New cyclic tetrapeptide from the coral-derived endophytic bacteria Brevibacterium sp. L-4 collected from the South China Sea

Biofilm-forming bacteria associated with corals secrete melanin with UV-absorption properties

Corals are colonized by a plethora of microorganisms, and their diversity plays a significant role in the health and resilience of corals when they face oxidative stress leading to bleaching. In the current study, we examined 238 bacteria isolated from five different coral species (Acropora hyacinthus, Pocillopora damicornis, Podabacea crustacea, Porites lobata, and Pavona venosa) collected from the coral reef ecosystems of Kavaratti, Lakshadweep Islands, India. We found that bacteria such as Psychrobacter sp., Halomonas sp., Kushneria sp., Staphylococcus sp., Bacillus sp., Brachybacterium sp., Citrobacter sp., and Salinicola sp. were commonly present in the corals. On the other hand, Qipengyuania sp., Faucicola sp., Marihabitans sp., Azomonas sp., Atlantibacter sp., Cedecea sp., Krasalinikoviella sp., and Aidingimonas sp. were not previously reported from the corals. Among the bacterial isolates, a significant number showed high levels of biofilm formation (118), UV absorption (119), and melanin production (127). Considering these properties, we have identified a combination of seven bacteria from the genera Halomonas sp., Psychrobacter sp., Krasalinikoviella sp., and Micrococcus sp. as a potential probiotic consortium for protecting corals from oxidative stress. Overall, this study provides valuable insights into the coral microbiome and opens up possibilities for microbiome-based interventions to protect these crucial ecosystems in the face of global environmental challenges.

Streptomyces Endophytes in Edible Plants: New Insights into their Chemistry and Health Benefits

Streptomyces is the largest source of microbial antibiotics with about 50 % of marketed antimicrobial drugs originating from this genus. Endophytic streptomyces are the link between medicinal plants and the microbial world. Endophytic Streptomyces in edible plants were not targeted before despite their uniqueness and importance. In this review, we analyzed the chemical diversity of more than 150 compounds belonging to endophytic Streptomyces chemical classes such as alkaloids, polyketides, peptides, macrolides and terpenes and their biological activities. This analysis showed a dominant antimicrobial effect for most of the isolated compounds and highlighted an underestimated diversity to be studied or repurposed for other biological activities. Return to edible plants use and conducting toxicity studies to rationalize their nutraceutical potential based on their beneficial endophytes is urged. Although there are many studies for non-vertebrates, the nutraceutical potential of these plants is expected to improve the gut microbiota since they are enriched with bioactive compounds from streptomyces species. This is the first review to discuss edible plants associated streptomyces, and we prospect that many studies will follow to unravel the mysterious health benefits of streptomyces in the human microbiome and encourage the revival of a correct lifestyle for the sake of a healthier microbiome.

The potential of marine-derived piperazine alkaloids: Sources, structures and bioactivities

Marine-derived piperazine alkaloids (MDPAs) constitute a significant group of natural compounds known for their diverse structures and biological activities. Over the past five decades, substantial efforts have been devoted to isolating these alkaloids from marine sources and characterizing their chemical and bioactive profiles. To date, a total of 922 marine-derived piperazine alkaloids have been reported from various marine organisms. These compounds demonstrate a wide range of pharmacological properties, including cytotoxicity, antibacterial, antifungal, antiviral, and various other activities. Notably, among these activities, cytotoxicity emerges as the most prominent characteristic of marine-derived piperazine alkaloids. This review also summarizes the structure-activity relationship (SAR) studies associated with the cytotoxicity of these compounds. In summary, our objective is to provide an overview of the research progress concerning marine-derived piperazine alkaloids, with the aim of fostering their continued development and utilization.

Genome sequence analysis and bioactivity profiling of marine-derived actinobacteria, Brevibacterium luteolum, and Cellulosimicrobium funkei

Genome analysis gives important insights into the biosynthetic potential of marine actinobacteria. The genomes of two marine actinomycetes Brevibacterium luteolum MOSEL-ME10a and Cellulosimicrobium funkei MOSEL-ME6 were sequenced to identify the biosynthetic gene clusters (BGCs). Additionally, anti-proliferative, antioxidant, and enzyme inhibitory activities were studied in vitro. We report a total genome size of 2.77 Mb with GC content of 67.8% and 6.81 Mb with GC content of 69% for Brevibacterium sp. MOSEL-ME10a and Cellulosimicrobium sp. MOSEL-ME6, respectively. Biosynthetic gene clusters (BGCs) encoding different classes of natural products were predicted including terpenes, peptides, siderophores, ectoines, and bacteriocins. The bioactivity potential of crude extracts derived from these strains was evaluated. Notable anti-proliferative activity was observed against HepG2 cell line (hepatocellular carcinoma) with an IC₅₀ value of 182 µg/mL for Brevibacterium sp. MOSEL-ME10a. Furthermore, antioxidant activity was assessed with IC₅₀ values of 48.91 µg/mL and 102.5 µg/mL for Brevibacterium sp. MOSEL-ME10a and Cellulosimicrobium sp. MOSEL-ME6, respectively. Protein kinase inhibition potential was observed only for Brevibacterium sp. MOSEL-ME10a. Our study also reports lower amylase enzyme inhibition potential for both strains. Moreover, both crude extracts showed only slight-to-no toxic effect on erythrocytes at 400 µg/mL and below, indicating erythrocyte membrane stability. Our data present the genomic features revealing biosynthetic potential of marine actinobacteria as well as biological activities found in vitro.

