Macromolecular composition of unsaturated Pseudomonas aeruginosa biofilms with time and carbon source

Abstract

Bacteria in nature grow mostly as biofilms, surface-associated cells enveloped by hydrated extracellular polymeric substances (EPS) of bacterial origin. The composite of EPS and biofilm cells is measured when quantifying bacterial biomass from natural samples. However, little is known regarding the relative magnitude of the EPS and cellular fractions of biofilm biomass, particularly in unsaturated systems such as soil and food surfaces. In this study, we examined the cellular and extracellular fractions of Pseudomonas aeruginosa biofilms for DNA, protein and carbohydrate content. Biofilms were cultured in a model laboratory system that simulates the nutrient gradients and poorly mixed nature of unsaturated systems. We found that unsaturated biofilms exhibited two growth phases – an initial rapid phase and a second phase of slower or negligible development. However, no lag phase was observed for either carbon source. Cellular DNA accumulated linearly with biomass whereas cellular protein and carbohydrates accumulated exponentially with biomass. High levels of carbohydrate, protein and DNA were observed in the EPS of all samples, representing as much as 50% of these macromolecules in the biofilm. Most EPS accumulated during the second phase of growth, when cellular DNA increased only slightly. However, for biofilms cultured on a poorly bioavailable carbon source, EPS DNA decreased during the second phase, suggesting that EPS may affect bacterial survival under nutrient-limited conditions. Whether a product of overflow metabolism or cell lysis, EPS is a significant component of unsaturated biofilm biomass that probably impacts on bacterial ecology.

Combining biofilm matrix measurements with biomass and viability assays in susceptibility assessments of antimicrobials against Staphylococcus aureus biofilms

“…In addition, their functional roles in the EPS layer can differ. 21 Thus, as for the dimethyl methylene blue method, the application of the WGA assay depends on the presence of PNAG in mature biofilms of the bacterial strains and the interpretation of the data should also take into account the importance of the PNAG component in the matrix. Subsequently, with these three assays, a typical susceptibility study involving three model compounds: penicillin and ciprofloxacin as active antibiotics and the weak antibiotic substance rosmarinic acid as negative control was conducted.…”

Self-organization of bacterial biofilms is facilitated by extracellular DNA

“…As biofilms of P. aeruginosa contain large quantities of eDNA (26)(27)(28)(29)(30) and the tfp of P. aeruginosa have been shown to bind DNA (31), we explored the possibility that eDNA may also contribute to the twitching motility-mediated biofilm expansion. We have found that incorporation of the eDNA degrading enzyme DNaseI into the nutrient media significantly decreased twitching-mediated expansion of P. aeruginosa colony biofilms by 76% (SI Results, Fig.…”

Microbial extracellular polymeric substances: central elements in heavy metal bioremediation

“…Continuous cultivation of the strain PS88 under aerobic condition in the dark led to a high production of exocellular RNA which attained a concentration of 460 mg / L of the medium [52]. Production of extracellular DNA (eDNA) as a component of EPS has been proved to be essential for saturated biofi lm stability during the early stages of biofi lm growth [53].while, the unsaturated biofi lm of Pseudomonas aeruginosa, Pseudomonas putida, Rhodococcus erythropolis and Vivrio paradoxus contained eDNA along with polysaccharides and protein when grown as either single-or dual-species [54,55]. Epifl uorescence and electron microscopy revealed a stable fi lamentous network of eDNA closely bound to the cell surface of environmental bacterial isolates indicating a new function of extracellular DNA, possibly as a structural component.…”