: The biosynthesis of penicillin G (PG) is compartmentalized, which forces penicillin and its intermediates to cross the membrane barriers. Although many aspects around the penicillin intermediates traffic system remain unclosed, the transmembrane transporter protein involvement has been only predicted. In the present work, detection of PG and isopenicillin N (IPN) in Monascus ruber M7 was performed and functions of mfst gene as a transporter were investigated by the combination of gene deletion (Δmfst) complementation (ΔmfsT::mfsT) and overexpression (M7::PtrpC-mfsT). While, the feeding of PG pathway precursor side chain and amino acids, i.e., phenylacetic acid, D-valine, and L-cysteine was performed for the interpretation of mfsT gene role as an intermediate transporter. The results showed that, the feeding of phenylacetic acid, D-valine, and L-cysteine possessed a significant effect on morphologies, secondary metabolites (SMs) production of all above-mentioned strains including M. ruber M7. The results of UPLC-MS/MS revealed that, ΔmfsT interrupt the penicillin G (PG) production in M. ruber M7 by blocking the IPN transportation, while PG and IPN produced by the ΔmfsT::mfsT have been recovered the similar levels to those of M. ruber M7. Conclusively, these findings suggest that the M. ruber M7 is, not only a PG producer, but also, indicate that the mfsT gene is supposed to play a key role in IPN intermediate compound transportation during the PG production in M. ruber M7.

The quality improvement of aquatic raw materials through fermentation assisted by fruit- and vegetable-derived ingredients has attracted increasing attention in aquatic food processing. This study investigated the interactions between spontaneously fermented Chinese cabbage juice (SFCCJ) and tilapia fillets during marination pretreatment and characterized changes in physicochemical properties, flavor compounds, and microbial communities of the fillets during subsequent fermentation. SFCCJ pretreatment enriched fermentable substrates (reducing and total sugars) and functional components (phenolics, flavonoids, and nitrate) in tilapia fillets, reduced inter-sample variability in the initial microbial community, and increased the abundances of Pantoea, Weissella, and Lactobacillus. During subsequent fermentation, L* and a* values increased, while hardness, chewiness, and shear force decreased by up to 19.78%, 73.12%, and 44.02%, respectively, and springiness increased by 25.35%. Meanwhile, FAAs, IMP, AMP, lactic and acetic acids accumulated, accompanied by increases in characteristic volatiles such as linalool, 1-heptanol, benzaldehyde, E-2-hexenal, 3-octanone, and 2-hexanone. In contrast, fishy odor-related compounds, including 2-ethyl-1-hexanol, E-2-octenal, and diallyl disulfide, decreased. LAB, particularly Weissella, Lactobacillus, and Lactococcus, dominated the microbial community from 12 h onward. Microbial metabolic network analysis further showed that these genera were closely associated with physicochemical changes and flavor development, whereas Pantoea, Enterobacter, and Citrobacter were associated with biogenic amine accumulation. These findings provide new insights into the targeted quality improvement of tilapia.