Viriditins from Byssochlamys spectabilis, their stereochemistry and biosynthesis

Multiplexed mobilization and expression of biosynthetic gene clusters

Bacterial genomes contain large reservoirs of biosynthetic gene clusters (BGCs) that are predicted to encode unexplored natural products. Heterologous expression of previously unstudied BGCs should facilitate the discovery of additional therapeutically relevant bioactive molecules from bacterial culture collections, but the large-scale manipulation of BGCs remains cumbersome. Here, we describe a method to parallelize the identification, mobilization and heterologous expression of BGCs. Our solution simultaneously captures large numbers of BGCs by cloning the genomes of a strain collection in a large-insert library and uses the CONKAT-seq (co-occurrence network analysis of targeted sequences) sequencing pipeline to efficiently localize clones carrying intact BGCs which represent candidates for heterologous expression. Our discovery of several natural products, including an antibiotic that is active against multi-drug resistant Staphylococcus aureus, demonstrates the potential of leveraging economies of scale with this approach to systematically interrogate cryptic BGCs contained in strain collections.

Efficient mobilization and expression of biosynthetic gene clusters (BGCs) into heterologous hosts is needed for microbial natural products discovery. Here, the authors improve the CONKAT-seq strategy by simultaneously capturing the BCGs into a single large insert library and demonstrate its ability to discover natural products with new structures and potent antibacterial activity.

Antimicrobial Terpenoids and Polyketides from the Algicolous Fungus Byssochlamys spectabilis RR-dl-2-13

Four new carotane sesquiterpenoids, byssocarotins A-D (1-4), two new nor-sesquiterpenoids, byssofarnesin (5) and byssosesquicarin (6), and three new polyketides, byssoketides A and B (7 and 8) and (8R)-paecilocin A (9a), were obtained from a macroalga-associated strain (RR-dl-2-13) of the fungus Byssochlamys spectabilis. These isolates were identified by a combination of spectroscopic methods, including mass spectroscopy, nuclear magnetic resonance, electronic circular dichroism, and X-ray diffraction. Compounds 1-4 greatly contribute to the diversity of rarely occurring 2,15-epoxycarotane sesquiterpenoids, while 5 and 6 are degradation products of farnesane and sesquicarane precursors, respectively. Compound 7 is a structurally unique furan fatty acid derivative that possesses an aldehyde group and a large conjugated unit, and 8 features a hemiketal group. During antimicrobial assays, 8 showed antagonism against the phytopathogenic fungi Glomerella cingulata, Fusarium oxysporum f. sp. cucumerium, and F. oxysporum f. sp. cubense and the marine-derived bacteria Vibrio parahaemolyticus and V. harveyi with MIC values of 13 to 50 μg/mL.

Biocontrol Effects of Paecilomyces variotii against Fungal Plant Diseases

The genus Paecilomyces is known for its potential application in the control of pests and diseases; however, its use in agriculture is limited to few species. Research interest in new formulations based on microorganisms for the control of pathogens is growing exponentially; therefore, it is necessary to study new isolates, which may help control diseases effectively, and to examine their compatibility with established agricultural control methods. We analysed in vitro and in vivo the antagonistic capacity of Paecilomyces variotii against seven phytopathogens with a high incidence in different crops, and we examined its compatibility with 24 commercial fungicides. P. variotii was applied in the following pathosystems: B. cinereal—melon, Sclerotinia sclerotiorum—pepper, R. solani—tomato, F. solani—zucchini, P. aphanidermatum—melon, M. melonis—melon, and P. xanthii—zucchini. The results showed strong control effects on M. melonis and P. xanthii, reducing the disease severity index by 78% and 76%, respectively. The reduction in disease severity in the other pathosystems ranged from 29% to 44%. However, application of metabolites alone did not cause any significant effect on mycelial growth of phytopathogens, apart from F. solani, in which up to 12% inhibition was observed in vitro when the extract was applied at a concentration of 15% in the medium. P. variotii was compatible with most of the tested fungicides, and of the 24 fungicides tested at the maximum authorised dose, 6 acted as fungicides, 4 as fungistatics, and the remaining showed inhibition rates ranging from 18.2% to 95.8%. These results indicate that P. variotii is a potential biological control agent to be used against several aerial and soil diseases, thus it should be integrated into modern pest management strategies.

Simplicilones A and B Isolated from the Endophytic Fungus Simplicillium subtropicum SPC3

Two new tetracyclic polyketides with a spirocenter, simplicilones A (1) and B (2) were isolated from the broth-culture of the endophytic fungus Simplicilliumsubtropicum (SPC3) in the course of our screening for new bioactive secondary metabolites. This endophytoic fungus is naturally harboured in the fresh bark of the Cameroonian medicinal plant Duguetia staudtii (Engl. and Diels) Chatrou. The planar structures of the simplicilones were elucidated by MS and 1D as well as 2D NMR spectroscopic techniques. The relative configuration was assigned by NOESY experiments in conjunction with coupling constants; subsequently, the absolute configurations were assigned by the modified Mosher’s method. The compounds showed weak cytotoxic effects against the cell line KB3.1 (in vitro cytotoxicity (IC₅₀) = 25 µg/mL for 1, 29 µg/mL for 2), but were inactive against the tested Gram-positive and Gram-negative bacteria as well as fungi.