A novel Streptomyces zaomyceticus metabolite exhibits antifungal activity against Candida albicans in African catfish

Fungal infection, particularly that caused by Candida albicans, pose emerging challenges in aquaculture, leading to significant economic and health losses in cultured fishes. However, limited research has explored eco-friendly antifungal alternatives for Clarias gariepinus, a species of high commercial value and susceptibility to fungal pathogens. This study aimed to isolate and identify marine-derived Actinobacteria capable of producing potent antifungal compounds effective against C. albicans. An initial screening of 30 Actinobacteria isolates obtained from thirty marine samples collected from Marsa Alam, Egypt was conducted. Among these, Streptomyces zaomyceticus (PQ395286) was identified as a producer of lucidin (1,3-diethoxy-1,1,3,3-tetramethyl lucidin), a novel bioactive metabolite with strong antifungal activity. In vitro assays demonstrated that lucidin inhibited C. albicans (ATCC 10221) with a minimum inhibitory concentration (MIC) of 0.5 μg/mL as confirmed by scanning electron microscopy. To evaluate its in vivo efficacy, C. gariepinus were randomly divided into four groups (three replicates each, 10 fish per replicate). Group 1 served as the negative control (no infection or treatment); Group 2 received lucidin exposure at 100 μg/L through water administration; Group 3 was intraperitoneally infected with C. albicans (3.6 × 104 CFU/fish); and Group 4 was both infected and treated with lucidin. Lucidin treatment markedly alleviated infection-induced alterations in hepatorenal biomarkers, nonspecific immunity, and antioxidant status. It significantly enhanced nitric oxide (NO) production, lysozyme (LYZ) activity, and overall antioxidant capacity. Histological observations confirmed that lucidin effectively restored the normal architecture of the liver, kidney, and spleen. Collectively, these findings highlight lucidin as a promising natural antifungal agent that can effectively mitigate C. albicans infection in C. gariepinus, thereby contributing to the development of sustainable antifungal strategies in aquaculture.