In nature, bacteria often occur in the form of biofilms. In this form they are more resistant and can survive stress factors. The extracellular matrix is crucial for the development of a mature bacterial biofilm. It contains extracellular polymeric substances such as proteins, polysaccharides, and eDNA. In our study, we isolated the EPS layer of four strains of lactic acid bacteria and Pseudomonas fragi ATCC 4973 by centrifugation and compared their composition. We used several different methods to quantify and detect the presence of proteins, polysaccharides and eDNA. The most noticeable differences between the isolates were found in their protein and eDNA content. There were some discrepancies between the methods used to analyse protein content. We concluded that the highest protein levels were present in the isolates of Pseudomonas fragi ATCC 4973. These isolates also contained high molecular weight DNA, whereas the isolates from lactic acid bacteria had only smaller DNA fragments. NMR analysis indicated that the isolate from Pseudomonas fragi ATCC 4973 contained the highest amount of sugars. Despite the differences between methods, our results suggest that the composition of the EPS layer of Pseudomonas fragi differs from that of lactic acid bacteria. Further studies are needed to confirm differences between the composition of the EPS layer of lactic acid bacteria and Pseudomonas fragi and role of the EPS layer compounds in biofilm formation.
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