Revealing the secret life of natural and artificial biofilms

Dr. Anne Kammel & Prof. Peter Schierack, Brandenburg University of Technology Cottbus - Senftenberg, Germany

Bacterial biofilms are multidimensional communities consisting of sessile bacterial cells that live in a self-produced matrix of extracellular polymeric substances (EPS) containing exopolysaccharides, proteins and DNA adhered to abiotic or biotic surface. These consortia are widespread in nature and provide an important survival strategy for the embedded bacteria towards harsh environmental conditions, such as antimicrobials and host defense mechanisms. Biofilms can develop on almost any surface and could have beneficial as well as very harmful effects. Here we describe two different undesired harmful effects caused by the natural formation of biofilms.

(1) In sewers, the reduced amount of wastewater results in an increased service life of the wastewater with the same organic content. These conditions favour the formation of biofilms in the sewers. The biochemical conversion of sulfate via hydrogen sulfide to sulfuric acid leads to biogenic (sulfuric acid) corrosion of the concrete and a considerable odor nuisance. Surveys of sewer operators have shown that the reduction of biogenic corrosion and the associated odour nuisance are among the most urgent problems in the operation of wastewater disposal systems. Biogenic corrosion is caused by the interaction of sulfur-reducing and sulfur-oxidizing bacteria. The sulfur reducing bacteria (SRB), which are located in the aqueous phase at the bottom of the sewer, reduce elemental sulfur to hydrogen sulfide under anaerobic conditions. Sulfur-oxidizing bacteria, which are located at the apex of the sewer pipe, use the hydrogen sulfide from the sewer atmosphere for aerobic respiration. The resulting sulfuric acid causes the corrosion of the concrete pipe leading to the destruction of the sewer pipe systems.

(2) In medicine, biofilms are a decisive factor of morbidity, mortality and higher costs. Information from the National Institutes of Health indicate that up to 80% of human bacterial infections involve biofilm‐associated microorganisms. Microbial communities are found in infections such as chronic otitis media, periodontitis, chronic wounds, recurrent urinary tract infections or endocarditis. Biofilm formation is also prevalent on medical devices such as catheters, stents, orthopedic implants, contact lenses and implantable electronic devices, leading to nosocomial and chronic infections. Although materials science and technology have made great progress in the field of implantable biomaterials, infection still poses a major risk to any medical device planted in the body. In general, any implanted foreign material is susceptible to microbial colonization. The search for new materials and coatings with lower colonization potential and antibacterial activity is of great importance to reduce biofilm formation.

However, there is no standardized procedure to examine the colonization characteristics of bacteria in the biofilm state in situ.

To identify the bacterial composition and architecture of the formed biofilms we combine genotyping (e.g. next-generation sequencing) and phenotyping methods (an automated epifluorescence microscopy system).The analysis of the 16S rRNA metagenome by means of next generation sequencing (NGS) allows us to identify the microorganisms (genus/species) independent of their cultivability. Further characterization of the three-dimensional biofilm is performed with our proprietary imaging platform technology VideoScan, which is a versatile, fully automated fluorescence microscopy platform. The platform provides information about the number of bacteria, the colonized area as well as the maximum of the biofilm. This novel method enables the standardized, automated investigation of the colonization with bacteria on different materials. Using fluorescence-labeled DNA probes (Fluorescence In-Situ Hybridization, FISH) we can specifically identify bacteria by their genus in mixed biofilms and, in combination with other dyes such as Calcoflour and fluorescence-labeled lectins, characterize the components of extracellular polymeric substances essential for bacterial agglomerates.

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