Michael McDonald: the secret to survival in a heavily polluted system

In the UK, it is easy to feel that environmental pollution is a problem felt more severely elsewhere. Most news stories about pollution concern countries and continents very far from here. But this couldn’t be further from the truth.

Hundreds of years of mining for coal and metal have left an industrial legacy on the UK landscape, in the form of mine spoil heaps, and they’re wreaking acute damage on the environment even today.

Mine spoil heaps are large mounds of discarded rock and low-grade metal ore, left behind after excavating the earth for coal or valuable metals.

Once exposed, metals and sulfides in the excavated soil react with water and oxygen to form acidic compounds, which then dissolve in nearby streams, in a process known as metal leaching. The streams grow toxic and acidic, with unprecedented concentrations of dissolved metal ions. This acidic water flows away from the site, contaminating adjoining rivers and spreading the pollution far and wide, both geographically and up the food chain. 

This is acid mine drainage, and it poses a huge threat to human health and aquatic life.

A mine draining acid can devastate rivers, streams, and aquatic life for hundreds, and under the “right” conditions, thousands of years. - Earthworks 

Mine sites have drastically reduced microbial biodiversity 

Compared with natural conditions, where hundreds of different taxa are found to thrive, those in Benhar Bing allowed for very little diversity. Only between 10 and 13 different taxa (different biological groups) were observed. 

The microorganisms present have special capabilities to enable their survival 

Michael found the presence of sulphur cycling and metal tolerance genes. One of the microorganisms present, Metallibacterium, was found to have the ability to synthesise a diverse range of enzymes to counteract heavy metals and so could potentially be used for bioremediation. 

Their genomes are packed full of mechanisms allowing them to adapt to these conditions

Methane-producing organisms are present 

Michael also found the first ever evidence of methane-producing microorganisms (methanogens) in such acidic, pH 2.5, conditions. Methanogens are anoxic, meaning they cannot survive in the presence of oxygen; they’re usually hidden away in the seabed or within icebergs. The fact that they were found in this mine spoil heap was very surprising, as it was previously thought to be too extreme for their survival. 

This discovery adds another layer to the environmental impact of these sites; methanogens release the greenhouse gas methane, which drives climate change. 

Acid mine drainage is completely destructive environmentally, because it's so toxic and so hazardous, but also we've got this potentially added angle of greenhouse gas emissions.

Bioremediation

Further research can now explore potential applications of these extremophiles. There is hope that we can one day utilise these microorganisms’ superpowers to clean polluted sites, an application known as bioremediation. Michaels' chromosome reassemblies are an invaluable resource to support this. 

Microorganisms in these sites could potentially be used for metal extraction 

As we move away from fossil fuels and rely more on ‘greener’ technologies, such as electric vehicles, wind turbines and rechargeable batteries, we build a growing demand for metals. But mining for metals is incredibly environmentally damaging.

Michael postulates that we could instead use the microorganisms found in these sites to extract the metals we need. 

Instead of mining new sites for metals when we need them for electronics, for energy, can we recover metals from waste streams? Because we know from my chemical data that these effluents are full of metal! There are ways using communities or isolates of microorganisms that can recover the metal. Can we actually start thinking of it as a resource recovery, rather than just a pollution?

Metal extraction will require a huge shift in mindset. 

Michael explained how there is little profit involved in using the metals found in these mine drainage waste streams; the waste streams typically contain only cheap metals such as iron. Not only this, but mining is a grossly profitable industry and will not be easily reinvented. 

Culturing these microorganisms is also incredibly difficult. 

It is nearly impossible to replicate such extreme conditions in the lab, making them very difficult to culture. This is a huge bottleneck in microbiology. Michael describes them as an ‘untapped potential’, however, once we can successfully cultivate them, we could see immense breakthroughs.