Biology subjects

O Cinneide, E.

Publications and source records attributed to O Cinneide, E..

5 recordsLinked to original sources

bioRxiv2026

The hybrid yeast Saccharomyces pastorianus TUM 34/70 repurposes the pseudohyphal growth signaling network to establish a flocculation phenotype

Lager is the most produced beer style world-wide and makes use of the bottom-fermenting hybrid yeast Saccharomyces pastorianus (S. cerevisiae x S. eubayanus). Previous research showed that flocculation in S. pastorianus, in contrast to the top-fermenting ale yeast S. cerevisiae, is triggered by nitrogen starvation. However, the cellular events leading to flocculation in S. pastorianus are not well characterized. Therefore, we conducted a proteomic screen of S. pastorianus TUM 34/70 and identified the protein kinase Ste20p and protein phosphatase regulatory subunit Ypi1p as higher abundant during flocculation. Overexpression of these genes caused a consistent and strong increase in flocculation rate over the complete duration of beer fermentation. Characterization of Ste20p and Ypi1p via a phospho-proteomics screen showed their targeting of proteins whose S. cerevisiae orthologues are involved in pseudohyphal growth. However, in contrast to this, the overexpression of STE20 and YPI1 led instead to the establishment of a flocculation morphology, giving first-time evidence that S. pastorianus repurposes the pseudohyphal signaling network for this phenotype.

microbiology↗

bioRxiv2024

Ancient origin and high diversity of zymocin-like killer toxins in the budding yeast subphylum

Zymocin is a well-characterized killer toxin secreted by some strains of the yeast Kluyveromyces lactis. It acts by cleaving a specific tRNA in sensitive recipient cells. Zymocin is encoded by a killer plasmid or virus-like element (VLE), which is a linear DNA molecule located in the cytosol. We hypothesized that a tRNA-cleaving toxin similar to zymocin may have caused the three parallel changes to the nuclear genetic code that occurred during yeast evolution, in which the codon CUG became translated as Ser or Ala instead of Leu. However, zymocin-like toxins are rare - both among species, and among strains within a species - and only four toxins of this type have previously been discovered. Here, we identified 45 new zymocin-like toxin genes in Saccharomycotina, the budding yeast subphylum, using a novel bioinformatics strategy, and verified that many of them are toxic to S. cerevisiae when expressed. Some of the new toxin genes are located on cytosolic VLEs, whereas others are on VLE-derived DNA integrated into the nuclear genome. The toxins are extraordinarily diverse in sequence and show evidence of positive selection. Toxin genes were found in five taxonomic orders of budding yeasts, including two of the three orders that reassigned CUG codons, indicating that VLEs have been parasites of yeast species for at least 300 million years and that their existence pre-dates the genetic code changes.

evolutionary biology↗

bioRxiv2023

Cytosolic linear DNA plasmids in Saccharomycopsis species

Some budding yeast species contain cytosolic linear DNA plasmids (also called virus-like elements, VLEs) that code for killer toxins that can kill other yeasts. The toxins are anticodon nucleases that cleave a specific tRNA in the cells being attacked, stopping translation. The best known plasmids of this type are the pGKL1/pGKL2 system of Kluyveromyces lactis. pGKL1 is a killer plasmid encoding the toxin zymocin ({gamma}-toxin) which cleaves tRNA-Glu, and pGKL2 is a helper plasmid required for replication and transcription of pGKL1. Here, we investigated similar plasmids in the genus Saccharomycopsis that were originally described in the 1980s. Saccharomycopsis has undergone an evolutionary change of its genetic code, from CUG-Leu to CUG-Ser translation, which we hypothesized could have been driven by a tRNA-cleaving toxin encoded by a cytosolic plasmid. We sequenced a three-plasmid system in S. crataegensis, consisting of apparent killer, immunity, and helper plasmids. The killer plasmid contains genes coding for putative /{beta} (chitin-binding) and {gamma} (ribonuclease) toxin subunits, but the {gamma}-toxin gene is damaged in all the isolates we examined. We inferred the sequence of the intact S. crataegensis {gamma}-toxin and expressed it in Saccharomyces cerevisiae and Kluyveromyces marxianus, but it did not cause a growth defect. We also identified free plasmids, or plasmids integrated into the nuclear genome, in nine other Saccharomycopsis species, including a case of recent interspecies transfer of a plasmid. Our results show that many yeasts in the CUG-Ser2 clade contain, or have in the past contained, plasmids related to those that carry anticodon nucleases.

