No abstract

Nutrient-transporting channels are found throughout mature Escherichia coli biofilms, however the influence of environmental conditions on intra-colony channel formation is poorly understood. We report the effect of different substrate nutrient concentrations and agar stiffness on the structure and distribution of intra-colony channels in mature E. coli colony biofilms using fluorescence mesoscopy and quantitative image analysis. Intra-colony channel width was observed to increase non-linearly with radial distance from the centre of the biofilm and channels were, on average, 50% wider at the centre of carbon-limited biofilms compared to nitrogen-limited biofilms. Channel density also differed in colonies grown on rich and minimal medium substrates, with the former creating a network of tightly packed channels and the latter leading to well-separated, wider channels with easily identifiable edges. We conclude that intra-colony channel morphology in E. coli biofilms is influenced by both substrate composition and nutrient availability.

No abstract

The morphology of bacterial colonies depends on nutrient availability. We use the Mesolens, which can image a 100 mm 3 volume with subcellular resolution throughout, to investigate the internal structure of colonies grown on agar substrates with different glucose and ammonia concentrations. We observe intracolony channels in both nutrient-deprived and nutrient rich colonies, with channel widths dependent on the nutrient availability.

We provide a brief review of the development and application of the Mesolens and its impact on microbiology. Microbial specimens such as infected tissue samples, colonies surfaces, and biofilms are routinely collected at the mesoscale. This means that they are relatively large multimillimetre-sized samples which contain microscopic detail that must be observed to answer important questions across various sectors. The Mesolens presents the ideal imaging method to study these specimens as no other optical microscope can thanks to its unique combination of low magnification and high numerical aperture providing large field-of-view, high-resolution imaging. We demonstrate the current applications of the Mesolens to microbial imaging and go on to outline the huge potential of the Mesolens to impact other key areas of microbiology. K E Y W O R D Sbiofilm, high-content imaging, mesoscopic imaging, microbiology From Louis Pasteur's disproof of spontaneous generation to Robert Koch's germ theory, our understanding of microorganisms has crucially depended on optical microscopy. Microscopes, essentially like those used by Pasteur and Koch, are still indispensable today as a complement to biochemical and molecular methods in the diagnosis of infection.However, despite its widespread application in microbiology, the optical microscope has not changed in basic design for over 100 years. The ratio of magnification to numerical aperture (NA) has been set to a fixed value of approximately 40:1 for all microscope objectives. The reason for this is wholly historical: this proportion gives an image in which the detail is suited to the capacity of the human eye. 1 In microbiology, a 4× NA 0.