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The yeast Pichia fermentans DISAABA 726 strain (P. fermentans) is a dimorphic yeast that under different environmental conditions may switch from a yeast-like to pseudohyphal morphology. We hypothesize that exosomes-like vesicles (EV) could mediate this rapid modification. EV are membrane-derived vesicles carrying lipids, proteins, mRNAs and microRNAs and have been recognized as important mediators of intercellular communication. Although it has been assumed for a long time that fungi release EV, knowledge of their functions is still limited. In this work we analyze P. fermentans EV production during growth in two different media containing urea (YCU) or methionine (YCM) where yeast-like or pseudohyphal morphology are produced. We developed a procedure to extract EV from the neighboring biofilm which is faster and more efficient as compared to the widely used ultracentrifugation method. Differences in morphology and RNA content of EV suggest that they might have an active role during dimorphic transition as response to the growth conditions. Our findings are coherent with a general state of hypoxic stress of the pseudohyphal cells.

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This study focused on crop plant response to a simultaneous exposure to biosolid and TiO at micro-and nano-scale, being biosolid one of the major sink of TiO 2 nanoparticles released into the soil environment. We settled an experimental design as much as possible realistic, at microcosm scale, using the crop Pisum sativum. This experimental design supported the hypotheses that the presence of biosolid in the farming soil might influence plant growth and metabolism and that, after TiO 2 spiking, the different dimension and crystal forms of TiO 2 might be otherwise bioavailable and differently interacting with the plant system. To test these hypotheses, we have considered different aspects of the response elicited by TiO 2 and biosolid at cellular and organism level, focusing on the root system, with an integrative approach. In our experimental conditions, the presence of biosolid disturbed plant growth of P. sativum, causing cellular damages at root level, probably through mechanisms not only oxidative stress-dependent but also involving altered signalling processes. These disturbances could depend on non-humified compounds and/or on the presence of toxic elements and of nanoparticles in the biosolid-amended soil. The addition of TiO 2 particles in the sludgeamended soil, further altered plant growth and induced oxidative and ultrastructural damages. Although non typical dose-effect response was detected, the most responsiveness treatments were found for the anatase crystal form, alone or mixed with rutile. Based on ultrastructural observations, we could hypothesise that the toxicity level of TiO 2 nanoparticles may depend on the cell ability to isolate nanoparticles in subcellular compartments, avoiding their interaction with organelles and/or metabolic processes. The results of the present work suggest reflections on the promising practice of soil amendments and on the use of nanomaterials and their safety for food plants and living organisms.