Abstract
Biofilms are aggregates of microbial cells encased in a highly hydrated matrix made up of self-produced extracellular polymeric substances (EPS) which consist of polysaccharides, proteins, nucleic acids, and lipids. While biofilm matrix polysaccharides are unraveled, there is still poor knowledge about the identity and function of matrix-associated proteins. With this work, we performed a comprehensive proteomic approach to disclose the identity of proteins associated with the matrix of biofilm-growing Burkholderia multivorans C1576 reference strain, a cystic fibrosis clinical isolate. Transmission electron microscopy showed that B. multivorans C1576 also releases outer membrane vesicles (OMVs) in the biofilm matrix, as already demonstrated for other Gram-negative species. The proteomic analysis revealed that cytoplasmic and membrane-bound proteins are widely represented in the matrix, while OMVs are highly enriched in outer membrane proteins and siderophores. Our data suggest that cell lysis and OMVs production are the most important sources of proteins for the B. multivorans C1576 biofilm matrix. Of note, some of the identified proteins are lytic enzymes, siderophores, and proteins involved in reactive oxygen species (ROS) scavenging. These proteins might help B. multivorans C1576 in host tissue invasion and defense towards immune system assaults.
Highlights
In natural settings and in man-made environments, many bacteria are generally found to live in highly complex communities referred to as biofilms, which are surface-associated aggregates of microbial cells embedded in a matrix consisting of extracellular polymeric substances (EPS) [1,2,3,4]
B. multivorans C1576 (LMG 16660), a reference strain that belongs to the panel of B. cepacia complex strains (EP1), was purchased from the BCCMTM bacteria collection
An overnight liquid culture of B. multivorans C1576 grown in MH medium was diluted to obtain a cell suspension having 0.13 OD at 600 nm, three aliquots of 10 μL of the cell dilution were transferred on the membranes deposited on the Petri dishes, and they were incubated at 30 ◦C for 7 days
Summary
In natural settings and in man-made environments, many bacteria are generally found to live in highly complex communities referred to as biofilms, which are surface-associated aggregates of microbial cells embedded in a matrix consisting of extracellular polymeric substances (EPS) [1,2,3,4]. The composition of the biofilm matrix varies with the bacterial species and the growth conditions under which biofilms develop, EPS generally include polysaccharides, proteins, nucleic acids, and lipids [5]. The composition of the biofilm matrix consists of exopolysaccharides, proteins, and nucleic acids, the components and their proportions are dependent on the microorganism and the conditions of their growth [5]. Matrix-associated proteins are represented by membrane surface adhesins, proteins building up extracellular appendages (flagella, pili, and fimbriae), proteins actively secreted, and proteins transported by outer membrane vesicles (OMVs) [5]
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