12 Nov 2019

Microbes: climate change accelerator or saviour?

Alli Cartwright weighs the heroes and villains of climate change - microbially speaking

Unless you’ve been living in a bubble (or in the White House) you’ll have heard of climate change and hopefully agree with me that humans have advanced the natural process with emissions of greenhouse gases. Greenhouse gases, including water vapour, carbon dioxide, methane, nitrous oxide and ozone, can be natural or released by human activity and trap heat in the atmosphere [1]. Our climate is warming, which is predicted to cause sea levels to rise 36-87 cm by 2100 assuming global warming is limited to 2 ℃, but we are likely to have a 3-4 ℃ rise if we continue as before [2].

The UK has pledged to reduce net carbon emissions to 0 by 2050 but in 2016 the UK’s emissions were 784 million tonnes so we have a long way to go [3]. Proposed solutions include green energy, reducing emission from transport and increasing plant biomass. Recently planting trees has become a focus after Jean-François Bastin and team calculated that 67% of human derived carbon emissions could be captured in the living tissue of trees if 0.9 billion hectors of land was planted [4]. While this study may have simplified matters and suggests a ‘miracle cure’, our energy would be best spent combining different strategies to reduce greenhouse gas emissions. With scientists trying to find solutions to fix our planets, I can’t help but wonder how microbes fit into climate change and whether they will make matters worse or better.

Could microbes accelerate climate change?

Since early high school, I have appreciated the importance of microbes to nutrient cycles whereby soil-dwelling microbes release carbon dioxide through decomposition [5]. As temperatures rise, microbial action speeds up causing quicker decomposition of organic matter and a faster release of carbon dioxide to the atmosphere thus accelerating global warming. Additionally, the rise in temperatures allows previously frozen organic matter to be decomposed – such as a frozen mammoth carcass released from retreating ice.

Rising temperatures also cause permafrost, the frozen soil layer, to thaw forming lakes under ice. In this water decomposition takes place to release carbon dioxide and methane [6]. Vigneron et al (2019) showed that regardless of season, the permafrost lakes release carbon dioxide. In summer this is from the activity of aerobic decomposers from phylum actinobacteria and class betaproteobacteria and in winter anaerobic decomposers from phyla planctomycetes, chloroflexi, and class deltaproteobacteria release carbon dioxide [6]. In winter methanogenic microbes also dominated releasing methane as a biproduct [6]. All methanogenic microbes globally account for 75% of the world’s natural methane emissions [7]. Methane as a greenhouse gas is 25x more efficient at trapping heat than carbon dioxide and as temperatures rise, so does the activity of methanogenic microbes thus multiplying the effect [7, 8].

Can microbes help mitigate climate change?

While some microbes can speed up the release of greenhouse gases, their shear diversity also means other microbes can trap greenhouse gases. Soil microbes are able to prevent the release of carbon dioxide to the atmosphere in the process of carbon sequestration [5]. Microbes themselves are made of carbon and so locked up carbon increases with the abundance of living soil microbes. Even when microbes are involved in decomposition releasing carbon dioxide, some of the organic matter will be stored in the microbe. Globally soils hold 3 times more carbon than the atmosphere and farmland soils alone could store 50-80% more carbon if fungi and bacteria are increased in the soils by e.g. crop rotation, restoring degraded land or growing perennial crops [9, 10]. Additionally, restoring wetlands could prevent the loss of 5000-20000 g of carbon a year by reducing decomposition and providing more water to absorb carbon [9].

Natural microbes can protect against climate change, but can also be engineered to remove greenhouse gases while making industrial products and fuel. At this year’s FEMS Congress, Nigel Minton from the University of Nottingham outlined some of the special microbes they are using to trap carbon dioxide. The first he talked about was the Betaproteobacterium Cupriavidus necatar which turns carbon dioxide into useful industrial chemicals such as butyrate (anti-inflammatory fat) and ethanol [11]. He noted that once strains have been found with desirable properties, they can be engineered to maximise production. His team have altered the bacterium Acetobacterium woodii to maximise carbon dioxide conversion to acetate and can make 51 g/l in less than 4 days [11] replacing the standard method where wood pulp is added to acetic acid. These engineered microbes are valuable to industry and help in our fight against climate change.

Although the future is set to be warmer, we still have the opportunity to make changes and prevent making matters worse. Microbes are often ignored but they are intrinsically linked to the climate. They have the potential to accelerate or slow global warming. Undoubtedly, any solution alone will not be enough and so multiple solutions will need to be instigated together. We need a solution quick!

Alli Cartwright

ECS Communications Officer

Microbes: climate change accelerator or saviour?

Could microbes accelerate climate change?

Can microbes help mitigate climate change?

Further reading