Abstract
The killer strains of Debaryomyces hansenii and Wickerhamomyces anomalus species secrete antimicrobial proteins called killer toxins which are active against selected fungal phytopathogens. In our research, we attempted to investigate the role of plasma membrane pleiotropic drug resistance (PDR) transporters (Pdr5p and Snq2p) in the mechanism of defense against killer toxins. Saccharomyces cerevisiae mutant strains with strengthened or weakened pleiotropic drug resistance due to increased or reduced number of mentioned PDR efflux pumps were tested for killer toxin susceptibility. The present study demonstrates the influence of the Snq2p efflux pump in immunity to W. anomalus BS91 killer toxin. It was also shown that the activity of killer toxins of D. hansenii AII4b, KI2a, MI1a and CBS767 strains is regulated by other transporters than those influencing W. anomalus killer toxin activity. In turn, this might be related to the functioning of the Pdr5p transporter and a complex cross-talk between several regulatory multidrug resistance networks. To the best of our knowledge, this is the first study that reports the involvement of PDR transporters in the cell membrane of susceptible microorganisms in resistance to killer yeasts’ toxins.
Highlights
Killer strains of the species Debaryomyces hansenii and Wickerhamomyces anomalus exhibit antagonistic activity against several yeast species and fungal phytopathogens
Key Contribution: This study reveals that pleiotropic drug resistance (PDR) transporters in S. cerevisiae play a role in resistance to the activity of D. hansenii and W. anomalus killer toxin, wherein the pdr1-3 S. cerevisiae mutant was resistant to W. anomalus toxin and the ∆pdr1∆pdr3 S. cerevisiae mutant was susceptible to it
The present research, with the use of S. cerevisiae mutants in terms of PDR transporters responsible for the extrusion of substances of low molecular mass from cells, demonstrated that the killer effect may depend on the presence and density of PDR pumps in the plasma membrane of sensitive to killer toxin microorganisms, including Pdr5p and
Summary
Killer strains of the species Debaryomyces hansenii and Wickerhamomyces anomalus exhibit antagonistic activity against several yeast species and fungal phytopathogens. They are considered promising biocontrol agents in plant protection [1–12]. Antagonistic activity of D. hansenii and W. anomalus killer strains can be manifested through various mechanisms, including competition for nutrients and space, mycoparasitism, biofilm formation, induction of plants’ immune response to pathogens, and the secretion of antifungal substances, such as volatile organic compounds (VOCs), β-glucanases, and killer toxins [13–18]. Most killer toxins exhibit a two-step killing mechanism. They bind to their specific receptors in the cell wall of susceptible microorganisms. Toxins may exhibit killer mechanisms such as: blockage of DNA synthesis in the cell nucleus, cleavage of selected tRNAs, inhibition of β-1,3-glucan synthesis, disruption of electrochemical ion gradient across the plasma membrane, or enzymatic activity, leading to increased plasma membrane permeability with an eventual lethal effect [21–24]
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