Interestingly, not a single surface-associated protein was identified as PD98059 mw being solely expressed in sessile or planktonic cells. Nineteen proteins were significantly overexpressed in C. albicans
biofilms grown in 24-well microtiter plates, compared with planktonic cultures, and in contrast to the results obtained by Thomas et al. (2006), ENO1 was twofold underexpressed. Highly significant overexpression was observed for citrate synthase (14.45-fold), and several proteins involved in oxidative stress, including alkyl hydroperoxide reductase AHP1 and several other reductases (GRP2, MCR1, TSA1, PST1 and TRX1), were also overexpressed. Proteomics has also been used for a three-way comparison of planktonic yeast cells, planktonic hyphae and sessile cells (Martinez-Gomariz PI3K Inhibitor Library manufacturer et al., 2009). One hundred and seventy-five cytoplasmic and 70 cell surface-associated proteins were differentially expressed between sessile and planktonic yeast cells, while these numbers were 218 and 51, respectively, when sessile cells were compared with planktonic hyphae. The fold over- or underexpression varied considerably depending on the comparison
made. For example, MET15 was downregulated in biofilms when compared with planktonic yeast cells, but upregulated when biofilms were compared with planktonic hyphae, confirming that morphology is an important factor. Further complicating the comparison of protein expression is the presence of various isoforms of the same protein. For example six
isoforms of pyruvate decarboxylase were identified by Martinez-Gomariz and colleagues: isoforms 1, 2, 5 and 6 are underexpressed in biofilms compared with planktonic yeast cells, while isoforms 3 and 4 are overexpressed. A detailed analysis of the results obtained in the studies summarized PTK6 above reveals that, although generally representatives of particular classes of genes are differentially expressed between planktonic and sessile cells (Fig. 1), there is very little overlap between C. albicans genes identified as differentially expressed in different studies and the same is true for other microorganisms. The observation that the experimental conditions for culturing the cells before RNA extraction are often variable (Table 1) offers a first explanation. There are a wide range of biofilm model systems available, and few studies have used the same model system. Similarly, planktonic cells are cultured in a variety of ways (Table 1).