Marine-derived fungi Trichoderma genus are serving as a valuable resource for structurally novel natural products encompassing a variety of chemical substances and diverse pharmacological applications. So far, about 78 metabolites have been structurally documented from the species of marine Trichoderma genus and a large proportion of these metabolites exhibited therapeutic properties with potential application in drug discovery. This mini-review focuses on the structures and bioactivities of these secondary metabolites from marine-derived Trichoderma species.
The in situ application of iChip cultivation in mangrove sediment from Hainan province, China, led to the isolation of a novel bacterial species Gallaecimonas mangrovi HK‐28. The extract of G. mangrovi HK‐28 exhibited antibiotic activity against the aquatic pathogen Vibrio harveyi, and its chemical constituents were further investigated by bioactivity‐guided isolation. Three new diketopiperazines, gallaecimonamides A–C, were accordingly isolated from the AcOEt extract of the fermentation broth of G. mangrovi HK‐28. The planar structures of gallaecimonamides A–C were determined using HR‐ESI‐MS together with 1D‐ and 2D‐NMR. The absolute configurations of gallaecimonamides A–C were assigned by optical rotation, NOESY experiment and TDDFT ECD calculations. The in vitro antibacterial and antimalarial activities of gallaecimonamides A–C were assessed. Gallaecimonamide A was found to display antibacterial activity against V. harveyi with a MIC value of 50 μm. However, gallaecimonamides B and C showed no antibacterial activity against V. harveyi (MIC >300 μm). In addition, all the isolates did not exhibit any inhibitory activities against V. parahaemolyticus (MIC>300 μm) and Plasmodium falciparum W2 (EC50>100 μg/mL).
A Gram-stain negative, rod-shaped, non-motile, strictly aerobic bacterium HK-28 was isolated from a mangrove sediment sample in Haikou city, Hainan Province, China. Strain HK-28 was able to grow at 10-45 °C (optimum 25-30 °C), pH 5.0-8.5 (optimum 6.0-7.0) and 0.5-12.0% (w/v) NaCl (optimum 1.0-3.0%, w/v). The major cellular fatty acids were C, Summed Feature 8 (C ω7c and/or C ω6c), Summed Feature 3 (C ω7c and/or C ω6c), C, C 3-OH and Cω8c. Ubiquinone-8 (Q-8) was the predominant respiratory quinone. The polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, two unidentified aminophospholipids, four unidentified phospholipids, two unidentified glycolipid, an unidentified glycophospholipid, an unidentified aminolipid and an unidentified lipid. The DNA G+C content was 50.2 mol%. Accoroding to 16S rRNA gene sequence similarities, strain HK-28 shared 97.1 and 96.7% sequence similarities to the validly named species Gallaecimonas xiamenensis MCCC 1A01354 and Gallaecimonas pentaromativorans MCCC 1A06435, respectively, and shared lower sequence similarities (< 92.0%) to all other genera. Phylogenetic analysis showed strain HK-28 was clustered with G. pentaromativorans MCCC 1A06435 and G. xiamenensis MCCC 1A01354. Strain HK-28 showed low DNA-DNA relatedness with G. xiamenensis MCCC 1A01354 (28.3 ± 1.5%) and G. pentaromativorans MCCC 1A06435 (25.2 ± 2.4%). On the basis of phenotypic, chemotaxonomic and genotypic characteristics, strain HK-28 is considered to represent a novel species in the genus Gallaecimonas, for which the name Gallaecimonas mangrovi sp. nov. is proposed. The type strain is HK-28 (= KCTC 62177 = MCCC 1K03441).
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