Fungal Cell Wall Septation and Cytokinesis Are Inhibited by Bleomycins

Abstract

When the essential and distinctive cell walls of either pathogenic or nonpathogenic fungi break, cytoplasmic membranes rupture and fungi die. This fungicidal activity was discovered previously on nonproliferating Saccharomyces cerevisiae cells treated briefly with the oxidative tool and anticancer drug family of bleomycins. The present studies investigated effects of bleomycin on growing fungal organisms. These included the medically important Aspergillus fumigatus and Cryptococcus neoformans, as well as the emerging human pathogen and fungal model, S. cerevisiae. Bleomycin had its highest potency against A. fumigatus. Scanning electron microscopy and thin-section transmission electron microscopy were used to study morphological growth characteristics. Killing and growth inhibition were also measured. Long, thin, and segmented hyphae were observed when A. fumigatus was grown without bleomycin but were never observed when the mold was grown with the drug. Bleomycin arrested conidial germination, hyphal development, and the progression and completion of cell wall septation. Similarly, the drug inhibited the construction of yeast cell wall septa, preventing cytokinesis and progression in the cell division cycle of S. cerevisiae. Even when cytoplasms of mother and daughter cells separated, septation and cell division did not necessarily occur. Bizarre cell configurations, abnormally thickened cell walls at mother-daughter necks, abnormal polarized growth, large undivided cells, fragmented cells, and empty cell ghosts were also produced. This is the first report of a fungicidal agent that arrests fungal growth and development, septum formation, and cytokinesis and that also preferentially localizes to cell walls and alters isolated cell walls as well as intact cell walls on nongrowing cells.The unique cell wall that surrounds fungal cells is absolutely essential for their survival. The cell wall of pathogenic fungi has evolved for survival from environmental factors and host defenses (7,16,18,21,60). The ability of cell walls to evade such factors contributes to the power of pathogenic fungi to cause a wide spectrum of clinical disease (45). Moreover, the unique arrangement of the molecular species forming the structure of the fungal cell wall makes it an excellent target for drug intervention (3,6,24,44,46,54). Thus, the elucidation of the mechanisms of action of agents that interact with the molecules forming the cell walls will yield new insights into fungal cell wall structure, formation of cell walls between dividing cells, and cell division. For fungal pathogens, an understanding of the mechanisms of action of cell wall-specific agents should assist in the design of wall-specific antifungal drugs.Saccharomyces cerevisiae has long been a unicellular fungal model for studies of basic mechanisms. Since this budding yeast is also an emerging opportunistic human pathogen (15,38,42) with properties frequently observed in pathogenic fungi (4,29,30), the yeast is also developing as a model fungal pathogen (12). The dis...

Loss of a 20S Proteasome Activator inSaccharomyces cerevisiaeDownregulates Genes Important for Genomic Integrity, Increases DNA Damage, and Selectively Sensitizes Cells to Agents With Diverse Mechanisms of Action

“…Finally, bleomycin damages fungal cell walls ( Moore et al 1992 ; Beaudouin et al 1993 ; Moore et al 2003 ), as does cell-wall perturbing calcofluor which binds chitin, thereby inhibiting chitin synthase and proper cell wall biosynthesis ( Nitiss and Heitman 2007 ). As Figure 5 shows, cells lacking Blm10 were hypersusceptible to calcofluor.…”

Direct effects of non-antifungal agents used in cancer chemotherapy and organ transplantation on the development and virulence ofCandidaandAspergillusspecies

“…141 Researchers have observed direct activity of bleomycin against A. fumigatus (MIC, 3.2 μg/ml) with arrest of conidial germination, prevention of hyphal development and completion of cell-wall septation. 142 A possible mechanism of cell-wall damage caused by bleomycin is increased cell-wall permeability via disruption of glycosidic cross-linking structures. 142 Other antibiotics.…”

“…142 A possible mechanism of cell-wall damage caused by bleomycin is increased cell-wall permeability via disruption of glycosidic cross-linking structures. 142 Other antibiotics. The sulphonamides, rifampicin and metronidazole have also been studied alone or in combination with polyenes or azoles in vitro and in animal models for their antifungal effects.…”

The regulatory factor X protein MoRfx1 is required for development and pathogenicity in the rice blast fungus Magnaporthe oryzae

“…Interestingly, the FgRFX1 deletion mutant is sensitive to bleomycin in F. graminearum (Min et al ., ). Bleomycin, a DNA‐damaging agent, plays a role not only through the induction of DNA strand breaks (Hecht, ), but also through the blockage of fungal septum formation and cytokinesis by destroying cell wall components via an oxidative mechanism (Beaudouin et al ., ; Lim et al ., ; Moore et al ., ). In F. graminearum , bleomycin inhibits hyphal septum formation and produces micronuclei, and bleomycin‐treated hyphae show many micronuclei and are largely aseptate, as in Δ Fgrfx1 (Min et al ., ).…”