evolutionary biology↗

bioRxiv2021

Identification of a novel Candida metapsilosis isolate suggests ongoing hybridization.

Candida metapsilosis is a member of the C. parapsilosis species complex, a group of opportunistic human pathogens. Of all the members of this complex, C. metapsilosis is the least virulent, and accounts for a small proportion of invasive Candida infections. Previous studies established that all C. metapsilosis isolates are hybrids, originating from a single hybridization event between two lineages, parent A and parent B. Here, we use MinION and Illumina sequencing to characterize a C. metapsilosis isolate that originated from a separate hybridization. One of the parents of the new isolate is very closely related to parent A. However, the other parent (parent C) is not the same as parent B. Unlike C. metapsilosis AB isolates, the C. metapsilosis AC isolate has not undergone introgression at the Mating Type-like Locus. In addition, the A and C haplotypes are not fully collinear. The C. metapsilosis AC isolate has undergone Loss of Heterozygosity (LOH) with a preference for haplotype A, indicating that this isolate is in the early stages of genome stabilization.

genomics↗

bioRxiv2020

Population genomics of the pathogenic yeast Candida tropicalis identifies hybrid isolates in environmental samples.

Candida tropicalis is a human pathogen that primarily infects the immunocompromised. Whereas the genome of one isolate, C. tropicalis MYA-3404, was originally sequenced in 2009, there have been no large-scale, multi-isolate studies of the genetic and phenotypic diversity of this species. Here, we used whole genome sequencing and phenotyping to characterize 77 isolates C. tropicalis isolates from clinical and environmental sources from a variety of locations. We show that most C. tropicalis isolates are diploids with approximately 2 - 6 heterozygous variants per kilobase. The genomes are relatively stable, with few aneuploidies. However, we identified one highly homozygous isolate and six isolates of C. tropicalis with much higher heterozygosity levels ranging from 36 - 49 heterozygous variants per kilobase. Our analyses show that the heterozygous isolates represent two different hybrid lineages, where the hybrids share one parent (A) with most other C. tropicalis isolates, but the second parent (B or C) differs by at least 4% at the genome level. Four of the sequenced isolates descend from an AB hybridization, and two from an AC hybridization. The hybrids are MTLa/ heterozygotes. Hybridization, or mating, between different parents is therefore common in the evolutionary history of C. tropicalis. The new hybrids were predominantly found in environmental niches, including from soil. Hybridization is therefore unlikely to be associated with virulence. In addition, we used genotype-phenotype correlation and CRISPR-Cas9 editing to identify a genome variant that results in the inability of one isolate to utilize certain branched-chain amino acids as a sole nitrogen source. Author summaryCandida tropicalis is an important fungal pathogen, which is particularly common in the Asia-Pacific and Latin America. There is currently very little known about the diversity of genotype and phenotype of C. tropicalis isolates. By carrying out a phylogenomic analysis of 77 isolates, we find that C. tropicalis genomes range from very homozygous to highly heterozygous. We show that the heterozygous isolates are hybrids, most likely formed by mating between different parents. Unlike other Candida species, the hybrids are more common in environmental than in clinical niches, suggesting that for this species, hybridization is not associated with virulence. We also explore the range of phenotypes, and we identify a genomic variant that is required for growth on valine and isoleucine as sole nitrogen sources.

genomics↗