Amino Acid Elicitation for Improved Hypocrellin A Biosynthesis in Shiraia bambusicola Under Elevated Fermentation Temperature

Abstract

Hypocrellin A (HA) is a perylenequinone photosensitizer produced by Shiraia bambusicola during submerged fermentation, but its accumulation during submerged fermentation remains limited by low biosynthetic efficiency. Building on our previous finding that 32 °C increased HA accumulation and induced broad transcriptional changes, we reanalyzed that transcriptome to guide amino acid (AA) supplementation. Five AAs (Ala, Lys, Gly, Val, and Ile) were selected from eight residues showing nominal enrichment in proteins encoded by 32 °C upregulated genes because their catabolic routes are among those connected to central carbon metabolism and the generation of acetyl-CoA, the immediate precursor of the HA polyketide backbone. Single AAs and binary combinations were screened for their effects on intracellular HA content in S. bambusicola GDMCC 60438. At 32 °C, single supplementation with Ala (50 mg/L), Lys (200 mg/L), or Gly (100 mg/L) increased intracellular HA content by 71%, 74%, and 36%, respectively. Three binary combinations, Ala + Lys, Ile + Gly, and Val + Gly, further enhanced intracellular HA content by 71%, 75%, and 80%, respectively, with Val + Gly producing the largest increase in intracellular HA content despite Val alone being inactive. The AA response was markedly weaker at 28 °C, with larger response magnitudes observed at 32 °C in separate experiments. Transcriptomic re-analysis of previously published data revealed upregulation of AA transporter genes, including amino acid permeases (AAPs) and major facilitator superfamily (MFS) transporters, at 32 °C. Proteins encoded by highly expressed genes at 32 °C showed enrichment in eight AAs at an unadjusted p < 0.05, seven of which remained significant after Benjamini–Hochberg correction (q < 0.05). Intracellular acetyl-CoA was elevated in AA-supplemented cultures during the early fermentation phase (0–12 h). These findings support a working model in which elevated temperature is associated with a metabolically permissive state under which targeted AA supplementation may enhance HA biosynthesis in independent experiments.