HENRY, N. | Search bioRxiv

bioRxiv2025

Experimental and theoretical approaches reveal that antimicrobial blue light killing efficiency decreases with biofilm growth in a Pseudomonas aeruginosa model.

Recently, the use of antimicrobial blue light (aBL) has gained interest across various applications. However, a comprehensive framework that addresses the key factors driving bacterial photoinhibition remains lacking--particularly concerning biofilms, the predominant bacterial lifestyle. The goal of this work was to evaluate the potential of photokilling in this wide-spread microbial adherent community type, and to decipher the specific mechanisms at stake. To investigate aBL killing efficiency, we conducted experiments in a Pseudomonas aeruginosa biofilm model using a well-defined millifluidic device that allows real-time microscopy and quantitative analysis of a living biofilm under local irradiation at a defined light dose. In addition, we developed a theoretical model for light-biofilm interaction that accounts for the threedimensional structure of the bacterial biofilm. To inform our model, we examined the light doseresponse in isolated cells and found a profile indicative of a multi-target mechanism of lethality. By comparing the experimental and theoretical results, we identified a loss in killing efficiency as the biofilm grows, due in part to the increase in thickness of the living material inherent to this mode of development. Our findings also highlight a reduction in the intrinsic bacterial sensitivity to blue light as biofilm development progresses, which we attribute to the low oxygen levels typical of densely populated bacterial environments. These findings reveal new features of the photokilling mechanism and redefine the approach to designing effective antimicrobial photoinactivation strategies by integrating the key physical characteristics of bacterial biofilms. Significance StatementAwareness of the bacterial worlds global importance is steadily growing in both science and society. Among the critical challenges, the continuing increase in multidrug resistance to antibiotics represents a major public health concern reinforcing the urgency of alternative antimicrobial therapies with photoinactivation as a promising approach. However, its full potential can only be achieved through a better understanding of the involved mechanisms in relevant environments. In this study, we combined experimental and theoretical approaches to investigate the photoinactivation of bacteria within a developing biofilm, the dominant bacterial lifestyle. Our comprehensive analysis sheds light on the mechanisms and limitations of photoinactivation in the fight against microbes, which is essential for designing novel antibacterial phototherapies.

biophysics↗

bioRxiv2022

FLAGELLAR MOTILITY DURING E. COLI BIOFILM FORMATION PROVIDES A COMPETITIVE DISADVANTAGE WHICH RECEDES IN THE PRESENCE OF CO-COLONIZERS.

In nature, bacteria form biofilms in very diverse environments, involving a range of specific properties and exhibiting competitive advantages for surface colonization. However, the underlying mechanisms are difficult to decipher. In particular, the contribution of cell flagellar motility to biofilm formation remains unclear. Here, we examined the ability of motile and nonmotile E. coli cells to form a biofilm in a well-controlled geometry, both in a simple situation involving a single-species biofilm and in the presence of co-colonizers. Using a millifluidic channel, we determined that motile cells have a clear disadvantage in forming a biofilm, exhibiting a long delay as compared to nonmotile cells. By monitoring biofilm development in real time, we observed that the decisive impact of flagellar motility on biofilm formation consists in the alteration of surface access time. Implementing a simple mathematical model to calculate surface access velocity for both motile (diffusion) and nonmotile (settling) cells, we discovered that the competitive advantage strongly depends on the geometry of the environment to be colonized. Interestingly, this advantage reverts for the smallest geometries, with a crossover at a height of 100 m. We also report that the difference between and nonmotile cells in the ability to form a biofilm diminishes in the presence of cocolonizers, which could be due to motility inhibition through the consumption of key resources by the co-colonizers. We conclude that the impact of flagellar motility on surface colonization closely depends on the environment geometry and the population features, suggesting a unifying vision of the role of cell motility in surface colonization and biofilm formation.

microbiology↗