Four new polyol polyketides containing a decalin ring, nahuoic acids B–E (1–4), together with a known analogue, nahuoic acid A (5), possessing an unprecedented carbon skeleton, were isolated from a culture broth of the marine-derived Streptomyces sp. SCSGAA 0027. Their structures were determined by detailed analysis of spectroscopic data and chemical transformations including acetonide formation and Mosher’s ester method. Compounds 1–5 showed weak antibiofilm activity against Shewanella onedensis MR-1 biofilm. This is the first series of analogues of the novel selective SETD8 inhibitor nahuoic acid A.

A new symmetric 16-membered macrodiolide, trichobotryside A (1), and two new asymmetric 18-membered macrodiolides trichobotrysides B–C (2–3) were obtained from the deep-sea-derived fungus Trichobotrys effuse DFFSCS021. Their structures were elucidated by extensive spectroscopic analysis. The absolute configurations of 1 and 2 were established by the methanolysis and modified Mosher method. And the methanolysis of both 1 and 2 produced the new compound of 4R,7S,9S-trihydroxyl-2-en-1-methyl decanoate (4). It was rare to obtain an 18-membered macrodiolide from nature. Compound 1 showed strong antifouling activity against Bugula neritina and Balanus amphitrite larvae settlement.

Eight new linear peptides, simplicilliumtides A–H (1–8) were isolated from a culture broth of the deep-sea-derived fungal strain Simplicillium obclavatum EIODSF 020. Their structures were elucidated by spectroscopic analysis, and their absolute configurations were determined by Marfey's method. Compounds 1–2 are linear tetrapeptides possessing a 2-aminobenzoic acid residue. Compounds 3–8 are acetylated linear tri- or di-peptides. Their antifouling, antibacterial, cytotoxic, and acetylcholinesterase inhibiting activities were evaluated. Compound 4 showed strong antifouling activity against Bugula neritina larvae settlement. And 1, 5, 7 and 8 showed weak cytotoxicity towards human leukemia HL-60 or K562 cell line.

Trichobotrysins A–F (1–6), a class of new tetramic acid derivatives with a decalin ring, were characterized from the culture of Trichobotrys effuse DFFSCS021 derived from the deep sea sediment collected from the South China Sea. Their structures were elucidated by extensive spectroscopic analysis. Compounds 1, 2, and 4 exhibited significant selective cytotoxicity against human carcinoma KG-1a cell line with IC50 values of 5.44, 8.97, and 6.16 μM, and obvious antiviral activity towards HSV-1 with IC50 values of 3.08, 9.37, and 3.12 μM, respectively. This is the first time to report the anti-HSV-1 activity of this type of compounds.

Cyclopiamides B–J (1–9), nine new oxindole alkaloids were isolated from the deep-sea-derived fungus Penicllium commune DFFSCS026. Their structures were elucidated by extensive spectroscopic data analysis. Compound 4 contains a rare 2H-pyrrole[2,1-b]pyridine unit, and compounds 8 and 9 are complex polycyclic and polyhydroxy alkaloids. The absolute configurations of 6 and 8 were established by molecular mechanics calculation, quantum chemical computations, and single crystal X-ray diffraction analysis, respectively.

A new pyrrolidinone, nigrospine (1), a new indole alkaloid, nigrospin A (2) and two new citrinins, nigrospins B and C (3-4) were isolated from a culture broth of the marine-derived fungal strain Nigrospora oryzae SCSGAF 0111. Their structures were determined by spectroscopic analysis, and the absolute configurations of 1 and 2 were determined by the Mosher ester technique. Compound 1 contains a rare 2,3-dihydro-benzofuran[2,3-c]2-pyrrolidone skeleton.Nigrospolide A (1) possessing a rare 2,3-dihydro-benzofuran[2,3-c]2-pyrrolidone skeleton, and other three new compounds (3-4) were isolated from a marine fungus Nigrospora oryza.

