3-hydroxypropionic acid production from Brewer's spent grain with an engineered Issatchenkia orientalis

3-Hydroxypropionic acid (3-HP) is a versatile platform chemical with wide-ranging industrial applications. This study presents a proof-of-concept approach for producing 3-HP from brewer's spent grain (BSG) using a novel one-pot CaO pretreatment method and an engineered, acid-tolerant Issatchenkia orientalis IoDY01H strain. The effects of acid type for pH adjusting of pretreated slurry, nitrogen supplementation, NaHCO₃ addition, and BSG deproteinization were evaluated. Results showed that using pure glucose and xylose as carbon sources, yeast extract-peptone (YPDX) medium enhanced 3-HP titers by 13.3 % compared to synthetic complete (SCDX) medium. NaHCO₃ supplementation further boosted the 3-HP titer to 7.8 g/L, representing a 7.8 % increase over YPDX alone. In BSG hydrolysates, pH adjustment with H₂SO₄ resulted in higher 3-HP production (7.4 g/L) compared to H₃PO₄ (6.8 g/L). Moreover, supplementation with NaHCO₃ further increased the 3-HP titer to 7.7 g/L, while yeast extract-peptone reduced the 3-HP titer to 6.7 g/L by diverting flux toward strain growth and ethanol formation. Notably, deproteinization of BSG improved xylose recovery and achieved the highest 3-HP titer of 8.7 g/L without nitrogen supplementation. This work provides insights into integrating one-pot pretreatment and hydrolysis and robust fermentation without external nitrogen to produce value-added products from biomass feedstocks.