Antimicrobial Activity of Metabolites Extracted from Marine Actinomycetes

Actinomycetes are free-living bacteria that are widely distributed and found in several habitats. These bacteria are essential organism in soil system, they contribute to agroindustry as the origin of active compounds. Their economical and biotechnological importance lies in the production of bioactive secondary metabolites including anticancer, insecticides, and antibiotic agents, such Actinomycetes–derived agents have been commonly used in both medical and industrial fields. Mainly, different Actinomycetes species isolated from coastal habitats are found to be novel sources of antibiotics. Thus, further investigating Actinomycetes will provide a better understanding of the physiological features and chemical composition of marine Actinomycetes. It also enables to use of large synthetic libraries of derived molecules (e.g., secondary metabolites) to develop biological drugs to combat advanced bacterial infections. Actinomycetes can produce more powerful biological compounds of medicinal and economic importance; moreover, it can provide insight into new antibiotics against different types of pathogens that cause infection to humans and support human health by overcoming complications caused by pathogenic bacteria and drug resistance. In particular, Actinomycetes of marine origin are a promising source of biomedical microbial products and natural products with an interesting microbial activity against many other pathogenic causing microorganisms. They are diverse in nature and have unique chemical compositions. During the past years, many new anti-microbial agents were discovered and deemed powerful therapeutic agents. The discovery of bioactive compounds continues to increase. However, the underlying potential of Actinomycetes has yet to be found. Therefore, this work conducts a review of the antimicrobial activity of metabolites extracted from marine Actinomycetes.

The Anti-Proliferative Activity of Secondary Metabolite from the Marine Streptomyces sp. against Prostate Cancer Cells

Many active substances from marine organisms are produced by symbiotic microorganisms such as bacteria, fungi, and algae. Secondary metabolites from marine actinomycetes exhibited several biological activities and provided interesting drug leads. This study reported the isolation of Lu01-M, a secondary metabolite from the marine actinomycetes Streptomyces sp., with potent anti-proliferative activity against prostate cancers. Lu01-M blocked cell proliferation with IC50 values of 1.03 ± 0.31, 2.12 ± 0.38, 1.27 ± 0.25 μg/mL in human prostate cancer PC3, DU145, and LNCaP cells, respectively. Lu01-M induced cytotoxic activity through multiple mechanisms including cell apoptosis, necroptosis, autophagy, ER stress, and inhibiting colony formation and cell migration. Lu01-M induced cell cycle arrest at the G2/M phase and DNA damage. However, the activity of autophagy induced survival response in cancer cells. Our findings suggested that Lu01-M holds the potential to be developed as an anti-cancer agent against prostate cancers.

Evaluation of the antifungal activity of marine actinomycetes isolates against the phytopathogenic fungi Colletotrichum siamense KA: A preliminary study for new antifungal compound discovery

Marine actinomycetes are being explored to discover potential actinomycetes that produce antifungal compounds. In a previous study, marine actinomycetes isolates from the mangrove ecosystem were found to inhibit growth of the phytopathogenic fungi Colletotrichum siamense KA. In this study, the three of these isolates with the highest antagonistic activity—SM11, SM14, and SM15—were evaluated for their antifungal activity using antibiosis assay. The fermentation was performed in SCB:PDB medium (1:1) for 6, 9, and 12 days. The results showed that SM14 was the strongest potential isolate; it inhibited the growth of C. siamense KA on average up to 64.90% for 12 days on PDA filtrate medium. Molecular identification showed SM14 was closely related to Streptomyces sanyensis, but had differences in morphological and biochemical characteristics compared to SM11 or SM15. This indicated that the three isolates were different strains and may challenge further research on identifying and analyzing their antifungal compounds.

