Response to vanadate exposure in Ochrobactrum tritici strains.

Vanadium is a transition metal that has been added recently to the EU list of Raw Critical Metals. The growing needs of vanadium primarily in the steel industry justify its increasing economic value. However, because mining of vanadium sources (i. e. ores, concentrates and vanadiferous slags) is expanding, so is vanadium environmental contamination. Bioleaching comes forth as smart strategy to deal with supply demand and environmental contamination. It requires organisms that are able to mobilize the metal and at the same time are resistant to the leachate generated. Here, we investigated the molecular mechanisms underlying vanadium resistance in Ochrobactrum tritici strains. The highly resistant strain 5bvl1 was able to grow at concentrations > 30 mM vanadate, while the O. tritici type strain only tolerated < 3 mM vanadate concentrations. Screening of O. tritici single mutants (chrA, chrC, chrF and recA) growth during vanadate exposure revealed that vanadate resistance was associated with chromate resistance mechanisms (in particular ChrA, an efflux pump and ChrC, a superoxide dismutase). We also showed that sensitivity to vanadate was correlated with increased accumulation of vanadate intracellularly, while in resistant cells this was not found. Other up-regulated proteins found during vanadate exposure were ABC transporters for methionine and iron, suggesting that cellular responses to vanadate toxicity may also induce changes in unspecific transport and chelation of vanadate.

Effect of the Novel Antifungal Drug F901318 (Olorofim) on Growth and Viability of Aspergillus fumigatus.

F901318 (olorofim) is a novel antifungal drug that is highly active against Aspergillus species. Belonging to a new class of antifungals called the orotomides, F901318 targets dihydroorotate dehydrogenase (DHODH) in the de novo pyrimidine biosynthesis pathway. In this study, the antifungal effects of F901318 against Aspergillus fumigatus were investigated. Live cell imaging revealed that, at a concentration of 0.1 µg/ml, F901318 completely inhibited germination, but conidia continued to expand by isotropic growth for >120 h. When this low F901318 concentration was applied to germlings or vegetative hyphae, their elongation was completely inhibited within 10 h. Staining with the fluorescent viability dye bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC) showed that prolonged exposure to F901318 (>24 h) led to vegetative hyphal swelling and a decrease in hyphal viability through cell lysis. The time-dependent killing of F901318 was further confirmed by measuring the fungal biomass and growth rate in liquid culture. The ability of hyphal growth to recover in drug-free medium after 24 h of exposure to F901318 was strongly impaired compared to that of the untreated control. A longer treatment of 48 h further improved the antifungal effect of F901318. Together, the results of this study indicate that F901318 initially has a fungistatic effect on Aspergillus isolates by inhibiting germination and growth, but prolonged exposure is fungicidal through hyphal swelling followed by cell lysis.

Thigmo Responses: The Fungal Sense of Touch.

The growth and development of most fungi take place on a two-dimensional surface or within a three-dimensional matrix. The fungal sense of touch is therefore critical for fungi in the interpretation of their environment and often signals the switch to a new developmental state. Contact sensing, or thigmo-based responses, include thigmo differentiation, such as the induction of invasion structures by plant pathogens in response to topography; thigmonasty, where contact with a motile prey rapidly triggers its capture; and thigmotropism, where the direction of hyphal growth is guided by physical features in the environment. Like plants and some bacteria, fungi grow as walled cells. Despite the well-demonstrated importance of thigmo responses in numerous stages of fungal growth and development, it is not known how fungal cells sense contact through the relatively rigid structure of the cell wall. However, while sensing mechanisms at the molecular level are not entirely understood, the downstream signaling pathways that are activated by contact sensing are being elucidated. In the majority of cases, the response to contact is complemented by chemical cues and both are required, either sequentially or simultaneously, to elicit normal developmental responses. The importance of a sense of touch in the lifestyles and development of diverse fungi is highlighted in this review, and the candidate molecular mechanisms that may be involved in fungal contact sensing are discussed.