Landfill sites: not just a load of rubbish

A capped landfill site

Collecting leachate from a capped landfill site

Far from being a load of rubbish, landfill sites should be considered one of the great untapped resources in the search for new enzymes for biotechnology, and could fuel more efficient biofuel production.

A new study by biologists at the universities of Liverpool and Bangor has, for the first time, identified the enzymes that degrade natural materials such as paper and clothing in landfill sites.

James McDonald, who led the research said: “There is a current impetus to search for new enzymes to improve biomass conversion processes. Our hypothesis is that, due to the volume of waste materials they hold, landfill sites represent a repository of unexplored biomass-degrading diversity. There is significant potential to identify new enzymes of ecological and biological significance.”

Cellulose and lignin occur naturally in plant-based materials and take longer to decompose than other waste products. As a result of this, the majority of landfill waste consists of lignin and cellulose. In their plant form, they can be used as the basis for biofuel production, and identifying more effective enzymes for this process would improve the yield from this source.

Scientists have been searching for a number of years for the most effective enzymes which break down the cellulose and lignin within the residual natural fibres. The obvious place to search has been in the rumen of sheep and cows, who eat grasses, and the guts of also other plant eaters such as elephants and termites.

Surprisingly perhaps, landfill sites share many of the same characteristics as the digestive systems of these animals: they are dark, anoxic or un-oxygenated spaces, with a high content of cellulose. It was therefore to landfill sites, which are artificially created ‘systems’, that this group of scientists turned to find new plant-degrading enzymes.

Professor Alan McCarthy from the University’s Institute of Integrative Biology said: “As we seek to increase waste recycling and reduce the amount of rubbish being disposed of in landfill sites, it is fascinating that these old sites are themselves proving to be a resource for the development of new technology.”

Within in the paper, the authors describe how they used the liquid or ‘leachate’ within landfill sites as a source of microbes to decompose cotton, and analysed not only the families or taxa of bacteria, but also identified which bacteria produce groups of enzymes to degrade cellulose.

Emma Ransom-Jones, a postdoctoral researcher and lead author of the study said: “Understanding exactly how the cellulose and lignin decompose, and the sources of the active enzymes in the process will enable us to determine ways to improve the degradation of waste in landfill sites, and potentially use this as a source for biofuel production.”

The paper ‘Lignocellulose-Degrading Microbial Communities in Landfill Sites Represent a Repository of Unexplored Biomass-Degrading Diversity’ is published in the journal mSphere.

DOI: 10.1128/mSphere.00300-17

Electron micrograph of microbes from a landfill site colonising and degrading cellulose’

Electron micrograph of microbes from a landfill site colonising and degrading cellulose

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