Four dihydrothiophene-condensed chromones including two new compounds oxalicumones D–E (1–2) and known oxalicumones A–B (3–4), along with five other known chromones were isolated from a culture broth of the marine gorgonian-associated fungus Penicillium oxalicum SCSGAF 0023. The structures of 1–2 were elucidated by spectroscopic analysis. Eleven derivatives 3a–3i and 4a–4b were obtained from the acylation of 3 and 4, respectively. Compounds 1–4, 3a–3e, 3g–3h, and 4b showed significant cytotoxicity against several carcinoma cell lines with IC50 ⩽ 10 μM. And their structure–bioactivity relationship was discussed.

Marine-derived microbial secondary metabolites are promising potential sources of nontoxic antifouling agents. The search for environmentally friendly and low-toxic antifouling components guided us to investigate the antifouling potentials of eight novel fungal isolates from deep-sea sediments of the South China Sea. Sixteen crude ethyl acetate extracts of the eight fungal isolates showed distinct antibacterial activity against three marine bacteria (Loktanella hongkongensis UST950701–009, Micrococcus luteus UST950701–006 and Pseudoalteromonas piscida UST010620–005), or significant antilarval activity against larval settlement of bryozoan Bugula neritina. Furthermore, the extract of Aspergillus westerdijkiae DFFSCS013 displayed strong antifouling activity in a field trial lasting 4 months. By further bioassay-guided isolation, five antifouling alkaloids including brevianamide F, circumdatin F and L, notoamide C, and 5-chlorosclerotiamide were isolated from the extract of A. westerdijkiae DFFSCS013. This is the first report about the antifouling potentials of metabolites of the deep-sea-derived fungi from the South China Sea, and the first stage towards the development of non- or low-toxic antifouling agents from deep-sea-derived fungi.

Two new benzodiazepine alkaloids, circumdatins K and L (1, 2), two new prenylated indole alkaloids, 5-chlorosclerotiamide (3) and 10-epi-sclerotiamide (4), and one novel amide, aspergilliamide B (5), together with six known alkaloids were isolated from the deep-sea-derived fungus Aspergillus westerdijkiae DFFSCS013. Their structures were elucidated by extensive spectroscopic analysis. All of the compounds were tested for cytotoxicity toward human carcinoma A549, HL-60, K562, and MCF-7 cell lines.

A new cytotoxic and antiviral cyclic tetrapeptide, asperterrestide A (1), a new alkaloid, terremide C (2), and a new aromatic butenolide, aspernolide E (3), together with 10 known compounds were isolated from the fermentation broth of the marine-derived fungus Aspergillus terreus SCSGAF0162. Their structures were elucidated by spectroscopic analysis, and the absolute configuration of 1 was determined by the Mosher ester technique and analysis of the acid hydrolysates using a chiral-phase HPLC column. Compound 1 contains a rare 3-OH-N-CH3-Phe residue and showed cytotoxicity against U937 and MOLT4 human carcinoma cell lines and inhibitory effects on influenza virus strains H1N1 and H3N2.

Two new polyketides, 6,8,5′6′-tetrahydroxy-3′-methylflavone (1) and paecilin C (2), together with six known analogs secalonic acid D (3), secalonic acid B (4) penicillixanthone A (5), emodin (6), citreorosein (7) and isorhodoptilometrin (8) were obtained from a broth of gorgonian coral-associated fungus Penicillium sp. SCSGAF 0023. Compounds 1 and 6–8 had significant antifouling activity against Balanus amphitrite larvae settlement with EC50 values of 6.7, 6.1, 17.9 and 13.7 μg ml−1, respectively, and 3–5 showed medium antibacterial activity against four tested bacterial strains. This was the first report of antibacterial activity of 3–5 against marine bacteria and antifouling activity of 6–8 against marine biofouling organism’s larvae. The results indicated that gorgonian coral-associated fungus Penicillium sp. SCSGAF 0023 strain could produce antifouling and antibacterial compounds that might aid the host gorgonian coral in protection against marine pathogen bacteria, biofouling organisms and other intruders.

