Draft Genome Sequence of the Yeast Starmerella bacillaris (syn., Candidazemplinina) FRI751 Isolated from Fermenting Must of Dried Raboso Grapes.

Starmerella bacillaris is an ascomycetous yeast commonly present in enological environments. Here, we report the first draft genome sequence of S. bacillaris FRI751, which will facilitate the study of the characteristics of this interesting enological yeast.

GENOME ANNOUNCEMENT

The ascomycetous yeast Starmerella bacillaris (syn., Candida zemplinina) is frequently found in spontaneous must fermentation, usually at a relatively high population level of 104 to 106 cells/ml (1), in grape marcs (2), and it is also normally present on botrytized grapes.

This species was isolated for the first time in Napa Valley (CA) in 2002 (3), and 1 year later, Sipiczki (4) assigned this Candida sp. to a novel species under the name Candida zemplinina, due to the significant differences observed in the rRNA sequence from that of the related species Candida stellata (5). For a long time, C. zemplinina has been confounded with its close species C. stellata, which shares similar ecological niches, particularly in grape and wine environments. Finally, it was established as Starmerella bacillaris (6).

S. bacillaris is able to ferment glucose, sucrose, and raffinose but not galactose, maltose, or lactose (6). Unable to grow in vitamin-free medium, it develops well in the presence of high glucose concentration, up to 50% (wt/vol) (6). It is highly fructophilic and a high-glycerol producer (7).

S. bacillaris is a psichrotolerant and osmotolerant species (4), and among the non-Saccharomyces yeasts of enological interest, S. bacillaris is considered one of the most promising species to satisfy modern market and consumer preferences. In particular, it produces less ethanol from must fermentation than Saccharomyces cerevisiae, low levels of biogenic amines, and average volatile acidity (8). It is also being tested in association with Saccharomyces cerevisiae in mixed or sequential fermentations to reduce alcohol content and to increase the organoleptic properties of wines (7), and its possible use in the vineyard as an antifungal agent against Botrytis is under study (8).

In this work, the first genome sequence for an S. bacillaris strain is released. Strain FRI751 was isolated from fermentation of dried grapes of Raboso wine, a vine variety cultivated mainly in the Northeast of Italy for the production of passito wines.

S. bacillaris FRI751 genomic DNA was prepared by zymolyase digestion, followed by standard phenol-chloroform extraction, as described by Vaughan-Martini and Martini (9). The genome sequence was generated using an Illumina NextSeq 500 platform (1-kb mate-pair libraries) at the Ramaciotti Centre, Sydney, Australia. The sequencing generated 45-fold coverage with 1,435,554 paired-end (2 × 150 bp) and 102,368 unpaired reads (after quality filtering) that were used for the de novo assembly by SPAdes 3.10 software (10) (with option -k 21,33,55,77,99,127). The genome size of S. bacillaris FRI751 was 9.3 Mbp, divided into 106 contigs longer than 100 bp (N50 length, 208,744 bp), and the G+C content was 39.4%. Protein-coding gene (CDS) prediction was performed using GeneMark-ES (11) and resulted in 4,028 CDSs and a total of 4,315 exons. Gene annotation was obtained combining two strategies: (i) BlastKOALA (12) was used to search against a nonredundant set of KEGG genes, selecting Saccharomycetaceae as the taxonomy group; and (ii) RPS BLAST was used to compare protein sequences with Eukaryotic Orthologous Groups of proteins (KOG) (13).

The data reported here represent a useful resource to increase the knowledge of S. bacillaris metabolism and of its potential technological characteristics as applied to enology.

Accession number(s).

The whole-genome shotgun project of S. bacillaris FRI751 has been deposited in DDBJ/ENA/GenBank under the accession no. MWSF00000000. The version described in this paper is the first version, MWSF01000000.