Bioavailability of Nutritional Resources From Cells Killed by Oxidation Supports Expansion of Survivors in Ustilago maydis Populations

Abstract

After heavy exposure of Ustilago maydis cells to clastogens, a great increase in viability was observed if the treated cells were kept under starvation conditions. This restitution of viability is based on cell multiplication at the expense of the intracellular compounds freed from the damaged cells. Analysis of the effect of the leaked material on the growth of undamaged cells revealed opposing biological activity, indicating that U. maydis must possess cellular mechanisms involved not only in reabsorption of the released compounds from external environment but also in contending with their treatment-induced toxicity. From a screen for mutants defective in the restitution of viability, we identified four genes (adr1, did4, kel1, and tbp1) that contribute to the process. The mutants in did4, kel1, and tbp1 exhibited sensitivity to different genotoxic agents implying that the gene products are in some overlapping fashion involved in the protection of genome integrity. The genetic determinants identified by our analysis have already been known to play roles in growth regulation, protein turnover, cytoskeleton structure, and transcription. We discuss ecological and evolutionary implications of these results.

The response of the melanized yeast Exophiala dermatitidis to gamma radiation exposure

“…In aqueous conditions, γ-radiation generally produces DNA DSBs at a similar rate in all organisms [0.005 DSB/Gy/Mbp (Campa et al, 2005;Daly, 2012;Sharma et al, 2017)] so the number of DSB that correspond to this LD 10 dose in E. dermatitidis [with a genome size of 26.5 Mbp (Chen et al, 2014)] is 397.5. This places it among the most resistant fungi known, similar to C. neoformans (332.5 [Jung et al, 2016;Pacelli et al, 2017;Schultzhaus et al, 2019c)] and U. maydis [500 (Lee and Yarranton, 1982;Holloman et al, 2007;Milisavljevic et al, 2018)]. Insights into fungal-specific IR resistance mechanisms, however, have mostly focused on protection by melanin, and the observations presented here and in other recent studies suggest the phenomenon is far more complex.…”

“…neoformans (332.5 [Jung et al ., ; Pacelli et al ., ; Schultzhaus et al ., )] and U . maydis [500 (Lee and Yarranton, ; Holloman et al ., ; Milisavljevic et al ., )]. Insights into fungal‐specific IR resistance mechanisms, however, have mostly focused on protection by melanin, and the observations presented here and in other recent studies suggest the phenomenon is far more complex.…”

“…Slowing the growth rate by limiting nutrients during recovery from IR exposure has been shown to improve survival in Escherichia coli , S . cerevisiae and mammalian cells (Alper and Gillies, ; Reddy et al ., ; Venkateswaran et al ., ; Milisavljevic et al ., ). This did not occur in E .…”

“…Slowing the growth rate by limiting nutrients during recovery from IR exposure has been shown to improve survival in Escherichia coli, S. cerevisiae and mammalian cells (Alper and Gillies, 1960;Reddy et al, 1976;Venkateswaran et al, 2000;Milisavljevic et al, 2018). This did not occur in E. dermatitidis WT cells plated on minimal medium (MM) containing 0.02% glucose when compared with cells recovered on rich (YPD) medium ( Fig.…”

The transcriptomic and phenotypic response of the melanized yeast Exophiala dermatitidis to ionizing particle exposure

“…More recently, the observation that dozens of mold species could be isolated in and around the damaged nuclear reactor at Chernobyl [15] has sparked interest in fungi outside of Saccharomyces cerevisiae for radiobiological studies, a current that has been bolstered by their ease of transformation, their relatively small genome sizes , and the relative simplicity of fungal growth and irradiation methods [16][17][18][19][20]. Signi cant ndings from studies in these organisms include the stimulation of growth of some fungi by low dose IR [20][21][22]; the possibility that melanin in the cell walls of certain fungi can protect against IR through shielding, free-radical scavenging, or a physiological mechanism [21,23]; the high IR resistance of organisms such as Ustilago maydis [24][25][26][27], Cryptococcus neoformans [19,23,28,29], Cryomyces antarcticus [30], and Exophiala dermatitidis [31]; and the discovery of novel IR-resistanceassociated proteins through transcriptomics and targeted mutagenesis [19,28,31]. A portion of the radioresistance of fungi can be explained by their genome size, which is approximately two orders of magnitude smaller than mammals, and therefore sustains less damage per unit dose of IR, but within fungi there is also considerable variation in resistance that is not explained by genome size or composition (for instance, see [12,[31][32][33]).…”