Ecological and biotechnological importance of secondary metabolites produced by coral-associated bacteria

Symbiotic relationships between corals and their associated micro-organisms are essential to maintain host homeostasis. Coral-associated bacteria (CAB) can have different beneficial roles in the coral metaorganism, such as metabolizing essential nutrients for the coral host and protecting the coral from pathogens. Many CAB exert these functions via secondary metabolites, which include antibacterial, antifouling, antitumour, antiparasitic and antiviral compounds. This review describes how analysis of CAB has led to the discovery of secondary metabolites with potential biotechnological applications. The most commonly found types of secondary metabolites, antimicrobial and antibiofilm compounds, are emphasized and described. Recently developed methods that can be applied to enhance the culturing of CAB from shallow-water reefs and the less-studied deep-sea coral reefs are also discussed. Last, we suggest how the combined use of meta-omics and innovative growth-diffusion techniques can vastly improve the discovery of novel compounds in coral environments.

Chemical and Bioactive Marine Natural Products of Coral-Derived Microorganisms (2015-2017)

Coral-derived microorganisms are known for their inherent ability to produce novel products of pharmaceutical importance. Nearly 260 marine natural products (MNPs) have been isolated from coral-derived microorganisms till 2014. In the last three years, 118 MNPs have been isolated from coral-associated microorganisms including 46 new compounds, two with a novel skeleton, and four new natural products. Most of them exhibited in vitro or in vivo activities against tumor cell lines, parasites, pathogenic bacteria, fungi and virus. We reviewed the natural products reported from 2015 to 2017 that have a wide range of bioactivities against different biological targets.

A new uridine derivative and a new indole derivative from the coral-associated actinomycete Pseudonocardia sp. SCSIO 11457

A new uridine derivative 11457 A (1), and a new indole derivative 11457B (2), together with a known compound 1H-indole-2-carbaldehyde (3), were characterized from the fermentation broth of the actinomycete Pseudonocardia sp. SCSIO 11457, an isolate associated with the scleractinian coral Galaxea fascicularis. Upon detailed spectroscopic analysis, 11457 A (1) was identified as a uridine analog, and 11457B (2) was elucidated as an indole derivative 2-hydroxy-1-(1H-indol-2-yl)pentane-1,4-dione. Biological evaluation indicated that none of compounds 1-3 showed antibacterial activities against pathogenic bacteria and cytotoxic activities against human cancer cell lines.

Anti-proliferative potential of cyclotetrapeptides from Bacillus velezensis RA5401 and their molecular docking on G-Protein-Coupled Receptors

Elucidation of bioactive chemical compounds from rhizobacteria is highly utilized in pharmaceuticals and naturopathy, due to their health benefits to human and plants. In current study, four cyclopeptides along with one phenyl amide were isolated from the ethyl acetate extract of Bacillus velezensis sp. RA5401. Their structures were determined and characterized as cycle (L-prolyl-L-leucyl)₂ (1), cyclo (L-prolyl-l-valine)₂ (2), cycle (L-phenylanalyl-L-propyl)₂ (3), cyclo (D-pro-L-tyr-L-pro-L-tyr)₂ (4) and N-(2-phenylethyl)acetamide (5) on the basis of electron spray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR) techniques and comparison with the literature data. The five compounds have been isolated for the first time from this species. The effect of various concentrations of these compounds on the proliferation of MDA-MB-231 breast cancer cells was examined. It was found that 1 and 2 induced concentration-independent anti-proliferative effects, while 3, 4 and 5 inhibited cancer cell proliferation in a concentration-dependent manner. Furthermore, to determine the suitable binding targets of these compounds within cancer cell line, detailed target prediction and comparative molecular-docking studies were performed. The compounds 1 and 2 hit intracellular anti-cancer targets of proteases family, while compounds 3, 4 and 5 interacted with different membrane receptors of G-Protein-Coupled Receptors (GPCRs). In conclusion, the Bacillus velezensis RA5401 can be an ideal strain to produce anti-proliferative constituents at industrial scale.

Heterologous Expression of a VioA Variant Activates Cryptic Compounds in a Marine-Derived Brevibacterium Strain

A new 14-membered homodimeric macrodiolide, brevidiolide (3), along with four known aromatic compounds (1, 2, 4 and 5) were obtained by heterologous expression of the recombinant plasmid pWLI823 expressing the G231L variant of VioA in the marine-derived Brevibacterium sp. 7002-073. The structures of 1–5 were elucidated on the basis of LC-MS and 2D NMR spectroscopic analyses. In the evaluation for the antibacterial activities of the compounds against multi-drug resistant (MDR) strains, 5 showed notable growth inhibition against Staphylococcus aureus CCARM 3090 and Klebsiella pneumoniae ATCC 13883, with a minimum inhibitory concentration (MIC) value of 3.12 µg/mL.

Marine natural products

Covering: 2016. Previous review: Nat. Prod. Rep., 2017, 34, 235-294This review covers the literature published in 2016 for marine natural products (MNPs), with 757 citations (643 for the period January to December 2016) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1277 in 432 papers for 2016), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included.