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In-Depth Information
Proteins and Functions Differentially Regulated by P. gingivalis in a
Community
Cell Envelope and Cell Structure
In bacterial communities significant surface-surface contact occurs both within and
among accumulations of the constituent species, as was also observed in the P. gingi-
valis-F. nucleatum-S. gordonii consortia. Regulation of outer membrane constituents
of P. gingivalis would thus be predicted in the context of a community and this was
borne out by the proteomic results. Overall, 84 proteins annotated as involved in the
cell envelope were detected, and 40 of these showed reduced abundance in the three
species community, indicating an extensive change to the cell envelope. Only four
proteins showed increased abundance, two OmpH proteins (PGN0300, PGN0301) and
two lipoproteins (PGN1037, PGN1998). The MreB (PGN0234), a bacterial actin ho-
mologue that plays a role in determining cell shape, showed almost a 2-fold decrease
in community derived P. gingivalis . Expression of MreB has been found to decrease
under stress or during stationary phase in Vibrio paraheamolyticus [35]. However,
stress-related proteins were generally reduced in P. gingivalis cells in the community
(see below) so stress is an unlikely explanation for the change in MreB. Rather, the
decrease in MreB abundance may be due to the P. gingivalis cells entering a state re-
sembling stationary phase or responding in a previously unseen way to the formation
of the three species community.
Protein Synthesis
Extensive changes were observed in ribosomal proteins and in translation elongation
and initiation proteins. While overall more proteins showed reduced abundance in
the three species community, the changes to the translational machinery were almost
exclusively increases in abundance. Of 49 ribosomal proteins detected, 27 showed
increased abundance, while only one showed decreased abundance. Of nine transla-
tion elongation and initiation proteins detected, none showed significant abundance
decreases but five showed increased abundance (EfG (PGN1870), putative EfG
(PGN1014), EfTs (PGN1587), EfTu (PGN1578), and If2 (PGN0255)). This represents
not only a substantial portion of the translational machinery but also a large portion,
36%, of the proteins showing increased abundance. It is well known that ribosomal
content is generally proportional to growth rate [36]; however, given that the cells
were not in culture medium during the assay, rapid growth is an unlikely explana-
tion for these results. The increased ribosomal content presumably indicates increased
translation, consistent with the community providing physiologic support to P. gingi-
valis and allowing higher levels of protein synthesis.
Vitamin Synthesis
Pathways for synthesizing several vitamins showed reduced protein abundance in the
three species community. Most of the proteins involved in thiamine diphosphate (vita-
min B1) biosynthesis were down-regulated (Figure 4). Thiamine is a cofactor for the
2-oxoglutarate dehydrogenase complex that converts 2-oxoglutarate to succinyl-CoA
and for the transketolase reactions of the anaerobic pentose phosphate pathway [37].
However, transketolase (PGN1689, Tkt) showed no abundance change while of the
 
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