5-Hydroxymethyl-2-furancarboxylic acid: An effective antibacterial metabolite derived from Aspergillus niger

The exploration of effective biocontrol agents and the characterization of their functional components are crucial for precisely preventing and managing carrot postharvest disease. Herein, Aspergillus niger xj was shown to effectively inhibit the bacterial soft-rot pathogen named Pectobacterium aroidearum , with the functional compounds primarily localized in the extracellular fermentation broth. Correlation analysis between the inhibitory activity and content of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) across 224 atmospheric and room-temperature plasma mutant strains and original strain xj indicated that HMFCA was an important inhibitory agent. The bioactivity of the bio-derived HMFCA isolated from the positive mutant strain 350–28 was validated through assays. In vitro inhibitory assays revealed that the half-maximal effective concentration (EC 50 ) of HMFCA against P. aroidearum was 1121 ± 8 μg mL −1 , with a minimum inhibitory concentration of 1.25 mg mL −1 and a minimum bactericidal concentration of 2.5 mg mL −1 . Moreover, HMFCA exhibited considerable potential to impede the growth of P. aroidearum . Furthermore, in vivo inhibitory assays indicated that HMFCA could assist carrot in resisting the infection caused by P. aroidearum within 24 h at three concentrations: EC 20 , EC 50 , and EC 80. However, the required effective concentration markedly increased at 48 h. These findings indicated that A. niger exhibited biocontrol activity through the extracellular secretion of active secondary metabolites, which directly suppressed the growth and reproduction of P. aroidearum . In particular, HMFCA was a functional compound, which offered a promising approach for the targeted postharvest management of carrot.