An indication for the presence of extracellular DNA (eDNA) was inferred
from the results described above and it was further supported
by fluorescence microscopy with propidiumiodide (PI) that specifically
stains DNA (Fig. 5B). When the mature biofilm produced by strain
WCFS1was treated with either Proteinase K or DNase I, both CV staining
and culturable cell numbers in the biofilm decreased (Fig. 5A). It can be
excluded that the addition of Proteinase K affected the initial attachment
of cells since its addition along with the inoculum did not influence
in the initial attachment up to 2.5 h (data not shown). Similar
effects after Proteinase K and DNase I additionwere observed for strains
FBR 3, FBR 5 and FBR 6 (Fig. 5A). Strains FBR 1 and FBR 2 showed no detectable
level of CV staining, however, the culturable cell numbers in the
biofilm were reduced. Remarkably, the biofilm produced by strain FBR
4, was only reduced after addition of Proteinase K, while DNase I treatment
did not have a significant effect. It cannot be excluded that other
components in the biofilm matrix produced by these strains interfere
with the accessibility of the eDNA. Proteinase K treatment resulted in
a large decrease in attached cells for all the L. plantarum strains resulting
in CV staining below detection level.
An indication for the presence of extracellular DNA (eDNA) was inferredfrom the results described above and it was further supportedby fluorescence microscopy with propidiumiodide (PI) that specificallystains DNA (Fig. 5B). When the mature biofilm produced by strainWCFS1was treated with either Proteinase K or DNase I, both CV stainingand culturable cell numbers in the biofilm decreased (Fig. 5A). It can beexcluded that the addition of Proteinase K affected the initial attachmentof cells since its addition along with the inoculum did not influencein the initial attachment up to 2.5 h (data not shown). Similareffects after Proteinase K and DNase I additionwere observed for strainsFBR 3, FBR 5 and FBR 6 (Fig. 5A). Strains FBR 1 and FBR 2 showed no detectablelevel of CV staining, however, the culturable cell numbers in thebiofilm were reduced. Remarkably, the biofilm produced by strain FBR4, was only reduced after addition of Proteinase K, while DNase I treatmentdid not have a significant effect. It cannot be excluded that othercomponents in the biofilm matrix produced by these strains interferewith the accessibility of the eDNA. Proteinase K treatment resulted ina large decrease in attached cells for all the L. plantarum strains resultingin CV staining below detection level.
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