The Biology of Pichia membranifaciens Killer Toxins.
The killer phenomenon is defined as the ability of some yeast to secrete toxins that are lethal to other sensitive yeasts and filamentous fungi. Since the discovery of strains ofSaccharomyces cerevisiaecapable of secreting killer toxins, much information has been gained regarding killer toxins and this fact has substantially contributed knowledge on fundamental aspects of cell biology and yeast genetics. The killer phenomenon has been studied inPichia membranifaciensfor several years, during which two toxins have been described. PMKT and PMKT2 are proteins of low molecular mass that bind to primary receptors located in the cell wall structure of sensitive yeast cells, linear (1→6)-β-d-glucans and mannoproteins for PMKT and PMKT2, respectively. Cwp2p also acts as a secondary receptor for PMKT. Killing of sensitive cells by PMKT is characterized by ionic movements across plasma membrane and an acidification of the intracellular pH triggering an activation of the High Osmolarity Glycerol (HOG) pathway. On the contrary, our investigations showed a mechanism of killing in which cells are arrested at an early S-phase by high concentrations of PMKT2. However, we concluded that induced mortality at low PMKT2 doses and also PMKT is indeed of an apoptotic nature. Killer yeasts and their toxins have found potential applications in several fields: in food and beverage production, as biocontrol agents, in yeast bio-typing, and as novel antimycotic agents. Accordingly, several applications have been found forP. membranifacienskiller toxins, ranging from pre- and post-harvest biocontrol of plant pathogens to applications during wine fermentation and ageing (inhibition ofBotrytis cinerea,Brettanomyces bruxellensis, etc.).
Department of Microbiology, Biology Faculty, Complutense University of Madrid, 28040 Madrid, Spain. ignaciobelda@ucm.es.
Ignacio
I
Belda
Department of Microbiology, Biology Faculty, Complutense University of Madrid, 28040 Madrid, Spain. javiru02@ucm.es.
Javier
J
Ruiz
Department of Microbiology, Biology Faculty, Complutense University of Madrid, 28040 Madrid, Spain. raalonso@ucm.es.
Alejandro
A
Alonso
Department of Microbiology, Biology Faculty, Complutense University of Madrid, 28040 Madrid, Spain. dommarq@ucm.es.
Domingo
D
Marquina
Department of Microbiology, Biology Faculty, Complutense University of Madrid, 28040 Madrid, Spain. ansantos@ucm.es.
Antonio
A
Santos
D006801:Humans; D055646:Killer Factors, Yeast / Q000096:biosynthesis / Q000633:toxicity; D010843:Pichia / Q000302:isolation & purification / Q000378:metabolism
D055646:Killer Factors, Yeast; C087906:killer toxin, Pichia
PMKT; PMKT2; Pichia membranifaciens; applications; biochemical characteristics; biocontrol; killer toxin; mechanism of action