A catechol-reactive Bacillus velezensis cell-free supernatant promotes Lentinula edodes mycelial growth and elicits an iron-homeostasis-related transcriptional response.

Microbial metabolites offer a potential means of improving edible-fungus cultivation, but the response of Lentinula edodes to catechol-reactive bacterial secretions is poorly defined. We quantified species- and concentration-dependent effects of Bacillus velezensis BAC81712 cell-free supernatant, normalized as 2,3-dihydroxybenzoic acid (2,3-DHBA) equivalents, and characterized the L. edodes response using growth, biomass, biochemical, RNA-seq, and qRT-PCR measurements. Among three edible fungi, L. edodes showed the largest response; at 3 µmol/L, its colony-growth AUC was 32.54% above the sterile-KMB control. An exploratory supernatant from dhbB-expressing Escherichia coli produced a comparable growth-associated phenotype, although it was not used for gene-specific inference because a matched vector control was unavailable. RNA sequencing of CK and the native B. velezensis-supernatant condition identified 28 FDR-significant genes. GH64- and GH81-like transcripts decreased significantly, whereas Fet3-, ferric-reductase-, and Ftr1-like candidates increased at the nominal level. qRT-PCR measurements agreed in direction with RNA-seq. Together, the data establish a concentration-dependent whole-supernatant phenotype in L. edodes and associate it with a selective iron-homeostasis- and cell-wall-related transcriptional response. Active-metabolite identity and causal mechanism remain targets for a separate compound-focused study.