functional nitrogen genes. These findings shed light on the role of MBC in mitigating greenhouse gas emissions during aerobic composting.

Characteristics of gut bacterial microbiota of black soldier fly (Diptera: Stratiomyidae) larvae effected by typical antibiotics

As agents in an emerging technology, Hermetia illucens (Linnaeus, 1758) (Diptera: Stratiomyidae) larvae, black soldier fly, have shown exciting potential for degrading antibiotics in organic solid waste, a process for which gut microorganisms play an important role. This study investigated the characteristics of larval gut bacterial communities effected by typical antibiotics. Initially, antibiotics significantly reduced the diversity of gut bacterial species. After 8 days, diversity recovered to similar to that of the control group in the chlortetracycline, tylosin, and sulfamethoxazole groups. Proteobacteria, Firmicutes, and Actinobacteriota were the dominant phyla at the initial BSFL gut. However, after 4 days treatment, the proportion of Actinobacteriota significantly decreased, but Bacteroidota notably increased. During the conversion process, 18, 18, 17, 21, and 19 core genera were present in the chlortetracycline, sulfamethoxazole, tylosin, norfloxacin, and gentamicin groups, respectively. Pseudomonas, Actinomyces, Morganella, Providencia and Klebsiella might be the important genera with extraordinary resistance and degradation to antibiotics. Statistical analyses of COGs showed that antibiotics changed the microbial community functions of BSFL gut. Compared with the control group, (i) the chlortetracycline, sulfamethoxazole, and tylosin groups showed significant increase in the classification functions of transcription, RNA processing and modification，and so on, (ii) the norfloxacin and gentamicin groups showed significant increase in defense mechanisms and other functions. Note that we categorized the response mechanisms of these classification functions to antibiotics into resistance and degradation. This provides a new perspective to deeply understand the joint biodegradation behavior of antibiotics in environments, and serves as an important reference for further development and utilization of microorganisms-assisted larvae for efficient degradation of antibiotics.

Co-occurrence pattern of ARGs and N-functional genes in the aerobic composting system with initial elevated temperature

Animal manure is known to harbor antibiotic resistance genes (ARGs). Aerobic composting is a prevalent cost-effective and sustainable method to treat animal waste. However, the effect of initially elevated temperature on antibiotic resistome during the composting process is unclear. In this study composting was subjected to initial external heating (EHC) for a period of 5 days compared to conventional composting (CC). After composting ARGs abundance was significantly reduced by 2.43 log in EHC and 1.95 log in CC. Mobile genetic elements (MGEs) also exhibited a reduction of 1.95 log in EHC and 1.49 log in CC. However, during the cooling phase, the genes resisting macrolide lincosamide and streptogramin B (MLSB) rebounded by 0.04 log in CC. The potential human pathogenic bacteria Pseudomonas (41.5-61.5%) and Actinobacteria (98.4-98.8%) were significantly reduced in both treatments and the bulk of targeted antibiotics were eliminated by 80.74% in EHC and 68.98% in CC. ARGs and N-functional genes (NFGs), mainly denitrification genes, were carried by the same microbial species, such as Corynebacterium sp. and Bacillus sp., of the dominant phylum. Redundancy analysis (RDA) revealed that CC microbial communities played a key role in the enrichment of ARGs while in EHC the variation of ARGs was attributed to the composting temperature. The number of high-risk ARGs was also lower in EHC (4) compared with CC (6) on day 30. These results provide insight into the effects of an initially enhanced temperature on ARGs removal and the relationship between ARGs and NFGs during the composting process.