A veterinarian point-of-view:
Microbes are everywhere: in the soil, on rocks, in and on us, animals, plants, etc. All this is well known. But what is less well known is that these microbes often live in a particular way, inside a gel and attached to any surface or interface. This particular way of living is called a biofilm and can be seen as a fortress that makes its inhabitants more resilient, organised and productive than other microbes that live freely in air or water. Biofilms can be considered as the living skin of ecosystems and are, in fact, real cities of microbes composed of hundreds of species that interact as in a mini-ecosystem.
Abundant biofilm growing on an immersed piece of wood –
Un biofilm conséquent évoluant sur un morceau de bois immergé dans un lac. (© Hugo Sentenac)
The main aim of our paper, published in the British Ecological Society's journal Functional Ecology, was to review the roles that biofilms play in our health and that of animals, plants and entire ecosystems. We found that biofilms, although intensively studied, were still viewed from the perspective of only one scientific discipline at a time, whether it be human or veterinary medicine, ecology, biodiversity or evolution, or bioengineering. We wanted to break down these disciplinary silos, as they hinder our understanding of the global importance of biofilms on Earth. Yet, in an era of rapid global change, it is essential to give the biofilm life form its rightful place in understanding the relationships between the structures and functions of microbial communities in all kinds of environments, if we are to ensure sustainable development.
In summary, biofilms can have negative and positive roles, depending on the context. But overall, biofilms are important for our health: for example, the microbes that live in our gut are essential for our growth and the normal functioning of our bodies and those of animals and plants. A balanced and diverse biofilm protects us from diseases such as obesity, autism or cancer, and even from infectious diseases, directly by providing a barrier effect, and indirectly by instructing our immune system. Disrupted biofilms (dysbiosis) are more permeable to pathogens. The same is true for almost all animals and plants, and probably all multicellular organisms which are in fact superorganisms composed of many microbial cells, mainly in the form of biofilms.
Biofilms in the environment are also essential not only for the normal functioning of ecosystems (e.g. they provide oxygen and food for many organisms by using solar energy as plants do), but also for protecting their health (and indirectly ours) by biodegrading pollutants in water and soil, limiting erosion and ensuring soil fertility, among other things.
A secondary objective of our paper was to highlight the gaps in our knowledge of biofilms. We found that there is still much to learn about the impacts of climate change (warming and drought), pollution, habitat destruction/degradation, our urbanised lifestyle, our use of antibiotics, etc. on the biofilms that live with us or in the environment, and ultimately on our health. Most studies have focused on one type of biofilm and one type of stressor. In nature, however, biofilms are exposed to many stressors simultaneously. Furthermore, while we know that many human pathogens responsible for waterborne diseases can be harbored or killed by biofilms, depending on their composition, virtually nothing is known about pathogens responsible for emerging diseases in wildlife and plants. This is in stark contrast to the major obstacle to sustainable development posed by the growing number of emerging infectious diseases!
The crucial question is when biofilms will cease to fulfill the roles they currently provide because global changes (climate change, land use change, nutrient and chemical pollution, etc.) influence the way they are composed and function. Which roles are affected first, and by what exactly? Getting accurate answers is extremely complex, and we certainly won't get them if we continue to ignore biofilms in research, conservation practices and environmental policies.
In an attempt to shed light on some of these questions, our team in the GloMEc (Global Change in Mountain Ecosystems) project is studying the composition of biofilms in high-altitude lakes in the Pyrenees and assessing the impacts of climate change, fish introduction, pollution, pastoralism and tourism. In such environments, biofilms may be one, if not the most dominant compartment of the ecosystem, and the only basis for food webs in the absence of vegetation. They are the food of tadpoles, for example. We also want to see if there are links between the composition of biofilms and the dynamics of infectious diseases of amphibians, such as panzootic amphibian chytridiomycosis, which is ravaging frogs and toads worldwide, including in our mountains.
The initial results show that even under such harsh conditions, biofilms are much more diverse than the water microbiome, with hundreds of species detected in less than one ml of biofilm. From this work and our review article, it is clear that biofilms should be considered as ecosystems, with their own health, that is their own structure, productivity and resilience. Biofilm health should be closely monitored to ensure a sustainable future.
The abstract from the paper:
Biofilms are matrix-enclosed communities that represent the most dominant and active mode of microbial life on Earth. Because biofilms are inherently more productive than any equivalent planktonic community, they are of great relevance to all environments they inhabit. However, their existence and importance are still poorly known by the general public, conservation practitioners and environmental policymakers.
Most micro-organisms of multicellular organisms (including humans, animals and plants) occur in the form of true biofilms or biofilm-like structures that play vital roles in their development, physiology and immunity. Conversely, some biofilms can have a negative effect on host health.
Biofilms growing on non-biological surfaces are essential components of many terrestrial and marine ecosystems: they form the basis of food webs and ensure nutrient cycling and bioremediation in natural systems. However, environmental biofilms can promote the persistence of human pathogens, produce harmful toxins, foul and corrode surfaces in natural and man-made settings; all of which can have significant health and economic implications.
There is a knowledge gap about the roles of biofilms in the epidemiology of wildlife emerging infectious diseases, yet these pose a major threat to public health, biodiversity and sustainability. The drivers of global environmental change all affect biofilm structure and functions. The consequences for host and ecosystem health are, however, poorly understood. While the concept of a healthy microbiome (as opposed to dysbiosis) is emerging in medicine and conservation biology, the concept of a healthy biofilm remains to be defined in environmental sciences.
Here, we use an integrative approach to (a) review current knowledge on the roles of biofilms growing on biological and non-biological interfaces for the health of multicellular organisms and ecosystems, and (b) provide future research directions to address identified knowledge gaps. Giving the biofilm life-form its full importance will help understand the effects of global environmental change on these communities and, in turn, on human, animal, plant and ecosystem health.