Plastics revolutionised the way we live. Plastics are food-safe, easy to manufacture, and sterile. They are also durable and long-lasting. This has made plastic an economical and attractive choice in a wide range of applications.

However, the persistence of plastics is also their drawback. Some plastics take hundreds of years to begin breaking down. Despite many plastics being recyclable, it is estimated that over 80% of the plastic manufactured will end up in landfill or as pollution, choking our oceans and terrestrial ecosystems. The COVID-19 pandemic has also increased the demand for single-use plastics, further exacerbating the problem. By 2050, it is estimated that there will be more plastic in the ocean than fish by weight.

Finding more sustainable, effective methods of dealing with our plastic waste is critical to our efforts to conserve the environment.

Seven main types of plastic are manufactured globally. This includes PET, which is a clear, strong, and lightweight plastic often used to make food packaging and drinks bottles. Many PET products are single-use, contributing to the catastrophic levels of plastic pollution the planet is now experiencing.

Fortunately, some microbes can break down the molecules – called ‘polymers’ – in PET, thanks to the similarity of these compounds to naturally occurring substances. The discovery of a bacterial species that produces enzymes capable of breaking down PET opened up a world of possibility for degrading this ubiquitous type of plastic. Since then, several bacteria have been identified that can use PET as their food source.

In their research, Dr Jay Mellies and his colleagues at Reed College and Willamette University identified a group of five bacterial species that together can break down PET and the byproducts produced during its degradation.

In a more recent study, they continued this work by comparing the genomes of 232 bacterial species that are related to the five bacteria they had previously studied. By comparing the genomes of the plastic-eating bacteria to their non-plastic-eating counterparts, the researchers isolated genes that confer this ability. These genes contain the instructions for building enzymes that break down PET and the byproducts produced during its degradation.

One of the team’s discoveries was an enzyme-producing gene that plays an important role in breaking down a specific byproduct of PET degradation. They achieved this by creating a strain of bacteria without a functioning version of this gene, and comparing it to the original bacterial strain.

Confirming their predictions, only the original bacteria broke down the PET byproduct. This enabled the researchers to identify and conduct a 3D structural analysis of the enzyme responsible for this process.

In addition to identifying several genes and their associated enzymes that degrade PET, Dr Mellies and his colleagues also discovered genes implicated in degrading other types of plastics and plasticisers.

Plasticisers are substances that are added to a range of hard plastics to make them softer and more flexible. For example, PVC is a type of hard plastic that can be softened with plasticisers to make shower curtains, flexible plastic tubing, and electrical wire insulation. Plasticisers are potentially harmful substances that have been implicated in a range of human, animal, and environmental health issues. Because plasticisers are not bound within the chemical structure of plastic polymers, they can leach into the surrounding environment.

As such, developing processes that can also break down the plasticisers within plastics is imperative. The researchers identified a range of genes in their group of bacteria that have the potential to break down plasticisers. The full suite of bacteria studied exhibited an incredible level of functional diversity and ability to degrade a range of polymers and plasticisers.

An important function involved in the effective degradation of PET is the ability of bacteria to adhere to a plastic surface and form a layer. This thin layer of bacteria is called a ‘biofilm’. Dr Mellies and his colleagues measured biofilm production in the bacteria they studied, and discovered a range of abilities.

The ability to produce biofilms is related to the production of a substance called ‘surfactin’, which triggers biofilm formation. The team recommend that including bacterial strains with enhanced surfactin production could increase the efficiency of processes developed to degrade mixed-plastic waste.

Dr Mellies suggests that the full suite of bacteria they investigated could together possess the ability to degrade the full range of plastic types, thanks to their functional diversity. His team’s research holds promise for developing mixed-plastic waste degradation using a specially selected group of bacterial species.

Plastic-eating bacteria could help us to achieve complete and safe plastic degradation, which is vital for solving the mounting global problem of plastic pollution.

Extreme weather events, such as droughts, have a significant effect on crop productivity. Drought places stress on plants, making many physiological functions more difficult or even impossible. As such, drought threatens agriculture’s ability to keep up with the food demands of a burgeoning human population. Much research has been undertaken to determine how plants and plant communities respond to drought conditions, providing a good indication of how they might respond under future climate change scenarios.