This study describes the diversity and antibacterial activity of culturable actinobacteria isolated from five species of gorgonian corals (Echinogorgia aurantiaca, Melitodes squamata, Muricella flexuosa, Subergorgia suberosa, and Verrucella umbraculum) collected in shallow water of the South China Sea. A total of 123 actinobacterial isolates were recovered using ten different isolation media, and assigned to 11 genera, including Streptomyces and Micromonospora as the dominant genera, followed by Nocardia, Verrucosispora, Nocardiopsis, Rhodococcus, Pseudonocardia, Agrococcus, Saccharomonospora, Saccharopolyspora and Dietzia. Comparable analysis indicated that the numbers of actinobacterial genera and isolates from the five gorgonian coral species varied significantly. It was found that 72 isolates displayed antibacterial activity against at least one indicator bacterium, and the antibacterial strains isolated from different gorgonians had almost the same proportion (~50 %). These results provide direct evidence for the hypotheses that gorgonian coral species contain large and diverse communities of actinobacteria, and suggest that many gorgonian-associated actinobacteria could produce some antibacterial agents to protect their hosts against pathogens. To our knowledge, this is the first report about the diversity of culturable actinobacteria isolated from gorgonian corals.

We investigated the diversity of fungal communities in nine different deep-sea sediment samples of the South China Sea by culture-dependent methods followed by analysis of fungal internal transcribed spacer (ITS) sequences. Although 14 out of 27 identified species were reported in a previous study, 13 species were isolated from sediments of deep-sea environments for the first report. Moreover, these ITS sequences of six isolates shared 84–92 % similarity with their closest matches in GenBank, which suggested that they might be novel phylotypes of genera Ajellomyces, Podosordaria, Torula, and Xylaria. The antimicrobial activities of these fungal isolates were explored using a double-layer technique. A relatively high proportion (56 %) of fungal isolates exhibited antimicrobial activity against at least one pathogenic bacterium or fungus among four marine pathogenic microbes (Micrococcus luteus, Pseudoaltermonas piscida, Aspergerillus versicolor, and A. sydowii). Out of these antimicrobial fungi, the genera Arthrinium, Aspergillus, and Penicillium exhibited antibacterial and antifungal activities, while genus Aureobasidium displayed only antibacterial activity, and genera Acremonium, Cladosporium, Geomyces, and Phaeosphaeriopsis displayed only antifungal activity. To our knowledge, this is the first report to investigate the diversity and antimicrobial activity of culturable deep-sea-derived fungi in the South China Sea. These results suggest that diverse deep-sea fungi from the South China Sea are a potential source for antibiotics’ discovery and further increase the pool of fungi available for natural bioactive product screening.

Many marine natural products hold great potential for the development of new and much needed drugs. However, the production of active metabolites by marine-derived microorganisms is usually very low, and large-scale culture has to be involved to meet the need of chemical structural modification and deep pharmacy study. In order to enhance the production of a novel cytotoxic sulfur-containing chromone oxalicumone A (OA), germinating spores of a marine-derived wild strain Penicillium oxalicum SCSGAF 0023 were mutated by microwave and ultraviolet light irradiation, which led to the obtainment of a mutant P. oxalicum SCSIO 24–2 that could produce fivefold increase in OA production (3.42 ± 0.21 mg/l) as compared to the wild strain. This is the first report that germinating spores are applied in marine-derived Penicillium sp. mutating to enhance the production of OA. Further, Plackett–Burman design and central composite design were adopted to optimize the basic medium components for increasing OA production by the mutant SCSIO 24–2 in shake flasks. The results indicated that three medium components including mannitol, maltose, and l-cysteine had significant effects on OA production, and their concentrations were optimized as 36, 27.9, and 0.99 g/l, respectively. In the optimized medium, the OA production (18.31 ± 0.27 mg/l) by mutant SCSIO 24–2 was 4.4-fold higher than that in the basic medium. These results of this work promise to improve the present production of OA and may be adopted to enhance other objective products' production by marine-derived fungi.

