​The power of biofilm engineering: one plus one does not always make two

Biofilms are ubiquitous in aquatic systems, where they play essential ecological roles in nutrient cycling, biogeochemical processes, and surface colonisation dynamics. In fact, marine bacteria exist predominantly within biofilms rather than as free-floating (planktonic) cells. These biofilms are often complex, composed of communities rather than single taxa. Hence, biofilms are dynamic systems influenced by interactions within the microbial community and by external environmental conditions. The composition and structure of marine biofilms dictate their overall phenotype, which, in turn, affects biological processes such as the subsequent settlement of eukaryote larvae and spores.

Engineering marine biofilms with tailored functional properties

Biofilms provide bacteria with a stable and protective environment suitable for growth and reproduction. Over millions of years, selective pressures have optimised the physical and chemical properties of biofilms to enhance the fitness of the bacterial engineers.

What, then, if we could impose our own selective pressures to guide marine biofilm formation toward specific, desirable outcomes?

Our research suggests that by applying the principles of hypothesis-driven or random community assembly, it may be possible to engineer bacterial communities to produce biofilms with tailored properties. This may involve the deliberate selection of specific bacterial strains for desirable traits or by specific selective pressures acting upon randomly-assembled biofilm communities under controlled conditions. We refer to these community assembly approaches as “Bottom-up” and “Top-down”, respectively, as illustrated in Figure 1.

We focus here on an example of marine biofouling control. However, the ability to select, evolve, or assemble microbial communities with specific functions opens doors to numerous applications across medicine, industry, agriculture, and environmental management.

Marine biofouling: problems and control strategies

Marine biofouling is the accumulation of animals, plants, and microbes on submerged surfaces, such as ship hulls and underwater infrastructure. This results in increased drag, corrosion, fuel consumption, and maintenance costs.

The growth of so-called ‘macrofouling’ communities of barnacles, mussels, etc. is driven by the settlement of their planktonic larvae. In many cases, larval settlement is influenced by pre-existing microbial biofilms on surfaces. Depending on the biofilm’s composition, larval settlement can be either positively or negatively influenced. Over decades, scientists have tried to identify specific bacterial taxa or their metabolites that can induce or inhibit larval settlement. The goal has been to incorporate functionality into antifouling coatings to reduce the reliance on harmful biocides. So far, however, no ‘magic bullet’ has been discovered that can prevent biofouling.

A paradigm shift: biofilm-based protective coatings

Instead of treating bacterial taxa or their functional metabolites as individual ingredients in an otherwise synthetic antifouling coating, could it be possible for bacterial communities to produce biofilms that are inherently fouling-resistant? Are they, themselves, fouling-control coatings? If we are to achieve such ‘living coatings’ without genetic modification, then only one option exists – directed biofilm community assembly. Communities of bacteria can have properties, including biofilm phenotype, that would not be easily predicted from knowledge of the individual component taxa. In other words, when brought together in a community, the traits of the community can be different from the sum of the parts: In biofilms, one plus one does not always make two. We call these emergent properties, and our research has aimed to identify communities that produce, as an emergent property, the ability to protect surfaces from macrofouling. A biofilm-based antifouling coating can function as an inert physical barrier, akin to the foul-release coatings currently in use, simply preventing larvae and spores from accessing the underlying surface. However, unlike a synthetic coating, a biofilm-derived coating could be self-sustaining, dynamically regenerating over time. Crucially, it would be non-biocidal and environmentally neutral, operating as a physical barrier to larval settlement rather than through chemical toxicity.

A case study: community assembly and selection for antifouling properties

To realise this concept, we assembled microbial communities based on taxa isolated from ship hulls, navy gliders, and algae. Using a bottom-up assembly approach, communities were subjected to various selective pressures, including different incubation temperatures. We found that some assembled communities exhibited higher tolerance to temperature fluctuations than the single taxa they included. Additionally, we identified bacterial isolates and a community capable of preventing larval settlement of the barnacle Amphibalanus improvisus in short-term laboratory assays. To improve the longevity of the communities in field conditions, we also applied directed evolution towards enhanced resistance to invasion by Pseudoaltermonas tunicata, a model species for biofilm invasion studies.

Broader applications and future directions

Our findings have highlighted the potential of biofilm engineering, using only wild-type taxa, to achieve specific functional materials. While this work represents an early-stage proof of concept, the approach has broader implications beyond marine antifouling. With sufficient data, machine learning algorithms could be employed to predict useful emergent properties that we cannot currently foresee, thereby rationally guiding community assembly processes. Such a toolkit would revolutionise materials science by providing a means to develop dynamic, self-sustaining and environmentally friendly biofilm-based materials and provide new avenues towards bioremediation and environmental management rather than relying on chemical formulations.

If you are interested in contacting the authors of this work, please contact Nick Aldred.