Abstract
Some edible oils are produced by heterotrophic fermentation of Prototheca, a genus of non-photosynthetic green algae. Two accessions from the University of Texas Culture Collection of Algae (UTEX) have been used for oil production: UTEX 1435 historically and UTEX 1533 more recently. Because Prototheca classification methods have been revised and collection labels may now be unreliable, linking UTEX 1533 to the production and regulatory history of UTEX 1435 requires establishing whether they are the same species. We compared UTEX 1533 with archival UTEX 1435 sequences, related deposits, and six disease-associated (“clinical”) isolates using organellar markers, nuclear phylogeny, whole-genome identity, and mitochondrial intron structure. UTEX 1533 matched historical UTEX 1435 at plastid 16S and 23S rRNA, the only available archival loci. UTEX 1533, ATCC 16525 (linked to historical UTEX 1435), and the P. wickerhamii-type strain ATCC 16529 shared identical plastid 16S and 23S and mitochondrial cytb sequences. These accessions formed a fully supported nuclear group, with 95.82–98.04% whole-genome identity, versus 88.72–89.83% to the clinical isolates. Two mitochondrial introns shared by this group were absent from all six clinical isolates. Cultures supplied as UTEX 1435 in 2017 and 2026 instead matched P. xanthoriae. These findings identify UTEX 1533 as P. wickerhamii, conspecific with historical UTEX 1435, and suggest a change in material currently distributed under the UTEX 1435 designation.