A culture-based and culture-independent approach to the study of landfill leachate bacterial and archaeal communities.

The landfill is a convenient and affordable method of municipal solid waste (MSW) management. Landfill leachate contains a heavy load of pollutants and pathogens. Discharge of untreated leachate is the leading cause of surface and groundwater contamination and a threat to public and environmental health. To develop an efficient leachate treatment technology, an in-depth understanding of landfill chemistry and microbiology is essential. In the present manuscript, we conducted a comparative study of three different landfill leachate samples using cultivation-based and culture-independent molecular studies. We cultivated 85 species of aerobic, anaerobic bacteria and archaea from leachate represented by a total of 200 strains using extensive culturomics approaches. Twelve out of 200 cultivated strains of bacteria showed very low 16S rRNA gene sequence similarity (84-98.6%) with their closest relatives and could be the potential novel taxa, the first time cultivated from leachate. Members of the six genera only have 2-5 representatives from past studies from other habitats but first time cultivated from leachate. In addition to bacteria, we also cultivated and characterized different groups of methanogenic archaea. Our chemistry data indicate that leachate is a highly stressed ecosystem with an assemblage of many toxic wastes like sulfur, zinc, mercury, chromium, etc. 16S rRNA gene-based amplicon analysis showed the dominance of (30-55%) methanogens and haloarachaea. Our data suggest that archaea are the significant regulators of leachate ecology, and more in-depth studies with multiple leachate samples are required to understand their role in leachate nutrient cycling and the development of effective leachate treatment technology.

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Declaration of competing interest There is no conflict of interest among the authors for this manuscript.