# Construction of a reference genome for Starmerella batistae and annotation of Starmerella species reveal an unexpected evolutionary relationship with Schizosaccharomyces pombe and suggest an alternative enzymatic route for sophorolipid production

## TL;DR

Researchers sequenced the genome of an acid-loving yeast, Starmerella batistae, and found it shares genes with another yeast species and has unique ways to produce useful compounds.

## Contribution

The study provides a new reference genome for S. batistae and reveals novel evolutionary connections and alternative sophorolipid production pathways in Starmerella species.

## Key findings

- S. batistae shares 15 unique genes with Schizosaccharomyces pombe, including those related to cell morphology.
- Starmerella species have evolved alternative pathways for sophorolipid production.
- A close evolutionary relationship was found between Starmerella and Schizosaccharomyces yeasts.

## Abstract

The Starmerella clade is known for displaying osmotolerant and acidophilic traits from their association with bees. Several species in this genus can produce sophorolipids, which are commercially produced as biosurfactants. Here, we isolated a yeast contaminant from the laboratory environment, identified as Starmerella batistae, able to thrive at low pH and relative high temperatures. We sequenced and conducted a de novo genome assembly in three chromosomes and a mitochondrial genome for S. batistae (ca. 9.3 Mb). Based on this reference genome we functionally annotated 29 Starmerella species, using the publicly available sequences. Phylogenetic analysis across different yeast clades revealed a close relationship between Starmerella and Schizosaccharomyces yeasts. Fifteen genes were uniquely shared between Schizosaccharomyces pombe and S. batistae, of which twelve were involved in cell morphology, reflecting the fact that S. batistae cells are elongated rather than round. We found that all the Starmerella sophorolipid-producing strains shared a close common ancestor. One-to-one orthologs of Starmerella bombicola sophorolipid pathway were only found in S. kuoi (full pathway, but inverted), and in S. powellii and S. floricola (partial pathway). These findings support the notion that alternative pathways for the production of sophorolipids have evolved in different Starmerella lineages.

The genome of Starmerella batistae, an acidophilic yeast, was sequenced, assembled, annotated, and compared across 29 species, revealing unique genes, evolutionary links to Schizosaccharomycespombe, and diverse sophorolipid biosynthesis pathways.