The theme of World Microbiome Day 2021 on 27th June is ‘sustainability’. We often think of microbes, such as bacteria, in terms of direct physical health, but this year’s event aims to raise awareness of the importance of microbes in maintaining healthy global ecosystems. Microbes influence the health and balance of the environments people live in, including effects that the gut microbiome - the collection of microorganisms in the gastrointestinal tract - has on human health. Taking a wider view, microbiomes collectively contribute to sustaining food systems, clean environments and mitigating climate change. Ultimately, these factors all contribute to the health of animals and humans globally1.

The role of microbiomes

The human microbiome includes the ecosystem of microorganisms, including bacteria, fungi, viruses and protozoa, which inhabit body systems and influence how the body functions. This includes the gut microbiome, which has the greatest number of cells in the large intestine2. The large intestine is home to a diverse and dense community of microbes, dominated by carbohydrate-degrading anaerobes. The gut microbiome has diverse functions and interactions in gastrointestinal health, as well as non-digestive functions such as immunity and cognition. There has been co-evolution of the gut microbiome and the human host, suggesting the importance of the gut microbiome when looking into the future of public health. The environment and soil microbiome has had a part to play in the development of the human microbiome and continues to do so. Therefore, the preservation of microbiomes in the environment is important for maintaining the wellbeing of the planet, plants, humans and other animals2. The human microbiome directly corresponds to the established United Nations’ Sustainable Development Goals (SDGs), such as ‘SDG 3’ for good health and wellbeing3.


Microbiomes are equally prevalent in other kingdoms, such as the rhizosphere in plants. They play a significant role in disease, health, growth and development of organisms. Both the gut microbiome and the plant rhizosphere are open systems, hosting trillions of microbes. Although differences are seen between the composition of the two, there are similarities in the function of the microbiomes, particularly related to nutrient acquisition, protection against infection and immune modulation4. Plants colonised by a large and diverse number of microbes, when eaten by animals, can transfer microbes from plant tissue to the gut microbiome of animals with a beneficial effect. Similarly, opportunistic human microbes can transfer to plants. It is important to understand how the ecosystems between kingdoms - and the microbiomes within them - interact for the goal of improving agricultural sustainability and human health4.

Microbial transfer and environmental influence

Nutrients and microbes from the food humans eat affect the gut microbiome, and in turn, human health. Industrial agriculture and an increasing global population have led to monoculture, as well as the increasing use of pesticides and fertilisers to maintain yield5. These factors are contributing to poor microbial diversity in the soil and the subsequent loss of microbial populations. Considering the sustainability of food systems and the gut microbiome, typical Western diets, with increased meat consumption and low fibre intake, tend to result in high carbon emissions, as well as effects on the gut microbiome due to more fermentation of protein in the colon and the metabolites produced5. In addition, many common foods in Western diets are highly processed and transported internationally, further increasing carbon output. Food systems are highly complex and while the effect on the gut microbiome should be considered, there are a variety of other considerations to be made such as socioeconomic and those related to public health concerns.

Urban City Scape

The human microbiome can be affected by contact with animals, surfaces, food and water, contact with other people and inhalation6. Similarly, the human gut microbiome can influence resistance to pathogens and parasites, through environmental exposure, by interacting with the immune system. The built environment is also a source of microbial transfer. Work environments such as offices and factories are reported to affect the oral, nasal and skin microbiome of workers6. A healthy coexistence of animal, human and environment microbiomes could be a potential intervention to optimise microbiome exchange between humans and their environment. This opens up the potential for health policy in the future to take into the environment and human microbiomes into consideration6.

In summary, there are significant ways in which microbes underpin global sustainability, making a deeper understanding of microbiomes all the more important. There is a relationship between food, health and the gut microbiome. The nutrient quality of food and surface microbes are related to the environment and soil microbiomes. It is a complex multilayer interaction between the gut microbiome, food consumed and health effects. Therefore, greater consideration of food systems will have a key role to play in the long-term sustainability of health, and the nature of the gut microbiome7. Preserving the environment with sustainable microbiomes and enabling our continued reliance on microbes for food production and health will need to be a part of the sustainability discussion into the future.

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