Abstract
Most microbes can produce surface-associated or suspended aggregates called biofilms, which are encased within a biopolymer-rich matrix. The biofilm matrix provides structural integrity to the aggregates and shields the resident cells against environmental stressors, including antibiotic treatment. Microscopy permits examination of biofilm structure in relation to the spatial localization of important biofilm matrix components. This review highlights microscopic approaches to investigate bacterial biofilm assembly, matrix composition, and localization using Pseudomonas aeruginosa as a model organism. Initial microscopic investigations provided information about the role key matrix components play in elaborating biofilm aggregate structures. Additionally, staining of matrix components using specific labels revealed distinct positioning of matrix components within the aggregates relative to the resident cells. In some cases, it was found that individual matrix components co-localize within aggregates. The methodologies for studying the biofilm matrix are continuing to develop as our studies reveal novel aspects of its composition and function. We additionally describe some outstanding questions and how microscopy might be used to identify the functional aspects of biofilm matrix components.
Highlights
Microbes form multicellular communities called biofilms (Costerton et al, 1995)
P. aeruginosa biofilms were cultured in flow-cells and the resulting biomass was stained with Syto9 and imaged by Confocal laser scanning microscopy (CLSM)
Crude preparations of Pel were often contaminated with extracellular DNA (eDNA). These results suggested that Pel and eDNA may interact to provide structure to P. aeruginosa biofilms
Summary
Microbes form multicellular communities called biofilms (Costerton et al, 1995). Within these communities, microbial aggregates are encased in a biopolymer-rich extracellular matrix. The amount of adherent biomass for the Δpsl mutant was much less than the parental strain, it formed small aggregates, suggesting that Pel may play more of role in the biofilm formation of this strain than was recognized based upon the static biofilm results alone In this way, microscopy was a useful tool to understand differing biofilm matrix requirements of different isolates. This study provided information about the ability of isolates to use either Psl or Pel to form adherent biomass, and highlighted that each of these EPS can play distinct roles in structuring biofilm aggregates These results illustrate that knowing the predominant matrix EPS is not a good predictor of biofilm structure. As described of this review, CLSM of flow-cell biofilms has been used to provide mechanistic understanding of how the matrix interactions and biofilm localizations of Psl and Pel result in their overlapping and unique biofilm roles
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