The Extracellular Vesicles Containing Inorganic Polyphosphate of Candida Yeast upon Growth on Hexadecane

Abstract

The cell wall of Candida yeast grown on presence of hexadecane as a sole carbon source undergoes structural and functional changes including the formation of specific supramolecular complexes—canals. The canals contain specific polysaccharides and enzymes that provide primary oxidization of alkanes. In addition, inorganic polyphosphate (polyP) was identified in Candida maltosa canals. The aim of the work was a comparative study of the features of cell walls and extracellular structures in yeast C. maltosa, C. albicans and C. tropicalis with special attention to inorganic polyphosphates as possible part of these structures when grown on the widely used xenobiotic hexadecane (diesel fuel). Fluorescence microscopy with DAPI has shown an unusual localization of polyP on the cell surface and in the exovesicles in the three yeast species, when growing on hexadecane. Electron-scanning microscopy showed that the exovesicles were associated with the cell wall and also presented in the external environment probably as biofilm components. Treatment of hexadecane-grown cells with purified Ppx1 polyphosphatase led to the release of phosphate into the incubation medium and the disappearance of polyP in vesicles and cell wall observed using microscopic methods. The results indicate the important role of polyP in the formation of extracellular structures in the Candida yeast when consuming hexadecane and are important for the design of xenobiotic destructors based on yeast or mixed cultures.

Importance of Non-Covalent Interactions in Yeast Cell Wall Molecular Organization

“…Another example is the likely involvement of polyphosphates in the formation of extracellular vesicles in the Candida yeast consuming hexadecane. The yeasts C. maltosa , C. albicans and C. tropicalis form extracellular vesicles when grown on hexadecane as the sole carbon source [ 102 ]. Electron-scanning microscopy showed that these vesicles were associated with the cell wall and may be biofilm components.…”

“…The presence of polyP in these vesicles was demonstrated by fluorescence microscopy with DAPI, a fluorochrome which shows orange fluorescence with these polymers. The treatment of hexadecane-grown cells with yeast Ppx1 polyphosphatase led to the degradation of vesicles, observed by scanning and fluorescence microscopy, and the release of orthophosphate into the medium [ 102 ]. These results indicate the important role of polyP in the formation of extracellular vesicles in the Candida yeast consuming hexadecane.…”

“…The cell wall of hexadecane-grown C. maltosa fluoresces more intensively with DAPI than that of glucose-grown cells. This fluorescence disappeared after a treatment with polyphosphatase Ppx1 [ 102 ]. The presence of polyP in the cell wall of the pathogenic yeast Cryptococcus neoformans was demonstrated by combining fluorescence microscopy, biochemical extraction, scanning electron microscopy, electron probe X-ray microanalysis and the 3D reconstruction of high-pressure-frozen and freeze-substituted cells by focused ion beam-scanning electron microscopy [ 137 ].…”