Isolation and properties of a chromosome-dependent KHR killer toxin in Saccharomyces cerevisiae.

Abstract

A strain of the yeast Saccharomyces cerevisiae coding for KHR on the chromosome secreted a toxin that kills sensitive yeasts. The transformants of multicopy vectors carrying the KHR gene could secrete 3-4-fold the killer toxin of the donor strain. This toxic substance was purified 80-fold in specific activity from the culture filtrate by gel filtration and hydrophobic column chromatography. The purified toxin gave a single protein band with molecular mass of 20 kDa on SDS-PAGE and had an isoelectric point of pH 5.3. The toxin had novel killer activity against Candida glabrata and S. cerevisiae, but did not affect bacteria, fungi, or other yeasts.

L-A-lus, a New Variant of the L-A Totivirus Found in Wine Yeasts with Klus Killer Toxin-Encoding Mlus Double-Stranded RNA: Possible Role of Killer Toxin-Encoding Satellite RNAs in the Evolution of Their Helper Viruses

“…In addition to the M dsRNA-encoded killer toxins, there are other killer toxins in S. cerevisiae named KHR and KHS. They show weak killer activity and are encoded on chromosomal DNA (18,19). L-BC is another totivirus (ScV-L-BC), frequently accompanying L-A in S. cerevisiae.…”

A New Wine Saccharomyces cerevisiae Killer Toxin (Klus), Encoded by a Double-Stranded RNA Virus, with Broad Antifungal Activity Is Evolutionarily Related to a Chromosomal Host Gene

“…These viruses, called Saccharomyces cerevisiae viruses (ScVs), belong to the Totiviridae family and are cytoplasmically inherited, spreading horizontally by cell-cell mating or by heterokaryon formation (47). In addition to the M dsRNA-encoded killer toxins, other S. cerevisiae killer toxins, named KHR and KHS, showing weak killer activity, are encoded on chromosomal DNA (13,14).The positive strands of both L-A and M viruses contain cis signals in their 3Ј-terminal regions essential for packaging and replication (46). The signal for transcription initiation has been proposed to be present in the first 25 nucleotides (nt) of L-A, probably in the 5Ј-terminal sequence itself (5Ј-GAAAAA).…”

“…These viruses, called Saccharomyces cerevisiae viruses (ScVs), belong to the Totiviridae family and are cytoplasmically inherited, spreading horizontally by cell-cell mating or by heterokaryon formation (47). In addition to the M dsRNA-encoded killer toxins, other S. cerevisiae killer toxins, named KHR and KHS, showing weak killer activity, are encoded on chromosomal DNA (13,14).…”

Alternative Methods to SO2 for Microbiological Stabilization of Wine

“…In Saccharomyces cerevisiae there are four well characterized killer toxins (K1, K2, K28, and Klus), encoded in cytoplasmatically inherited M doublestranded (ds)-RNAs virus coexisting with the helper virus L-A ds-RNA (Magliani et al, 1997;Rodriguez-Cousino et al, 2011). Additionally, two chromosomally encoded toxins, called killer of heat-resistant (KHR) and killer of heat-sensitive (KHS), were also described in Saccharomyces cerevisiae (Goto et al, 1990). However, some yeast species, as Metschnikowia pulcherrima, may inhibit the growth of both Saccharomyces cerevisiae (Aponte & Blaiotta, 2016b) and spoilage yeasts (Brettanomyces/Dekkera, Hanseniaspora, and Pichia) (Oro, Ciani, & Comitini, 2014) by "iron-adsorbing" pigment formation, which depletes the free iron in the medium, thus generating an environment unsuitable for microorganisms requiring such element for their growth (Sipiczki, 2006).…”