Marine microorganisms have proved to be an important source of pharmacologically active metabolites, and a growing number of marine-derived fungi have been reported to produce metabolites with unique structures and interesting biological activities.1, 2 The genus Aspergillus (Moniliaceae), with over 180 species, has attracted considerable attention as a rich source of alkaloids, terpenoids, xanthones, polyketides and etc, some of which showed antifungal, antibacterial, anti-HIV and cytotoxic activities.3, 4, 5 In order to obtain new bioactive metabolites from marine fungi, we investigated on the marine fungal strain Aspergillus sydowii SCSIO 00305 isolated from a healthy tissue of Verrucella umbraculum. Bioassay-guided fractionation led to the isolation of a new indole diketopiperazine alkaloid, cyclotryprostatin E (1), together with nine known ones, [4-(2-methoxyphenyl)-1-piperazinyl][(1-methyl-1H-indol-3-yl)]-methanone (2), cyclotryprostatin B (3),6 fumiquinazoline D (4),7 fumitremorgin B (5),8 fumiquinazoline C (6),7 fumiquinazoline B (7),7 fumiquinazoline A (8),7 fumiquinazoline F (9),7 fumiquinazoline G (10)7 from a culture broth of the strain. The structures of compounds (1) and (2) were characterized by spectroscopic data interpretation. Compound (2) was a synthetical compound, however, no reference for it. The NMR data and biology source of (2) were reported for the first time. We present herein the fermentation, isolation, structure elucidation and cytotoxicity of compounds (1) and (2).Compound (1) was obtained as pale yellow powder with the molecular formula C23H29N3O6 deduced from NMR spectra and positive HRESIMS (found 466.1953 [M+Na]+, calculated 466.1954). The UV bands (221, 293 nm) and IR absorptions at 3400, 3312, 1664 and 1653 cm−1 indicated the presence of conjugated system, hydroxyl and carbonyl groups. The 1H NMR spectrum of (1) showed two methyl groups (δH 1.34 and 1.47), two methoxyl groups (δH 3.41 and 3.83), and three aromatic protons [δH 7.46 (d, J=9.0 Hz, H-16), 6.75 (dd, J=2.5, 9.0 Hz, H-17), 6.95 (d, J=2.5 Hz, H-19)]. The 13C and DEPT NMR spectra showed signals for 23 carbons, including two methyls (δC 29.1, 31.5), four methylene groups (δC 22.7, 30.9, 46.4 and 50.8), one oxygenated methine carbon (δC 77.6), two oxygenated quaternary carbons (δC 71.2 and 87.3), eight olefinic carbons, and two amide carbonyl groups (δC 167.8 and 169.0). These NMR data of (1) showed similarity to those of (3),3 which suggested that (1) was an indole diketopiperazine alkaloid. A spin coupling system of H2-7/H2-8/H2-9 in the 1H-1H COSY spectrum (Figure 1), combined with HMBC correlations from H-16 to C-14/C-18/C-20, from H-19 to C-15/C-17/C-18/C-20, from H-3/H2-7 to C-5, and from H-6 to C-11 (Figure 1), further confirmed the suggestion. Comparison of 1H- and 13C NMR data of (1) with those of cyclotryprostatin B (3) revealed that a tri-substituted double bond (δC 123.5 and 137.9) in (3) was replaced by an oxygenated quaternary carbon (δC 71.2) and a methylene group (δC 50.8) in (1). In the HMBC spectrum (Figure 1), correlations from H3-23/H3-24/H-3 to C-21/C-22 suggested the assignment of C-21 (δC 50.8) and C-22 (δC 71.2). The relative stereochemistry of (1) was determined by the NOESY spectrum, the magnitude of 1H-1H COSY coupling constants, and comparison of the 13C NMR data of (1) with those of (3). The observed NOE correlations between H-3 and H3-24/H2−21, between H3-24 and H2-21, and between H-6 and H-7α/H-8α, together with nearly identical carbon chemical shift of C-12 (δC 87.3 in (1) and 84.7 in (3)) and C-13 (δC 77.6 in (1) and 76.8 in (3)), indicated that (1) had the same relative configuration as 3.Compound (2) was isolated as pale yellow crystals with the molecular formula C21H23N3O2 deduced from HRESIMS (m/z at 350.1865 [M+H]+, calc. 350.1869). The 1H-, 13C-, and DEPT NMR spectra displayed 18 carbon signals, including one conjugated carbonyl group (δC 168.9), nine methines, one methoxyl (δH 3.84, δC 56.0), one methyl (δH 3.84, δC 33.3), one methylene (δC 52.4), and five quaternary carbons. Three spin coupling systems (H-5/H-6/H-7/H-8, H-20/H-21/H-22/H-23, and H-13(17)/H-14(18)) deduced from 1H-1H COSY spectrum, together with HMBC correlations from H-5 to C-3/C-7/C-9, from H-2 to C-3/C-4/C-9, and from H-8 to C-4/C-6 suggested the existence of one indolyl group, one piperazinyl group, and one 1,2-disubstituted phenyl group. One methyl group and one methoxyl group were deduced to be located at N-1 and C-19, respectively, from the observation of HMBC correlations from δH 3.84 (6H, s) to C-2/C-9/C-19. This information coupled with the key HMBC correlations from H-2, H-13 and H-17 to C-11 and from H-14 and H-16 to C-18 enabled us to establish the structure of (2) as shown in Figure 2. We proposal that chorismate acid may be a biogenetic precursor for (2).Compounds (1) and (2) were screened for their cytotoxicity against A549 (lung cancer cell line), A375 (human melanoma cell line) and Hela (Human cervical carcinoma cell) cell lines, using the MTT method with cis-platin as positive control. Compound (2) showed significant cytotoxicity against A375 cell lines with IC50 (half maximal inhibitory concentration) value of 5.7 μM. Compound (1) had no obvious cytotoxicity towards the above mentioned three cell lines.Cyclotryprostatin E (1): pale yellow powder; [α]D25 +28.35 (c 0.23, CH3OH); UV (CH3OH) λmax (log ε) 209 (2.91), 251 (2.03); 1H and 13C NMR data see Table 1; IR (KBr) νmax 3298, 2980, 2914, 1665, 1450, 1418, 1249, 1158, 1110, 1028 cm−1; ESIMS m/z 466 [M+Na]+; HRESIMS m/z 466.1953 [M+Na]+, calculated for C23H29N3O6Na m/z 466.1954).[4-(2-methoxyphenyl)-1-piperazinyl](1-methyl-1H-indol-3-yl)-methanone (2): pale yellow powder; [α]D25 +33.33 (c 0.06, CH3OH); UV (CH3OH) λmax (log ε) 286 (3.84); 1H and 13C NMR data see Table 1; IR (KBr) νmax 3428, 2932, 2831, 1612, 1534, 1500, 1471, 1434, 1238, 1154, 1139, 747 cm−1; ESIMS m/z 466 [M+Na]+; HRESIMS m/z 350.1871 [M+H]+, calculated for C21H23N3O2 m/z 350.1868).The authors are grateful to the National Basic Research Program of China (grant 2010CB833803), the Knowledge Innovation Program of Chinese Academy of Science (grant KSCX2-EW-G-12B), the National Natural Science Foundation of China and Research Grants Council of Hong Kong (NSFC/RGC) Program (grant 40931160435), National Science Foundation of China (grant 40976090) and the Research Supported by the CAS/SAFEA International Partnership Program for Creative Research Teams (grant KZCX2-YW-T001) for financial support. We thank Chuan-Rong Li of South China Sea Institute of Oceanology for his help in measuring NMR data, and Jun-Jun Huang of Guangzhou Medical College for her help in measuring ESIMS data.

