Insights into bioaerosol contamination in the process of mineralized refuse mining: Microbial aerosolization behavior and potential pathogenicity

The landfill mining process is a main source of anthropogenic bioaerosol release, posing potential risks to the health of occupationally exposed personnel and nearby residents. In this study, microbial aerosolization behavior and potential pathogenicity during the landfill mining process were systematically investigated. The highest concentration of bacterial aerosols was measured in the refuse mining area, with a value of 5968 ± 1608 CFU/m3, while the highest concentration of fungal aerosols was 1196 ± 370 CFU/m3 in the refuse screening area. The bacterial and fungal aerosols were distributed primarily in the particle size ranges of 4.7-7.0 µm and > 7.0 µm, respectively. The pathogenic microbes Arthrobacter, Bacillus, Arthrobotrys and Aspergillus had high bioaerosol aerosolization capacities, with aerosolization indices of 100-329, 31-62, 2-14 and 1-11, respectively, when released from mineralized refuse. There are more than 100 types of pathogenic bacteria in bioaerosols. The microorganisms Lysobacter, Luteimonas and Mycolicibacterium, which carry virulence factor genes (VFGs) (pilG, Rv0440, pilT, etc.), can spread VFGs, aggravate bioaerosol pollution, and threaten the health of workers and nearby residents. This research will help further the understanding of bioaerosol contamination behaviors and potential pathogenicity risks from landfill mining activities.

Taxonomic and functional profiling of microbial community in municipal solid waste dumpsite

Understanding the microbial ecology of landfills is crucial for improving waste management strategies and utilizing the potential of these microbial communities for biotechnological applications. This study aimed to conduct a comprehensive taxonomic and functional profiling of the microbial community present in the Addis Ababa municipal solid waste dumpsite using a shotgun metagenomics sequencing approach. The taxonomic analysis of the sample revealed the significant presence of bacteria, with the Actinomycetota (56%), Pseudomonadota (23%), Bacillota (3%), and Chloroflexota (3%) phyla being particularly abundant. The most abundant KEGG categories were carbohydrates metabolism, membrane transport, signal transduction, and amino acid metabolism. The biodegradation and metabolism of xenobiotics, as well as terpenoids and polyketides, were also prevalent. Moreover, the Comprehensive Antibiotic Resistance Database (CARD) identified 52 antibiotic resistance gene (ARG) subtypes belonging to 14 different drug classes, with the highest abundances observed for glycopeptide, phosphonic acid, and multidrug resistance genes. Actinomycetota was the dominant phylum harboring ARGs, followed by Pseudomonadota and Chloroflexota. This study offers valuable insights into the taxonomic and functional diversity of the microbial community in the Addis Ababa municipal solid waste dumpsite. It sheds light on the widespread presence of metabolically versatile microbes, antibiotic resistance genes, mobile genetic elements, and pathogenic bacteria. This understanding can contribute to the creation of efficient waste management strategies and the investigation of possible biotechnological uses for these microbial communities.

Antibiotic resistance genes and heavy metals in landfill: A review

Landfill is reservoir containing antibiotic resistance genes (ARGs) that pose a threat to human life and health. Heavy metals impose lasting effects on ARGs. This review investigated and analyzed the distribution, composition, and abundance of heavy metals and ARGs in landfill. The abundance ranges of ARGs detected in refuse and leachate were similar. The composition of ARG varied with sampling depth in refuse. ARG in leachate varies with the distribution of ARG in the refuse. The ARG of sulI was associated with 11 metals (Co, Pb, Mn, Zn, Cu, Cr, Ni, Sb, As, Cd, and Al). The effects of the total metal concentration on ARG abundance were masked by many factors. Low heavy metal concentrations showed positive effects on ARG diffusion; conversely, high heavy metal concentrations showed negative effects. Organic matter had a selective pressure effect on microorganisms and could provide energy for the diffusion of ARGs. Complexes of heavy metals and organic matter were common in landfill. Therefore, the hypothesis was proposed that organic matter and heavy metals have combined effects on the horizontal gene transfer (HGT) of ARGs during landfill stabilization. This work provides a new basis to better understand the HGT of ARGs in landfill.

