Acetic acid induces a programmed cell death process in the food spoilage yeast Zygosaccharomyces bailii

Here we show that 320-800 mM acetic acid induces in Zygosaccharomyces bailii a programmed cell death (PCD) process that is inhibited by cycloheximide, is accompanied by structural and biochemical alterations typical of apoptosis, and occurs in cells with preserved mitochondrial and plasma membrane integrity (as revealed by rhodamine 123 (Rh123) and propidium iodide (PI) staining, respectively). Mitochondrial ultrastructural changes, namely decrease of the cristae number, formation of myelinic bodies and swelling were also seen. Exposure to acetic acid above 800 mM resulted in killing by necrosis. The occurrence of an acetic acid-induced active cell death process in Z. bailii reinforces the concept of a physiological role of the PCD in the normal yeast life cycle.Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XX

Rapid detection of efflux pumps and their relation with drug resistance in yeast cells

Cell drug resistance can be due to the presence of active efflux pumps (AEP). Identification of yeast cells with a resistance phenotype is important either from a clinical, agricultural or biotechnological point of view. Rapid and reliable methods to detect AEP can be therefore very useful. Some yeast cells change their staining by cal-cein-AM, BCECF-AM, rhodamine 123 and DiOC5,when pretreated with verapamil, CCCP or ATP depletion, or when pretreated with specific antimicrobial agents. This fact may be interpreted as an indication of the presence/absence of AEP. Six yeast species were tested with a flowcytometric method (FCM) and an epifluorescence micro-scopic method (EFM), and ten other species were evalu-ated only by EFM. The minimum inhibitory concentration(MIC) of penconazol, benomyl and cycloheximide for Saccharomyces cerevisiae and Kluyveromyces marxia-nus, were determined by growth inhibition on solid me-dium and were compared to the staining changes de-tected by FCM. The FCM and the EFM allowed the detection of AEP in all the yeast species tested. High MIC values for adrug were related with the presence of at least one AEP indicated by the cytometric data. The FCM revealed to be a robust assay where as the EFM can be used as a preliminary test. It is possible to identify resistance/sensitivity patterns in yeast cells through cytometric detection methods of different efflux pumping systems.info:eu-repo/semantics/publishedVersio

Fluorometric determination of ethidium bromide efflux kinetics in Escherichia coli

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Contributos da citologia analítica para estudos de biologia de leveduras

Neste artigo começamos por apresentar uma breve introdução à citologia analítica descrevendo alguns conceitos importantes desta disciplina bem como um dos instrumentos que a torna possível - o citómetro de fluxo. Referimos alguns dos aspectos relevantes desta instrumentação, em particular a possibilidade de medir a estrutura e o funcionamento de células vivas e de separar sub-populações celulares para posterior obtenção de culturas puras. Discutimos ainda os fundamentos de algumas aplicações e apresentamos os resultados obtidos nos nossos laboratórios com os seguintes estudos: i) efeitos de fungicidas no ciclo celular de leveduras; ii) relação entre a presença de proteínas de efluxo activas e a menor susceptibilidade de leveduras a antifúngicos; iii) avaliação de alterações estruturais e funcionais induzidas pelo ácido acético e sua relação com perda de viabilidade celular em populações de Saccharomyces cerevisiae e Zygosaccharomyces bailii; iv) determinação do potencial de membrana mitocondrial e avaliação da função mitocondrial de leveduras; v) determinação da ploidia de DNA em leveduras; vi) monitorização in vivo de processos celulares em S. cerevisiae e vii) morte celular programada induzida pelo ácido acético em S. cerevisiae. No decurso destes trabalhos, optimizámos diferentes protocolos de marcação celular recorrendo aos seguintes fl uorocromos: SYBR® Green I para a marcação de DNA; calceína-M, BCECF-AM, Rh123 e DiOC5 para a detecção de proteínas de efl uxo activo; DAF, FUN-1®, IP e Rh123 para a avaliação da integridade estrutural e funcional da célula; Rh123 para a avaliação de potencial de membrana mitocondrial, anexina V-FITC para a detecção de fosfatidilserina no folheto externo da membrana citoplasmática e FITC conjugado com dUTP (reacção de TUNEL) para a detecção de fragmentação internucleosomal de DNA.info:eu-repo/semantics/publishedVersio

Energy conversion coupled to cyanide-resistant respiration in the yeasts Pichia membranifaciens and Debaryomyces hansenii

Cyanide-resistant respiration (CRR) is a widespread metabolic pathway among yeasts, that involves a mitochondrial alternative oxidase sensitive to salicylhydroxamic acid (SHAM). The physiological role of this pathway has been obscure. We used the yeasts Debaryomyces hansenii and Pichia membranifaciens to elucidate the involvement of CRR in energy conversion. In both yeasts the adenosine triphosphate (ATP) content was still high in the presence of antimycin A or SHAM, but decreased to low levels when both inhibitors were present simultaneously, indicating that CRR was involved in ATP formation. Also the mitochondrial membrane potential (v 8 m), monitored by fluorescent dyes, was relatively high in the presence of antimycin A and decreased upon addition of SHAM. In both yeasts the presence of complex I was confirmed by the inhibition of oxygen consumption in isolated mitochondria by rotenone. Comparing in the literature the occurrence of CRR and of complex I among yeasts, we found that CRR and complex I were simultaneously present in 12 out of 13 yeasts, whereas in six out of eight yeasts in which CRR was absent, complex I was also absent. Since three phosphorylating sites are active in the main respiratory chain and only one in CRR, we propose a role for this pathway in the fine adjustment of energy provision to the cell.info:eu-repo/semantics/publishedVersio