Engineering Cell Wall Integrity Enables Enhanced Squalene\nProduction in Yeast

Abstract

Microbial production of many lipophilic\ncompounds is often limited\nby product toxicity to host cells. Engineering cell walls can help\nmitigate the damage caused by lipophilic compounds by increasing tolerance\nto those compounds. To determine if the cell wall engineering would\nbe effective in enhancing lipophilic compound production, we used\na previously constructed squalene-overproducing yeast strain (SQ)\nthat produces over 600 mg/L of squalene, a model membrane-damaging\nlipophilic compound. This SQ strain had significantly decreased membrane\nrigidity, leading to increased cell lysis during fermentation. The\nSQ strain was engineered to restore membrane rigidity by activating\nthe cell wall integrity (CWI) pathway, thereby further enhancing its\nsqualene production efficiency. Maintenance of CWI was associated\nwith improved squalene production, as shown by cell wall remodeling\nthrough regulation of Ecm33, a key regulator of the CWI pathway. Deletion\nof <i>ECM33</i> in the SQ strain helped restore membrane\nrigidity and improve stress tolerance. Moreover, <i>ECM33</i> deletion suppressed cell lysis and increased squalene production\nby approximately 12% compared to that by the parent SQ strain. Thus,\nthis study shows that engineering of the yeast cell wall is a promising\nstrategy for enhancing the physiological functions of industrial strains\nfor production of lipophilic compounds.