Two Novel Aspochalasins from the Gut Fungus Aspergillus sp. Z4

Enhanced production of aspochalasin D through genetic engineering of Aspergillus flavipes

Aspochalasin D (AD) belongs to the polyketide-amino acid hybrid natural products with anti-cancer, anti-bacterial, and anti-fouling bioactivities. However, the low production limits its further application. In this study, AD was separated and identified from Aspergillus flavipes 3.17641. Next, besides the optimization of culture conditions using a single-factor experiment and response surface methodology, metabolic engineering was employed to increase the AD production. It shows that the deletion of the shunt gene aspoA and overexpression of the pathway-specific regulator aspoG significantly improve the AD production. Its production reached to 812.1 mg/L under the optimized conditions, with 18.5-fold increase. Therefore, this study not only provides a general method for improving the production of similar natural products in other fungi, but also enables the further biological function development of AD in agriculture and pharmaceutical. KEY POINTS: • The Aspochalasin D (AD) production was improved by optimizing culture conditions. • The deletion of the shunt gene aspoA increased the AD production. • Overexpression of the pathway regulator aspoG further improved the AD production.

Ultra-high-performance liquid chromatography combined with electrospray ionization quadrupole time-of-flight mass spectrometry and molecular networking analysis to investigate the chemodiversity of bioactive extracts of Annona jahnii Saff. fungi from the Brazilian Amazon

RATIONALE

Annona species are of interest for the isolation of bioactive molecules; however, studies of Annona jahnii Saff. are limited. The exploration of bioactive metabolites of endophytes isolated from this species is unprecedented and allows the preservation of the host plant, in addition to enabling the discovery of compounds with promising biological activities.

METHODS

Ethyl acetate extracts from the cultured media of five fungi were obtained. The antioxidant capacity of the extracts was measured using the 1,1-diphenyl-2-picrylhydrazyl free radical method. Antimicrobial activity was determined using the microdilution method in broth in 96-well plates. The exploration of the metabolic profile of the extracts and dereplication of the compounds were performed using ultra-high-performance liquid chromatography/electrospray ionization/tandem mass spectrometry (UHPLC/ESI-MS/MS) combined with analysis using molecular networking (MN).

RESULTS

A total of 1818 MS features were detected in the five selected extracts, of which 39 compounds were putatively identified. The secondary metabolites with the highest abundance were alkaloids, naphthopyrons, and cytochalasins. Other secondary metabolites include fumonisins, coumarin, and a meroterpenoid. Most of these compounds are related to specific biological properties such as antioxidant, anti-inflammatory, antimicrobial, antiviral, and antitumor activities. Extracts F398 and F403 showed inhibitory activity of the four pathogens tested. Extracts F475 and F506 did not inhibit the growth of Staphylococcus aureus, and F407 did not inhibit the growth of Escherichia coli in addition to having potent antioxidant activity, with IC₅₀ values of 10 μg/mL or less.

CONCLUSIONS

The use of UHPLC/ESI-MS/MS data combined with MN proved useful in the dereplication of bioactive molecules of complex extracts that are still unexplored. These initial investigations should significantly assist in further research and increase the efficiency and speed in the discovery of new sources of secondary metabolites and new natural products.

Ligiamycins A and B, Decalin-Amino-Maleimides from the Co-Culture of Streptomyces sp. and Achromobacter sp. Isolated from the Marine Wharf Roach, Ligia exotica

Streptomyces sp. GET02.ST and Achromobacter sp. GET02.AC were isolated together from the gut of the wharf roach, Ligia exotica, inhabiting the intertidal zone of the west coast of Korea. The co-cultivation of these two strains significantly induced the production of two new metabolites, ligiamycins A (1) and B (2), which were barely detected in the single culture of Streptomyces sp. GET02.ST. The planar structures of ligiamycins A (1) and B (2) were elucidated as new decalins coupled with amino-maleimides by the analysis of various spectroscopic data, including nuclear magnetic resonance (NMR), ultraviolet (UV), and mass (MS) data. The assignment of two nitrogen atoms in amino-maleimide in 1 was accomplished based on 1H-15N heteroatom single quantum coherence spectroscopy (HSQC) NMR experiments. The relative configurations of the ligiamycins were determined using rotating frame Overhauser effect spectroscopy (ROESY) NMR data, and their absolute configurations were deduced by comparing their experimental and calculated optical rotations. Ligiamycin A (1) displayed antibacterial effects against Staphylococcus aureus and Salmonella enterica, while ligiamycin B (2) exhibited mild cell cytotoxicity against human colorectal cancer cells.

