The biofilm of Burkholderia cenocepacia H111 contains an exopolysaccharide composed of l-rhamnose and l-mannose: Structural characterization and molecular modelling

Microscopy and modelling investigations on the morphology of the biofilm exopolysaccharide produced by Burkholderia multivorans strain C1576

Bacteria form very often biofilms where they embed in a self-synthesized matrix exhibiting a gel-like appearance. Matrices offer several advantages, including defence against external threats and the easiness of intercellular communication. In infections, biofilm formation enhances bacteria resistance against antimicrobials, causing serious clinical problems for patients' treatments. Biofilm matrices are composed of proteins, extracellular DNA, and polysaccharides, the latter being the major responsible for matrix architecture. The repeating unit of the biofilm polysaccharide synthesized by Burkholderia multivorans strain C1576 contains two mannoses and two sequentially linked rhamnoses, one of them 50 % methylated on C-3. Rhamnose, a 6-deoxysugar, has lower polarity than other common monosaccharides and its methylation further reduces polarity. This suggests a possible role of this polysaccharide in the biofilm matrix; in fact, computer modelling and atomic force microscopy studies evidenced intra- and inter-molecular non-polar interactions both within polysaccharides and with aliphatic molecules. In this paper, the polysaccharide three-dimensional morphology was investigated using atomic force microscopy in both solid and solution states. Independent evidence of the polymer conformation was obtained by transmission electron microscopy which confirmed the formation of globular compact structures. Finally, data from computer dynamic simulations were used to model the three-dimensional structure.

Structure characterization of novel heteropolysaccharides from Pteridium revolutum with antioxidant and antiglycated activities

This study aims to analysis the structures of polysaccharides isolated from Pteridium revolutum and their antioxidant and antiglycated activities. Three novel water-soluble heteropolysaccharides, named PRP0, PRP1, and PRP2, were isolated from P. revolutum. The average molecular weight was determined by high performance gel permeation chromatography analysis as 1.04 × 106, 8.39 × 105, and 7.37 × 105 Da, respectively. Their structures were characterized using physicochemical and spectroscopic methods. The antioxidant and antiglycated activities were assayed in vitro. PRP0, PRP1, and PRP2 consist of l-Ara, l-Rha, d-Man, d-Xyl, d-Fuc, d-Gal, and d-Glc in different proportions. PRP1 mainly has a backbone of (1 → 3,6)-linked d-Man and (1 → 3)-linked d-Gal on main chain. PRP2 is mainly composed of (1 → 2,4)-linked d-Man and (1 → 3)-linked d-Gal on main chain. All polysaccharides have strong scavenging power on 2,2-difenil-1-picril-hidrazil and hydroxyl radicals and significantly antiglycated activity in Bovine serum albumin-Glucose model, which showing that the polysaccharides have potential application value on the functional food.

The Bep gene cluster in Burkholderia cenocepacia H111 codes for a water-insoluble exopolysaccharide essential for biofilm formation

Burkholderia cenocepacia is an opportunistic pathogen isolated from cystic fibrosis patients where it causes infections that are extremely difficult to treat with antibiotics, and sometimes have a fatal outcome. Biofilm is a virulence trait of B. cenocepacia, and is associated with infection persistence and increased tolerance to antibiotics. In biofilms exopolysaccharides have an important role, conferring mechanical stability and antibiotic tolerance. Two different exopolysaccharides were isolated from B. cenocepacia H111 biofilms: a water-soluble polysaccharide rich in rhamnose and containing an L-Man residue, and a water-insoluble polymer made of glucose, galactose and mannose. In the present work, the product encoded by B. cenocepacia H111 bepA-L gene cluster was identified as the water-insoluble exopolysaccharide, using mutant strains and NMR spectroscopy of the purified polysaccharides. It was also demonstrated that the B. cenocepacia H111 wild type strain produces the water-insoluble exopolysaccharide in pellicles, thus underlining its potential importance in in vivo infections.

Structure characterization, antioxidant capacity, rheological characteristics and expression of biosynthetic genes of exopolysaccharides produced by Lactococcus lactis subsp. lactis IMAU11823

Exopolysaccharides (EPSs) from lactic acid bacteria have special functions and complex structures, but the function and structure of EPSs of the important dairy starter, Lactococcus (L.) lactis subsp. lactis, are less known. This study investigated the cytotoxicity, antioxidant capacities, rheological characteristics, chemical structure and expression of biosynthetic genes of EPSs of the L. lactis subsp. lactis IMAU11823. The EPSs showed strong reducing power and no cytotoxicity. EPS-1 comprised glucose and mannose (molar ratio of 7.01: 1.00) and molecular weight was 6.10 × 10⁵ Da, while EPS-2 comprised mannose, glucose and rhamnose (7.45: 1.00: 2.34) and molecular weight was 2.93 × 10⁵ Da. EPS-1 was a linear structure comprised two sugar residues, while EPS-2 was more complex, non-linear, and comprised eight sugar residues. In additions, our study proposed an EPS biosynthesis model for the IMAU11823 strain. The current findings have broadened the understanding of the formation, structure and function of complex EPSs of IMAU11823.

Human Cryptic Host Defence Peptide GVF27 Exhibits Anti-Infective Properties against Biofilm Forming Members of the Burkholderia cepacia Complex

Therapeutic solutions to counter Burkholderia cepacia complex (Bcc) bacteria are challenging due to their intrinsically high level of antibiotic resistance. Bcc organisms display a variety of potential virulence factors, have a distinct lipopolysaccharide naturally implicated in antimicrobial resistance. and are able to form biofilms, which may further protect them from both host defence peptides (HDPs) and antibiotics. Here, we report the promising anti-biofilm and immunomodulatory activities of human HDP GVF27 on two of the most clinically relevant Bcc members, Burkholderia multivorans and Burkholderia cenocepacia. The effects of synthetic and labelled GVF27 were tested on B. cenocepacia and B. multivorans biofilms, at three different stages of formation, by confocal laser scanning microscopy (CLSM). Assays on bacterial cultures and on human monocytes challenged with B. cenocepacia LPS were also performed. GVF27 exerts, at different stages of formation, anti-biofilm effects towards both Bcc strains, a significant propensity to function in combination with ciprofloxacin, a relevant affinity for LPSs isolated from B. cenocepacia as well as a good propensity to mitigate the release of pro-inflammatory cytokines in human cells pre-treated with the same endotoxin. Overall, all these findings contribute to the elucidation of the main features that a good therapeutic agent directed against these extremely leathery biofilm-forming bacteria should possess.