Marine-Derived Cladosporium sp. MBLC9-138 as a Source of Mycophenolic Acid with Preliminary Antibacterial Activity

Abstract

Marine-derived fungi are important reservoirs of bioactive secondary metabolites, yet the diversity of fungal producers of mycophenolic acid (MPA) remains incompletely explored. In this study, 304 fungal strains were isolated from marine sediments collected from three coastal regions of Vietnam and screened for MPA production using thin-layer chromatography, high-performance liquid chromatography, and LC-MS confirmation. Twenty-five isolates (8.22%) were identified as MPA producers and were preliminarily assigned to the fungal genera Penicillium, Aspergillus, and Cladosporium, with two isolates remaining unidentified, based on morphological characteristics. Strain MBLC9-138 was selected for detailed characterization because it represented a non-Penicillium MPA-producing isolate assigned to Cladosporium. Morphological observations and multilocus sequence analyses based on internal transcribed spacer region (ITS), actin gene (ACT), and beta-tubulin gene (TUB/TUB2) supported its identification as Cladosporium sp. MBLC9-138. HPLC analysis showed that this strain produced 463.25 mg/L MPA after 5 days of cultivation in NaCl-supplemented potato dextrose broth, while the maximum yield reached 632.03 ± 2.39 mg/L at 168 ± 12 h during the late exponential to early stationary phase. The purified MPA extract inhibited Bacillus cereus ATCC 11778, Escherichia coli ATCC 25922, and Staphylococcus aureus ATCC 33591, with MIC values of 16, 32, and 64 µg/mL, respectively. These findings identify Cladosporium sp. MBLC9-138 as a previously underreported marine fungal source of MPA, expand the known taxonomic range of MPA-producing fungi, and support further strain optimization, metabolite purification, and antibacterial characterization.