The morphological transformation of yeast cells plays a pivotal role in determining the stability of yeast-based oil-rich wastewater treatment systems. Although metal ions are recognized as important regulators of microbial physiology, their role and underlying mechanisms in controlling yeast morphological transitions in wastewater treatments remain largely unexplored. Here, we investigated the effects of Zn²⁺ on Candida tropicalis O2, using phenylalanine as a filamentation inducer. Zn²⁺ at 5.0 mM completely suppressed phenylalanine-induced filamentation and markedly improved cell flocculation (247.7 %) and settleability (188.7 %). Integrative transcriptomic and metabolomic analyses indicated that Zn²⁺ likely modulates filamentation through multiple mechanisms: (i) perturbation of the cAMP/PKA signaling pathway; (ii) upregulation of morphology-regulatory genes ( MIG1 , ZCF16 , GAT2 , AAF1 , ZCF17 , ARG83 ) and downregulation of RME1 , UME6 , WOR1 , and BCR1 ; (iii) reduced phenylalanine utilization, accompanied by decreased levels of medium- and long-chain fatty acids and phosphatidylglycerols; and (iv) enhanced secretion of quorum-sensing molecules, including phenethyl alcohol (+54.9 %) and the filamentation inhibitor 2,4-ditert-butylphenol (+126.4 %). Together, these findings indicate that Zn²⁺ reprograms signaling, transcriptional regulation, and lipid metabolism in a coordinated manner, thereby suppressing filamentation and promoting stable yeast aggregation. During 30 days of continuous operation of oil-rich wastewater treatment systems, Zn²⁺ supplementation significantly suppressed yeast morphological transformation, improved sludge flocculation and settleability, and postponed the onset of filamentous bulking. This work uncovers a previously uncharacterized inhibitory effect of Zn²⁺ on yeast filamentation and infers the associated molecular and metabolic mechanisms, suggesting controlled Zn²⁺ supplementation as a potential morphology-control strategy for designing robust and efficient yeast-based wastewater treatment processes. • Zn²⁺ supplementation suppresses yeast filamentation and improves settling. • Multi-omics show Zn²⁺ rewires cAMP/PKA signaling and lipid metabolism. • Zn²⁺ enhances secretion of quorum-sensing inhibitors that block filamentation. • SBR trials confirm Zn²⁺ prevents bulking and maintains COD removal efficiency. • Zn²⁺ acts as a morphology-control strategy for stable yeast wastewater treatment.
Tang et al. (Wed,) studied this question.