Soft X-ray tomography of phenotypic switching and the cellular response to antifungal peptoids in Candida albicans

Abstract

The opportunistic pathogen Candida albicans can undergo phenotypic switching between a benign, unicellular phenotype and an invasive, multicellular form that causes candidiasis. Increasingly, strains of Candida are becoming resistant to antifungal drugs, making the treatment of candidiasis difficult, especially in immunocompromised or critically ill patients. Consequently, there is a pressing need to develop new drugs that circumvent fungal drugresistance mechanisms. In this work we used soft X-ray tomography to image the subcellular changes that occur as a consequence of both phenotypic switching and of treating C. albicans with antifungal peptoids, a class of candidate therapeutics unaffected by drug resistance mechanisms. Peptoid treatment suppressed formation of the pathogenic hyphal phenotype and resulted in striking changes in cell and organelle morphology, most dramatically in the nucleus and nucleolus, and in the number, size, and location of lipidic bodies. In particular, peptoid treatment was seen to cause the inclusion of lipidic bodies into the nucleus.

Characterization of transfer function, resolution and depth of field of a soft X-ray microscope applied to tomography enhancement by Wiener deconvolution

“…Most work performed on SXT microscopes addresses samples a few microns thick [4,[12][13][14][15][16][17][18]. Depending on the ratio between the sample thickness and the DOF, standard reconstruction algorithms introduce different artifacts which can be better estimated once the experimental DOF is known [19].…”

Discovery and Characterization of a Peptoid with Antifungal Activity against Cryptococcus neoformans

“…14,15 Although there are significant studies on antibacterial peptoids, 16−21 little research has been performed using peptoids as therapeutic agents against fungi. Nonetheless, studies have successfully demonstrated that peptoids may be used against some fungal pathogens such as Candida albicans, 22 Fusarium virguliforme, and Fusarium lateritium. 23 The need in this field of research is for the rapid identification of antifungal peptoids via high-throughput screening of combinatorial libraries.…”

Optimization of waveguide optics for lensless x-ray imaging

“…Fresnel zone plates replace the condenser and/or objective lenses known from conventional visible light microscopy. This method allows for very high resolution in the soft x-ray spectral range down to 12-15 nm in two-dimensional imaging [1] and of 50 nm in three-dimensional imaging (tomography) [2]. The resolution is not limited by the short x-ray wavelength (nm-to-Å range) but by the focusing properties of the respective optics.…”

“…By application of a support constraint in the exit plane of the two crossed waveguide with a cross section of S = 150 × 150 nm 2 (smoothed by an error function), the near-field intensity in a virtual plane behind the two crossed waveguide can be retrieved iteratively in intensity and phase. Fig.…”

“…15 Regridding is performed using the cubic spline interpolation method (matlab routine interp2.m) [99]. 2) where the error function is given by…”