Proteomics characterization of biofilm formation by salt-tolerant Schwannyomyces etchellsii in seawater-based growth medium

Microbial biofilms are complex communities with cells embedded in an extracellular matrix. We previously discovered that salt-tolerant yeasts Debaryomyces fabryi, Schwanniomyces etchellsii, Schwanniomyces polymorphus and Kluyveromyces marxianus were able to form biofilms when grown in seawater- but not in freshwater-based media. The extracellular matrices of these biofilms were composed mainly of carbohydrates and proteins involved in metabolic processes and the response to stimuli. We herein focus on one of these yeasts, S. etchellsii, to explore its molecular determinants for biofilm formation in depth. We describe new analyses in which the proteome of cells in the biofilm network formed in seawater-based media is compared to that of the planktonic cells co-existing with them and with cells suspended in freshwater-based growth media. According to our data, in both cases biofilms cells contain overexpressed proteins involved in protein biosynthesis, in membrane structures and in transport mediated by vesicles. The great number of proteins with higher expression in these cells participating in translation and located in ribosomes indicate that they are more engaged in protein biosynthesis than their counterparts. Analyses carried out with the STRING database reinforced these results. Cell viability was also wider in biofilm cells. Our analyses have also allowed us to detect in S. etchellsii a homolog of the Candida albicans Spf1p. This protein is an ion transporter P-type ATPase in this microorganism, which participates in several processes, including cellular adhesion and cell wall organization and biogenesis. Our work provides a dataset with a large number of unknown proteins of S. etchellsii that show sequence similarity to proteins from other yeasts; this knowledge will help to better understand the proteome of this yeast and to look for future biotechnological applications.