AUTHOR=Venegas Maximiliano , Barahona Salvador , González Ana María , Sepúlveda Dionisia , Zúñiga Gustavo E. , Baeza Marcelo , Cifuentes Víctor , Alcaíno Jennifer 

TITLE=Phenotypic Analysis of Mutants of Ergosterol Biosynthesis Genes (ERG3 and ERG4) in the Red Yeast Xanthophyllomyces dendrorhous

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.01312

DOI=10.3389/fmicb.2020.01312

ISSN=1664-302X

ABSTRACT=<p><italic>Xanthophyllomyces dendrorhous</italic> synthesizes astaxanthin, a carotenoid used in aquaculture. Astaxanthin is synthesized from metabolites of the mevalonate pathway, which are also precursors for sterols biosynthesis. The interruption of the <italic>CYP61</italic> gene, which is involved in the synthesis of ergosterol (mutant CBS.<italic>cyp61</italic><sup>–</sup>), resulted in a phenotype that overproduces carotenoids due to the activation of the SREBP pathway. In this work, we constructed other mutants of ergosterol biosynthesis in this yeast to evaluate whether they have the same phenotype as mutant CBS.<italic>cyp61</italic><sup>–</sup>. By bioinformatic analysis, the <italic>ERG3</italic> and <italic>ERG4</italic> genes of <italic>X. dendrorhous</italic> were identified, and each gene was deleted in the wild-type strain. Mutants CBS.Δ<italic>erg3</italic> and CBS.Δ<italic>erg4</italic> did not produce ergosterol; CBS.Δ<italic>erg3</italic> primarily accumulated episterol, and CBS.Δ<italic>erg4</italic> primarily accumulated ergosta-5,7,22,24(28)-tetraenol. The transcription levels of the <italic>HMGS</italic> gene of the mevalonate pathway were evaluated by RT-qPCR, which showed a slight increase in CBS.Δ<italic>erg4</italic>, but the transcription levels were still 10-fold lower than in strain CBS.<italic>cyp61</italic><sup>–</sup>. Both CBS.Δ<italic>erg3</italic> and CBS.Δ<italic>erg4</italic> did not overproduce carotenoids, even though they do not produce ergosterol. Thus, the results of this study indicate that the absence of ergosterol does not activate the SREBP pathway in <italic>X. dendrorhous</italic>, but rather it depends on other alterations in sterol composition.</p>