Unravelling mechanisms underpinning adaptation in Bacillus subtilis biofilms

Microbial biofilms are the most prevalent form of microbial life. Biofilms are complex, organized communities of microorganisms encased in a protective glue, or "matrix", consisting of a sticky combination of proteins, sugars, fats, and DNA. This matrix protects the organisms living in the biofilm, shielding them from external attack and environmental changes. The result is a highly resilient community, with wide implications for industry and health. For example, chronic infections in hospital settings often resist treatment because the microbial protagonists encase themselves in a biofilm, whether on a catheter or a hip replacement joint, with the matrix also preventing some antibiotic access. Biofilm communities also have positive benefits: they drive all wastewater treatment and promote growth in most crop plants. Significant research effort is targeted to prevent, detect, manage, and ultimately engineer microbial biofilm communities so that they can be deployed when beneficial, or removed when detrimental.

This project addresses the challenge of understanding the composition, and changes in composition, of the matrix produced by a microorganism, Bacillus subtilis. B. subtilis is widespread in the environment, where it needs to withstand a wide range of conditions, from the low temperatures of soil to the high temperatures found in compost heaps and desert sands. Our programme is underpinned by a lucky observation: that our model B. subtilis isolate dramatically changes its matrix composition in response to temperature. This suggests that B. subtilis can adapt and change its local environment in response to external cues. Our first overarching aim is to determine the precise mechanisms controlling this change in composition with the ultimate goal of generating a given matrix composition - and behaviour - on demand. Our second overarching aim is to determine whether and how matrix composition matters: does a given matrix provide better protection against competitor organisms? Does another matrix let B. subtilis survive droughts, or explore and colonise the environment? To do this we will use methods that allow us to tightly control the environment in time and space, moving away from petri dishes and towards more realistic and complex environments.

Potential application areas include agriculture, where B. subtilis is already used as a probiotic organism that supports crop production. Our research will point towards phenotypes and therefore strains of B. subtilis that will perform optimally in a given environment. A second is in the production of ingredients for fast-moving consumer goods, e.g., skincare formulations. B. subtilis is a workhorse microorganism used to produce e.g. the enzymes found in washing powders, but also the molecule poly-gamma-glutamic acid (PGA), which is used as a thickener in cosmetics. We will focus on PGA production in our work, because the biofilm matrix switches to a PGA-rich form at high temperatures. If we understand the mechanisms that cause B. subtilis to switch to PGA production, we can increase yields of this industrially important molecule.

Our programme sits in the BBSRC research spotlight area of plant health, the development of novel crop protection strategies, and a better understanding of the roles of soils, including their microbial communities and symbionts in resilient crops. The BBSRC, alongside InnovateUK, is also investing £7.5M over the next five years into the National Biofilm Innovation Centre, recognising the potential of microbial biofilms as an engine for innovation. Our proposed programme is of direct relevance to this strategic priority area.