Fungi in gorgonians are now known to cause gorgonian diseases, but little attention has been paid to the nature of fungal communities associated with gorgonians. The diversity of culturable fungi associated with six species of healthy South China Sea gorgonians were investigated using a culture-dependent method followed by analysis of fungal internal transcribed spacer sequences. A total of 121 fungal isolates were recovered and identified using the Basic Local Alignment Search Tool search program. These belonged to 41 fungal species from 20 genera. Of these, 30 species and 12 genera are new reports for gorgonians, and the genera Aspergillus and Penicillium were the most diverse and common in the six gorgonian species. Comparison of the fungal communities in the six gorgonian species, together with results from previous relevant studies, indicated that different gorgonian species and the same gorgonian species living in different geographic locations had different fungal communities. The gorgonian Dichotella gemmacea harbored the most fungal species and isolates, while Echinogorgia aurantiaca had the least fungal diversity. Among the six media used for fungal isolation, potato glucose agar yielded the highest isolates (27 isolates), while glucose peptone starch agar had the best recoverability of fungal species (15 species). The antimicrobial activity of the 121 fungal isolates was tested against three marine bacteria and two marine gorgonian pathogenic fungi. A relatively high proportion (38 %) of fungal isolates displayed distinct antibacterial and antifungal activity, suggesting that the gorgonian-associated fungi may aid their hosts in protection against pathogens. This is the first report comparing the diversity of fungal communities among the South China Sea gorgonians. It contributes to our knowledge of gorgonian-associated fungi and further increases the pool of fungi available for natural bioactive product screening.

