Info

695 (88.1%)

*Spots displaying statistically different protein quantities in organisms recovered from X cultures compared to Y cultures fulfilled the following criteria: /¡-values of < 0.05 (¿-test); fold change > 2; average volume > 20 (n = 3).

aIncubation conditions X and Y were compared.

b+, overproduced in X; - underproduced in X ; =, no difference

Abbr: CB18, attachment to clay beads for 18 h; CB48, attachment to clay beads for 48 h; F18, control free-cell cultures incubated for 18 h; F48, control free-cell cultures incubated for 48 h.

*Spots displaying statistically different protein quantities in organisms recovered from X cultures compared to Y cultures fulfilled the following criteria: /¡-values of < 0.05 (¿-test); fold change > 2; average volume > 20 (n = 3).

aIncubation conditions X and Y were compared.

b+, overproduced in X; - underproduced in X ; =, no difference

Abbr: CB18, attachment to clay beads for 18 h; CB48, attachment to clay beads for 48 h; F18, control free-cell cultures incubated for 18 h; F48, control free-cell cultures incubated for 48 h.

tance of sessile cells to environmental stresses (8). The third one is composed of membrane proteins. Membrane proteins have been reported to have a substantial influence on attachment and may also play a role in early biofilm development (9,10). They are implied in multidrug resistance pumps of gram-negative bacteria (11,12) and their over/underproduction by ICs may therefore be implied in IC resistance to antibiotics. The expression level of some proteins involved in DNA transcription and translation was also affected by immobilization. So, many cellular functions were altered by the sessile mode of growth, which confirms a number of literature data (13-16). In addition, the biofilm mode of growth also affected a great number of proteins with an unknown function.

8. Here, most identified proteins, whatever their function, were underproduced by biofilm cells compared to control, suspended counterparts. However, no clear expression tendency of proteins whose level was affected in sessile bacteria could be discerned when extending the proteomic analyses to other immobilized-cell systems, either natural (biofilm formation on glass wool fibres) or artificial (entrapment in agar gel layer) (17). Furthermore, the discrimination between trivial and key peptides (i.e., those whose variations in expression level will exert deciding influence on the physiology of immobilized cells) among those differentially expressed by sessile bacteria as compared to free counterparts seems a difficult challenge. It may also be difficult (and sometimes dangerous) to advance a specific role for a given over/underexpressed protein in the biofilm phe-notype.

9. In conclusion, the emergence of proteomics as a powerful tool to compare the global regulation patterns of gene expression in free and immobilized microbial cells opens promising avenues to the study of immobilized cell physiology. The

Table 2

Identification and Function of Proteins Underproduced or Overproduced in Biofilm Cells Compared to Suspended Counterparts

Table 2

Function

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