Response behavior of antibiotic resistance genes and human pathogens to slope gradient and position: An environmental risk analysis in sloping cultivated land

Soils, especially in farmlands, are key media for the transmission of antibiotic resistance genes (ARGs) and their hosts from the environment to humans. Sloping farmland is an important agricultural resource, but there lack of studies on the fate and risk of ARGs in sloping land. Also, the behavior and drivers of ARGs in response to slope gradient and position are unclear. Here, metagenomics was used to investigate the profiles of ARGs, mobile genetic elements, and microbial communities in soils from lands of five slope gradients (5°, 10°, 15°, 20°, and 25°) with two slope positions (uphill and downhill). Results showed that while the abundance (except 15°) and diversity (except 20°) of ARGs increased as the slope gradient increased, the diversity of ARGs with health risk, especially the high-risk ones, decreased. For slope positions, abundant and diverse ARGs were more likely to accumulate at downhill. Furthermore, 52 bacterial genera and 12 human pathogenic bacteria (HPB) species were identified as the potential hosts for ARGs with high risk, and abundant HPB species were also detected in the soils with low gradients at downhill. Moreover, the structural equation model analysis revealed that the slope gradient and the slope position have both direct and indirect effects on the abundance of ARGs. Further correlation analysis revealed that the slope gradient has a positive effect (p < 0.05) on nitrite nitrogen in the soils. Also, the slope position has a negative effect (p < 0.05) on total phosphorus and microbial nitrogen, while positively affected (p < 0.05) on particulate nitrogen and microbial carbon, which were the key factors driving the behavior of ARGs. Overall, this study provided comprehensive information on ARGs with health risks and their potential pathogenic hosts in sloping farmland. It can be important for controlling antibiotic resistance transmission and be consistent with the One Health framework.

Microbial methane cycling in a landfill on a decadal time scale

Landfills generate outsized environmental footprints due to microbial degradation of organic matter in municipal solid waste, which produces the potent greenhouse gas methane. With global solid waste production predicted to increase substantially in the next few decades, there is a pressing need to better understand the temporal dynamics of biogeochemical processes that control methane cycling in landfills. Here, we use metagenomic approaches to characterize microbial methane cycling in waste that was landfilled over 39 years. Our analyses indicate that newer waste supports more diverse communities with similar composition compared to older waste, which contains lower diversity and more varied communities. Older waste contains primarily autotrophic organisms with versatile redox metabolisms, whereas newer waste is dominated by anaerobic fermenters. Methane-producing microbes are more abundant, diverse, and metabolically versatile in new waste compared to old waste. Our findings indicate that predictive models for methane emission in landfills overlook methane oxidation in the absence of oxygen, as well as certain microbial lineages that can potentially contribute to methane sinks in diverse habitats.

Microbial contamination risk of landfilled waste with different ages

Landfills are reservoirs of antibiotic resistance genes (ARGs) and pathogens, and humans are exposed to these pollutants during extensive excavation of old landfills. However, the microbial contamination risk of landfilled waste with different ages has not been assessed. In this study, human bacterial pathogens (HBPs), ARGs, and virulence factors (VFs) were systematically determined using metagenomic analysis. Results showed that the abundance of HBPs, ARGs, and VFs increased with landfill age, the percentage of HBPs in refuse with deposit age of 10-12 years (Y10) was 23.75 ± 0.49%, which was higher than that in fresh refuse (Y0, 17.99 ± 0.14%) and refuse with deposit age of 5-6 years (Y5, 19.14 ± 0.15%), indicating that old refuse had higher microbial contamination risk than fresh refuse. Multidrug, macrolide, lincosamide, streptogramine, and tetracycline resistance genes were the primary ARGs, whereas lipooligosaccharides, type IV pili, and polar flagella were the dominant VFs in refuse. The HBPs showed a significant positive correlation with ARGs and VFs. Listeria monocytogenes, Salmonella enterica, Streptococcus pneumoniae, Acinetobacter baumannii, and Escherichia coli possibly possess both multiple ARGs and VFs and could be listed as high-risk HBPs in refuse. Mobile genetic elements, especially transposons, showed positive correlations with most ARGs and VFs, and they were identified as the primary factors accounting for the variations in ARGs and VFs. These findings will help understand the spread of ARGs and VFs in landfills and evaluate the potential risk of microbiological contamination in refuse of different landfill ages, thus providing guidance for preventing disease infection during landfill excavations.