Recent updates on the bioactive compounds of the marine-derived genus Aspergillus

The genus Aspergillus is widely distributed in terrestrial and marine environments. In the marine environment, several Aspergillus species have proved their potential to produce a plethora of secondary metabolites including polyketides, sterols, fatty acids, peptides, alkaloids, terpenoids and miscellaneous compounds, displaying a variety of pharmacological activities such as antimicrobial, cytotoxicity, anti-inflammatory and antioxidant activity. From the beginning of 2015 until December 2020, about 361 secondary metabolites were identified from different marine Aspergillus species. In our review, we highlight secondary metabolites from various marine-derived Aspergillus species reported between January 2015 and December 2020 along with their biological potential and structural aspects whenever applicable.

A comprehensive evaluation of the potential of semiterrestrial isopods, Ligia exotica, as a new animal food

The semiterrestrial isopod, Ligia exotica represents one of the oldest documented species introductions of marine organisms and is known as an intermediate form between marine and strictly terrestrial isopods. In order to explore the potential value of Ligia as an animal food source, this study focused on the growth rate under laboratory rearing conditions and conducted a detailed analysis of the overall nutrient content of the species in comparison to two other marine food media (krill and fish meal). Evaluation of the growth rate of juveniles suggests it is a relatively fast-growing species of the Ligiidae family. The essential amino acids content Ligia meal is the lowest amongst the three studied media but the proportion of flavor amino acids, and in particular taurine, was higher. The most restricted amino acids of isopod meal are methionine and cysteine. The significantly unbalanced amino acid composition of Ligia meal may affect the absorption and utilization by consumers. In terms of fatty acids, the total polyunsaturated fatty acids in the isopod is very low. A total of 12 vitamins were examined. The VK_1, VE, VB₂, VB₃, VB₅ content of isopod meal were significantly higher than those of krill meal and fish meal. Similarly, most of the 11 mineral elements are highest in the isopod meal. Ligia therefore offers potential as an alternative natural food source in animal given the growth rate under culture and the overall nutrient content. But Ligia collected in most of the field would be deemed unfit for human consumption because of the relatively low nutritional value and heavy metal content exceeding the provided standard. Further study is warranted to elucidate the biological characteristics of isopods and how its diet is reflected in its nutritional value to consumers.

Marine-derived fungi as a source of bioactive indole alkaloids with diversified structures

Marine-derived fungi are well known as rich sources of bioactive natural products. Growing evidences indicated that indole alkaloids, isolated from a variety of marine-derived fungi, have attracted considerable attention for their diverse, challenging structural complexity and promising bioactivities, and therefore, indole alkaloids have potential to be pharmaceutical lead compounds. Systemic compilation of the relevant literature. In this review, we demonstrated a comprehensive overview of 431 new indole alkaloids from 21 genera of marine-derived fungi with an emphasis on their structures and bioactivities, covering literatures published during 1982-2019.

Natural Products from Marine Fungi

Marine fungi have been studied since the first record of the species Sphaeria posidoniae (Halotthiaposidoniae) on the rhizome of the sea grass Posidonia oceanica by Durieu and Montagne in 1846 [1], butthey have largely been neglected, even though it is estimated that there are greater than 10,000 marinefungal species [...].

Recent Discovery of Heterocyclic Alkaloids from Marine-Derived Aspergillus Species

Nitrogen heterocycles have drawn considerable attention due to of their significant biological activities. The marine fungi residing in extreme environments are among the richest sources of these basic nitrogen-containing secondary metabolites. As one of the most well-known universal groups of filamentous fungi, marine-derived Aspergillus species produce a large number of structurally unique heterocyclic alkaloids. This review attempts to provide a comprehensive summary of the structural diversity and biological activities of heterocyclic alkaloids that are produced by marine-derived Aspergillus species. Herein, a total of 130 such structures that were reported from the beginning of 2014 through the end of 2018 are included, and 75 references are cited in this review, which will benefit future drug development and innovation.