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.