•A total of 420 fungal OTUs and 170 fungal taxa were recovered from Okinawa Trough.•Illumina sequencing dramatically accelerated the discovery of fungal community in deep-sea sediments.•More than 31.7% and 21.5% sequences were unassigned fungal genera and new reports for deep-sea environments, respectively.•Sordariomycetes was the most diverse and abundant fungal class in deep-sea sediments from Okinawa Trough.The present study investigated the fungal diversity in four different deep-sea sediments from Okinawa Trough using high-throughput Illumina sequencing of the nuclear ribosomal internal transcribed spacer-1 (ITS1). A total of 40,297 fungal ITS1 sequences clustered into 420 operational taxonomic units (OTUs) with 97% sequence similarity and 170 taxa were recovered from these sediments. Most ITS1 sequences (78%) belonged to the phylum Ascomycota, followed by Basidiomycota (17.3%), Zygomycota (1.5%) and Chytridiomycota (0.8%), and a small proportion (2.4%) belonged to unassigned fungal phyla. Compared with previous studies on fungal diversity of sediments from deep-sea environments by culture-dependent approach and clone library analysis, the present result suggested that Illumina sequencing had been dramatically accelerating the discovery of fungal community of deep-sea sediments. Furthermore, our results revealed that Sordariomycetes was the most diverse and abundant fungal class in this study, challenging the traditional view that the diversity of Sordariomycetes phylotypes was low in the deep-sea environments. In addition, more than 12 taxa accounted for 21.5% sequences were found to be rarely reported as deep-sea fungi, suggesting the deep-sea sediments from Okinawa Trough harbored a plethora of different fungal communities compared with other deep-sea environments. To our knowledge, this study is the first exploration of the fungal diversity in deep-sea sediments from Okinawa Trough using high-throughput Illumina sequencing.

Chemical investigation of the deep-sea-derived fungus Aspergillus versicolor SCSIO 41502 resulted in the isolation of three new anthraquinones, aspergilols G-I (1–3), one new diphenyl ether, 4-carbglyceryl-3,3′-dihydroxy-5,5′-dimethyldiphenyl ether (4), and one new benzaldehyde derivative, 2,4-dihydroxy-6-(4-methoxy-2-oxopentyl)-3-methylbenzaldehyde (5), along with 23 known phenolic compounds (6–28). The structures of new compounds were elucidated by extensive spectroscopic analysis. The absolute configuration of 3 was established by CD spectrum and the modified Mosher method. Compounds 2, 3 and 9 had evident antiviral activity towards HSV-1 with EC50 values of 4.68, 6.25, and 3.12 μM, respectively. Compounds 15, 18, 20 and 22–24 showed more potent antioxidant activity than l-ascorbic acid with IC50 values of 18.92–52.27 μM towards DPPH radicals. Comparison of the structures and antioxidant activities of 1–28 suggests that the number of phenolic hydroxyl group that can freely rotate can significantly affect the antioxidant activity of phenolic compounds. In addition, 4, 22–24 and 27 had significant antifouling activity against Bugula neritina larval settlement with EC50 values of 1.28, 2.61, 5.48, 1.59, and 3.40 μg/ml, respectively.