Targeted disruption of the extracellular polymeric network of Pseudomonas aeruginosa biofilms by alginate oligosaccharides

Acquisition of a mucoid phenotype by Pseudomonas sp. in the lungs of cystic fibrosis (CF) patients, with subsequent over-production of extracellular polymeric substance (EPS), plays an important role in mediating the persistence of multi-drug resistant (MDR) infections. The ability of a low molecular weight (Mn=3200 g mol-1) alginate oligomer (OligoG CF-5/20) to modify biofilm structure of mucoid Pseudomonas aeruginosa (NH57388A) was studied in vitro using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) with Texas Red (TxRd®)-labelled OligoG and EPS histochemical staining. Structural changes in treated biofilms were quantified using COMSTAT image-analysis software of CLSM z-stack images, and nanoparticle diffusion. Interactions between the oligomers, Ca2+ and DNA were studied using molecular dynamics simulations (MDS), Fourier transform infrared spectroscopy (FTIR) and isothermal titration calorimetry (ITC). Imaging demonstrated that OligoG treatment (>0.5%) inhibited biofilm formation, demonstrating a significant reduction in both biomass and biofilm height (17.8 vs. 5.5 µm; P <0.05). TxRd®-labelled oligomers readily diffused into established (24 h) biofilms. OligoG treatment (≥2%) induced alterations in the EPS of established biofilms; significantly reducing the structural quantities of sugar residues, and extracellular (e)DNA (P <0.05) with a corresponding increase in nanoparticle diffusion (P<0.05) and antibiotic efficacy against established biofilms. ITC demonstrated an absence of rapid complex formation between DNA and OligoG and confirmed the interactions of OligoG with Ca2+ evident in FTIR and MDS. The ability of OligoG to diffuse into biofilms, potentiate antibiotic activity, disrupt DNA-Ca2+-DNA bridges and biofilm EPS matrix highlights its potential for the treatment of biofilm-related infections

Five tests of food-limited growth of larvae in coastal waters by comparisons of rates of development and form of echinoplutei

International audienceAny single method of testing food limitation can be misleading or inconclusive. We therefore used five different tests for food-limited growth of larvae of a sea urchin from the northwest Mediterranean: 1. In both spring and autumn, larvae given a nearly natural ration of food from daily changes of seawater grew and developed more slowly than larvae with the same water enhanced with a cultured alga. 2. Larvae given a nearly natural ration of food developed more slowly in autumn, when concentrations of chlorophyll a and particles in the plankton were lower, than in spring when these indications of food were higher. 3. Larvae given the enhanced ration grew and developed more rapidly than larvae in presumed cohorts in the plankton. 4. In both spring and autumn, larvae in the field had a food-limited form (longer arms and delayed formation of the echinus rudiment) in contrast to larvae given an enhanced ration. 5. Larvae in the autumn plankton had a more food-limited form than larvae in the spring plankton. Results of all five tests indicated food-limited growth in coastal waters in autumn; three indicated food-limited growth in spring. The concentrations of natural food were not unusually low. Food-limited growth suggests that these larvae may commonly feed with maximal or near-maximal clearance rates. If echinoid larval growth is limited by food under these conditions, it is likely that growth of other larval invertebrates is food limited in many coastal waters