Versatility of the Burkholderia cepacia Complex for the Biosynthesis of Exopolysaccharides: A Comparative Structural Investigation

Abstract

The Burkholderia cepacia Complex assembles at least eighteen closely related species that are ubiquitous in nature. Some isolates show beneficial potential for biocontrol, bioremediation and plant growth promotion. On the contrary, other strains are pathogens for plants and immunocompromised individuals, like cystic fibrosis patients. In these subjects, they can cause respiratory tract infections sometimes characterised by fatal outcome. Most of the Burkholderia cepacia Complex species are mucoid when grown on a mannitol rich medium and they also form biofilms, two related characteristics, since polysaccharides are important component of biofilm matrices. Moreover, polysaccharides contribute to bacterial survival in a hostile environment by inhibiting both neutrophils chemotaxis and antimicrobial peptides activity, and by scavenging reactive oxygen species. The ability of these microorganisms to produce exopolysaccharides with different structures is testified by numerous articles in the literature. However, little is known about the type of polysaccharides produced in biofilms and their relationship with those obtained in non-biofilm conditions. The aim of this study was to define the type of exopolysaccharides produced by nine species of the Burkholderia cepacia Complex. Two isolates were then selected to compare the polysaccharides produced on agar plates with those formed in biofilms developed on cellulose membranes. The investigation was conducted using NMR spectroscopy, high performance size exclusion chromatography, and gas chromatography coupled to mass spectrometry. The results showed that the Complex is capable of producing a variety of exopolysaccharides, most often in mixture, and that the most common exopolysaccharide is always cepacian. In addition, two novel polysaccharide structures were determined: one composed of mannose and rhamnose and another containing galactose and glucuronic acid. Comparison of exopolysaccharides obtained from cultures on agar plates with those extracted from biofilms on cellulose membranes showed important differences, thus suggesting that extrapolating data from non-biofilm conditions might not always be applicable.

A novel rhamno-mannan exopolysaccharide isolated from biofilms of Burkholderia multivorans C1576

“…S5 in Supplementary data) revealed the presence of almost pure cepacian, when the cellulose membrane was used, and of a mixture of cepacian and the rhamnomannan when growth was developed directly on agar, as already found in a preliminary investigation. 23 In the latter case, the anomeric region of the 1 H NMR spectrum revealed resonances clearly belonging to cepacian 4 together with signals at 5.27, 5.24 and 5.04 ppm, attributed to the rhamno-mannan. Two signals were found at 1.30 and 1.24 ppm, the former belonging to rhamnose H-6's of the rhamno-mannan and the latter assigned to the rhamnose in cepacian, further confirming the presence of the two EPOL's.…”

Whole-Genome Sequencing of Three Clonal Clinical Isolates of B. cenocepacia from a Patient with Cystic Fibrosis

“…It is notable that we were unable to detect any genomic differences between the mucoid C3921 isolate and its nonmucoid derivative C3921-CTZ32G. BCC bacteria are known to be capable of producing a number of different exopolysaccharides [ 22 , 25 , 51 – 53 ]. However, the main exopolysaccharide produced in most clinical strains of BCC is ‘cepacian’ which is produced under the control of genes in the bce-I and bce-II loci (annotated on the J2315 genome sequence BCAM0854-BCAM0864 and BCAM1003-1011 respectively) [ 29 ].…”

The Regulator Gene <b><i>rnc</i></b> Is Closely Involved in Biofilm Formation in <b><i>Streptococcus mutans</i></b>

“…Column calibration was performed using various standard dextrans (M w of 1.0 × 10 3 , 3.5 × 10 3 , 1.0 × 10 4 , 1.0 × 10 5 , and 1.0 × 10 6 g/mol; Sigma, San Francisco, CA, USA). The corresponding molecular weights of the samples were calculated using the Agilent GPC software [Cuzzi et al, 2014].…”