Genetic properties of mercury‑tolerant yeast, Pichia kudriavzevii 1P4.

Mercury contamination in commercial products poses serious risks to human health and the environment. The in vitro detection methods using spectroscopy approaches are expensive and have limited practical use. Yeast-based biosensors provide a more affordable and user-friendly alternative. Therefore, the exploration of mercury tolerance yeast is essential to support the sensor properties. In this study, we investigated the mercury tolerance of 10 yeast isolates. Pichia kudriavzevii 1P4 exhibited tolerance up to 1.5 mM HgCl₂ while showing slow growth phenotype as grown in 2 mM HgCl₂. This is the first report to show the ability of this genus of the yeast Pichia to cope with HgCl₂ stress. X-ray spectra showed Hg accumulation in yeast colonies grown in HgCl2, while none was detected in colonies grown without it. This data indicates the capability of 1P4 in the accumulation of Hg as one of the HgCl₂-stress tolerance mechanisms. Whole-genome sequencing of isolate 1P4, using the MGI DNBSEQ-G400 platform, revealed a genome size of 10.8 Mbp across five chromosomes, with a GC content of 38.97%. The largest portions of the genome are involved in translation, amino acid transport, metabolism, and protein modification, based on COG analysis. Key genes potentially contributing to mercury tolerance involve efflux/inorganic ion transport system (e.g., FieF, Acr3/B, and CzcO/D-clusters) and glutathione-associated oxidative stress response (e.g., BtuE and LysX, which encoded glutathione peroxidase and glutathione synthase). Those genes were predominant in COG category of inorganic ion transport and metabolism (P) and defense mechanisms (V). The genome of 1P4 was assembled into 4753 gene clusters, where 2222 of which were shared with the other species of yeast, including Pichia membranifaciens, P. kluyveri, P. inconspicua, S. cerevisiae, and C. albicans. Meanwhile, 921 gene clusters were shared among genera of Pichia spp., only. These findings highlight the genetic profile and mercury-tolerance mechanisms of isolate 1P4, supporting its potential application as a mercury biosensor or bioremediation agent.