Zhaoshumycins A and B, Two Unprecedented Antimycin-Type Depsipeptides Produced by the Marine-Derived Streptomyces sp. ITBB-ZKa6

Marine actinomycetes are prolific chemical sources of complex and novel natural products, providing an excellent chance for new drug discovery. The chemical investigation of the marine-derived Streptomyces sp. ITBB-ZKa6, from Zhaoshu island, Hainan, led to the discovery of two unique antimycin-type depsipeptides, zhaoshumycins A (1) and B (2), along with the isolation of the four known neoantimycins A (3), F (4), D (5), and E (6). The structures of the new compounds 1 and 2 were elucidated on the basis of the analysis of diverse spectroscopic data and biogenetic consideration. Zhaoshumycins A (1) and B (2) represent a new class of depsipeptides, featuring two neoantimycin monomers (only neoantimycin D or neoantimycins D and E) linked to a 1,4-disubstituted benzene ring via an imino group. Initial toxicity tests of 1–6 in MCF7 human breast cancer cells revealed that compounds 5 and 6 possess weak cytotoxic activity. Further structure–activity relationship analysis suggested the importance of the NH2 group at C-34 in 5 and 6 for cytotoxicity in MCF7 cells.

Solid State Fermentation of Shrimp Shell Waste Using Pseudonocardia carboxydivorans 18A13O1 to Produce Bioactive Metabolites

Marine actinomycetes are prolific microorganisms; however, knowledge of their diversity, distribution, and secondary metabolites is limited. Marine actinomycetes represent an untapped source of novel bioactive compounds. In this study, we investigated shrimp shell as substrates for model production bioactive metabolites from actinomycetes under solid state fermentation (SSF) conditions. A total of fifteen actinomycetes were isolated from six sponges and one tunicate. The isolated actinomycetes were grown on solid shrimp shells. Cultures of actinomycetes were extracted with ethyl acetate (EtOAc) and extracts were bioassayed for activity against Staphylococcus aureus. One isolate 18A13O1 from the sponge, Rhabdastrella globostellata, exhibited antibacterial activity on primary screening compared to the other samples and was chosen for further study. Visualization using SEM showed aerial and substrate mycelia. Through phylogenetic analysis, it was confirmed that isolate 18A13O1 is a Pseudonocardia carboxydivorans. Purification of an EtOAc extract yielded A13B2, which showed a minimum inhibition concentration against S. aureus at 15.6 μg/mL. It can be concluded that this basic information is very important for further studies related to the development of the production of bioactive secondary metabolites through the solid state fermentation process.

Methanol pigment extracts derived from two marine actinomycetes exhibit antibacterial and antioxidant activities

Mesrian DK, Purwaningtyas WE, Astuti RI, Hasan AEZ, Wahyudi AT. 2021. Methanol pigment extracts derived from two marine actinomycetes exhibit antibacterial and antioxidant activities. Biodiversitas 22: 4440-4447. In recent years, natural pigments produced by marine microorganisms, especially actinomycetes, have become an important source of medically valuable drugs and other active compounds. Based on that crucial fact, this study aimed to determine the toxicity, antimicrobial, and antioxidant activities of methanolic pigment extract derived from marine actinomycetes HV11.P3 and SCA54.P2. Both extracts exhibited high toxicity activity based on Brine Shrimp Lethality Test (BSLT). The results showed the lethal concentration 50% (LC50) values of actinomycetes HV11.P3 and SCA54.P2 pigment crude extracts were 94.60 µg/mL and 131.22 mg/mL, respectively. The antimicrobial activity of those extracts was also tested against several microbes and showed the best results for inhibiting against Bacillus subtilis and Escherichia coli. Furthermore, we assessed the antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and the results showed the inhibitory concentration 50% (IC50) values ??of actinomycetes HV11.P3 and SCA54.P2 pigment crude extracts were 231.08 µg/mL and 369.3 µg/mL, respectively. By using GC-MS analysis, we identified chemical compounds of actinomycete pigment crude extracts, revealing that the most dominant compounds were 1H-Purine-2,6-dione, 3,7-dihydro-1,3,7-trimethyl- (CAS) (44.65%) for HV11.P3 and 5-Methoxypyrrolidin-2-one (30.23%) for SCA54.P2. The 16S rRNA gene sequence analysis showed that actinomycete HV11.P3 and actinomycete SCA54.P2 had the closest similarity to Micromonospora chalcea strain 1464-217L and Micromonospora tulbaghiae strain TVU1, respectively. This study revealed that two pigment crude extracts derived from actinimycetes HV11.P3 and SVA54.P2 had antibacterial, antioxidant, and toxicity activities. The actinomycete SCA54.P2 pigment crude extract had the best activity as an antibacterial against E. coli ATCC 8739, while actnomycete HV11.P3 pigment crude extract had the best activity as an antioxidant.