Protein expression by planktonic and biofilm cells of Streptococcus mutans

Streptococcus mutans. a major causal agent or dental caries, functions in n ature as a component of a biofilm on teeth (dental plaque) and yet very lit tle information is available on the physiology of the organism in such surf ace-associated communities. As a consequence, we undertook to examine the s ynthesis of proteins by planktonic and biofilm cells growing in a biofilm c hemostat at pH 7.5 at a dilution rate or 0.1 h(-1) (mean generation time = 7 h). Cells were incubated with C-14-labelled amino acids, the proteins ext racted and separated by two-dimensional electrophoresis followed by autorad iography and computer-assisted image analysis. Of 694 proteins analysed, 57 proteins were enhanced 1.3-fold or greater in biofilm cells compared to pl anktonic cells with 13 only expressed in sessile cells. Diminished protein expression was observed with 78 proteins, nine of which were not expressed in biofilm cells. The identification of enhanced and diminished proteins by mass spectrometry and computer-assisted protein sequence analysis revealed that, in general, glycolytic enzymes involved in acid formation were repre ssed in biofilm, cells, while biosynthetic processes were enhanced. The res ults show that biofilm, cells possess novel proteins. of as yet unknown fun ction, that are not present in planktonic cells. (C) 2001 Published by Else vier Science B.V. on behalf of the Federation of European Microbiological S ocieties.