Fractal complexity of Escherichia coli nutrient transport channels is influenced by cell shape and growth environment

Abstract

Recent mesoscopic characterisation of nutrient-transporting channels inE. colihas allowed the identification and measurement of individual channels in whole mature biofilms. However, their complexity under different physiological and environmental conditions remains unknown. Analysis of confocal micrographs of biofilms formed by cell shape mutants ofE. colishows that channels have a high fractal complexity, regardless of cell phenotype or growth medium. In particular, biofilms formed by the mutant strain ΔompR, which has a wide-cell phenotype, have a higher fractal dimension when grown on rich medium than when grown on minimal medium, with channel complexity affected by glucose and agar concentration in the medium. Osmotic stress leads to a dramatic reduction in ΔompRcell size, but has a limited effect on channel morphology. This work shows that fractal image analysis is a powerful tool to quantify the effect of phenotypic mutations and growth environment on the morphological complexity of internalE. colibiofilm structures. If applied to a wider range of mutant strains, this approach could help elucidate the genetic determinants of channel formation inE. colibiofilms.

Oxygen Microenvironments inE. coliBiofilm Nutrient Transport Channels: Insights from Complementary Sensing Approaches

“…Figure 4 shows a maximum-intensity projection of a biofilm expressing a fluorescent Pcco2::gfp oxygen reporter that conditionally expresses gfp under anoxic conditions with high fidelity. These data show an anoxic core accompanied by diffuse fluorescence emission along the transport channel networks with the highest intensity at the centre of the biofilm and a gradual decrease towards the leading edge, interspersed with anoxic subpopulations matching the spatial pattern of canonical biofilm transport channels reported elsewhere 1,3,4,9 . The spatial overview of oxygen gradients from these data concurs with the nanosensing and electrochemical profiling data, which show a change in oxygen gradients along the channel structures and similarities between the microenvironments of the channels and interstitial cell populations, respectively.…”

“…Key resource trafficking by biofilm transport channels has been well documented in recent literature 1,3,4,18 , but it remained unclear if these seemingly devoid structures were either hypaethral or enclosed and, thereby, the chemical microenvironment was unknown. The channel structures we discuss here were originally hypothesised to be open chasms spreading along the radii of macrocolony biofilms due to their appearance as dark voids during optical imaging experiments.…”

“…These nutrient transport channels were discovered using novel mesoscopic imaging methods 2 . They were found to form according to their local environmental conditions 3 as an emergent property governed by cell shape and driven by cell-to-cell and cell-surface interactions 4 . The proven ability of these channels to translocate nutrients and small particles within mature macrocolony biofilms presents a timely opportunity to develop exploitative channel-mediated bioremediation strategies to lower the impact of biofilms on public health and industry.…”