Stress response in medically important Mucorales.

Mucorales are saprobes, ubiquitously distributed and able to infect a heterogeneous population of human hosts. The fungi require robust stress responses to survive in human host. We tested the growth of Mucorales in the presence of different abiotic stress. Eight pathogenic species of Mucorales, including Rhizopus arrhizus, Rhizopus microsporus, Rhizomucor pusillus, Apophysomyces elegans, Licthemia corymbifera, Cunninghamella bertholletiae, Syncephalastrum racemosum and Mucor racemosus, were exposed to different stress inducers: osmotic (sodium chloride and d-sorbitol), oxidative (hydrogen peroxide and menadione), pH, cell wall and metal ions (Cu, Zn, Fe and Mg). Wide variation in stress responses was noted: R. arrhizus showed maximum resistance to both osmotic and oxidative stresses, whereas R. pusillus and M. indicus were relatively sensitive. Rhizopus arrhizus and R. microsporus showed maximum resistance to alkaline pH, whereas C. bertholletiae, L. corymbifera, M. racemosus and A. elegans were resistant to acidic pH. Maximum tolerance was noted in R. microsporus to Cu, R. microsporus and R. arrhizus to Fe and C. bertholletiae to Zn. In contrast, L. corymbifera, A. elegans and M. indicus were sensitive to Cu, Zn and Fe respectively. In conclusion, R. arrhizus showed high stress tolerance in comparison to other species of Mucorales, and this could be the possible reason for high pathogenic potential of this fungi.

Heat shock response of thermophilic fungi: membrane lipids and soluble carbohydrates under elevated temperatures.

The heat shock (HS) response is an adaptation of organisms to elevated temperature. It includes substantial changes in the composition of cellular membranes, proteins and soluble carbohydrates. To protect the cellular macromolecules, thermophilic organisms have evolved mechanisms of persistent thermotolerance. Many of those mechanisms are common for thermotolerance and the HS response. However, it remains unknown whether thermophilic species respond to HS by further elevating concentrations of protective components. We investigated the composition of the soluble cytosol carbohydrates and membrane lipids of the thermophilic fungi Rhizomucor tauricus and Myceliophthora thermophilaat optimum temperature conditions (41-43 °Ð¡), and under HS (51-53 °Ð¡). At optimum temperatures, the membrane lipid composition was characterized by a high proportion of phosphatidic acids (PA) (20-35 % of the total), which were the main components of the membrane lipids, together with phosphatidylcholines (PC), phosphatidylethanolamines (PE) and sterols (St). In response to HS, the proportion of PA and St increased, and the amount of PC and PE decreased. No decrease in the degree of fatty acid desaturation in the major phospholipids under HS was detected. The mycelium of all fungi at optimum temperatures contained high levels of trehalose (8-10 %, w/w; 60-95 % of the total carbohydrates), which is a hallmark of thermophilia. In contrast to mesophilic fungi, heat exposure decreased the trehalose level and the fungi did not acquire thermotolerance to lethal HS, indicating that trehalose plays a key role in this process. This pattern of changes appears to be conserved in the studied filamentous thermophilic fungi.

Serial monitoring of Mucorales DNA load in serum samples of a patient with disseminated mucormycosis after allogeneic bone marrow transplantation.

Mucormycosis is a fatal complication in immunocompromised patients, and is additionally difficult to diagnose due to the lack of useful serum biomarkers. Using a quantitative PCR approach, we retrospectively analyzed Mucorales DNA load in sera collected serially from a 3-year-old patient with chronic granulomatous disease, who died of multi-organ failure probably due to dissemination of Rhizomucor pusillus, which was detected from necropsy specimens. Mucorales DNA load was below the detection limit on days 9, 2, and 4 after unrelated bone marrow transplantation. Rhizomucor DNA was first detected on day 14 (1.6 × 10(3) copies/mL), and subsequently fluctuated between 1.3 × 10(3) and 37.2 × 10(3) copies/mL until day 43. Rhizomucor achieved a peak value of 940.0 × 10(3) copies/mL on day 48 the day before death. The detection or fluctuation of Rhizomucor DNA appeared to be associated with corticosteroid dosages or C-reactive protein levels. This specific, noninvasive, and highly quantitative assay may be useful for the early diagnosis of mucormycosis and prediction of disease progression.

Heterothallic mating in Mucor irregularis and first isolate of the species outside of Asia.

This study reports on the discovery of heterothallic mating in Mucor irregularis (formerly Rhizomucor variabilis var. variabilis) and it extends the range of this species from Asia to the United States. We report on a case of primary cutaneous mucormycosis, involving the forearms of a cotton farmer from North Carolina, in which the infection was cured using amphotericin B therapy. Intraspecific crosses between the North Carolina strain DUMC 150.04 and M. irregularis CBS 103.93, the ex-type strain of R. variabilis var. variabilis from China, resulted in the formation of abundant fertile zygospores. By way of contrast, interspecific crosses between the North Carolina isolate and the ex-neotype strain of M. hiemalis NRRL 3624 resulted in the formation of putative azygospores by M. irregularis DUMC 150.04.

Primary cutaneous mucormycosis caused by Rhizomucor variabilis in an immunocompetent patient.

Primary cutaneous mucormycosis is an uncommon disease and occurs mainly in patients with immunocompromised disorders. We report a case of cutaneous mucormycosis in an immunocompetent man in whom no definite precipitating factors were noted. The isolate was identified as Rhizomucor variabilis according to the fungus morphology and DNA sequencing results. The lesion was successfully treated with oral Itraconazole, although the in vitro drug-susceptibility test showed resistance.