Plant roots interact closely with the soil microbial community surrounding them. In some cases, plants can gain some resistance to the effects of drought conditions through their association with soil microbes. Therefore, understanding how soil microbial communities respond to drought conditions is vital to predicting plant responses, and could be key to developing techniques that minimise the negative impact of droughts on plants.

Of the soil microbes, the drought response of soil fungi is particularly poorly understood. Fungal community responses – such as abundance, species diversity and community composition – often contrast the responses measured for plant communities under the same conditions. The apparently contradictory drought responses of fungal communities highlight the urgent need for additional research.

Dr Ari Jumpponen at Kansas State University aims to bridge this knowledge gap by examining soil fungal communities under experimental chronic drought conditions. Published in Fungal Ecology in 2021, his research demonstrates the high variability in how soil fungal communities respond to drought.

Alongside colleagues at Kansas State University, the University of Massachusetts, and Colorado State University, Dr Jumpponen applied a combination of powerful techniques to examine soil fungi in an established field experiment.

The Extreme Drought in Grassland Experiment – or ‘EDGE’ – consists of six experimental grassland sites in central and southwestern USA. At these sites, rainout shelters passively reduce the amount of rainfall reaching the ground by approximately 66% during the April to September growing season. This equates to approximately 40% reduction in the total annual rainfall.

For their study, Dr Jumpponen and his colleagues used two of the six EDGE field sites, each containing ten replicated plots with rainfall shelters – to simulate drought – and ten replicated plots without rainfall shelters – to provide non-drought plots for comparison. They took soil cores from each plot and used them to characterise the soil fungal community.

Using a combination of pure culture-based and advanced molecular analyses, they measured three features of the soil fungal community: community composition, species richness and species diversity. Community composition identifies which groups of fungi are present, while species richness describes the number of species present. Finally, species diversity captures both species richness and the frequency at which each species is observed in a community.

Dr Jumpponen and his colleagues found that soil fungal communities did not change compositionally as a result of drought conditions. Largely similar groups of fungi were present in both the experimental drought and non-drought plots. Surprisingly, both species richness and species diversity increased as a result of drought conditions – but only at the wetter of the two EDGE field sites.

The findings indicate that fungal communities are compositionally-resistant to drought, but their species diversity may be more sensitive. Dr Jumpponen suggests that the ability to withstand drought conditions may be due to dormant life stages, such as spores that are not sensitive to environmental conditions.

The results also suggest that fungal communities accustomed to higher rainfall may be more sensitive to drought conditions. In contrast, fungal communities accustomed to drier conditions may already be adapted to surviving in drought conditions.

The responses of fungal communities directly contrast those of plant communities under similar conditions. While fungal communities from wetter areas appear more sensitive to droughts, plant communities from arid grasslands are often more sensitive to droughts. Dr Jumpponen points out that this means that findings from drought studies using plant communities are likely to be of little benefit to understanding fungal communities. This could be due to a key difference in the life histories of plants and fungi. Unlike plants, fungi have communities with a large number of species that can remain dormant for long periods to cope with unfavourable environmental conditions.

Separating fungal groups based on their life histories may also reveal key differences in their ability to adapt to drought conditions. For example, plant-associated fungi may be more sensitive to droughts because they experience the direct effects of the drought conditions as well as the indirect effects of changes in plant physiology and communities.

These conflicting results exemplify the complexity of building a complete understanding of how soil fungal communities will respond to drought conditions in different habitats and climates.

The team’s study highlights the importance of further research on the responses of fungal communities to environmental change. Dr Jumpponen points out that it is still unclear whether their results indicate drought-resistance in active fungal communities, or that the compositional-resistance to drought is due to dormant fungi waiting for favourable conditions before resuming activity. Fungal communities may be able to respond rapidly to changing environmental conditions because of their ability to remain dormant, which has implications for future climate change predictions.

Understanding how fungal drought responses interact with and influence plant communities, especially in relation to plant-associated fungi, is a key avenue of research with value for both agriculture and conservation.

Finally, Dr Jumpponen and his colleagues suggest that studies across larger areas and over longer time periods could reveal other important factors for fungal community responses to drought and other environmental conditions.