Bioactive Natural Products in Actinobacteria Isolated in Rainwater From Storm Clouds Transported by Western Winds in Spain

Abstract

Actinobacteria are the main producers of bioactive natural products essential for human health. Although their diversity in the atmosphere remains largely unexplored, using a multidisciplinary approach, we studied here 27 antibiotic producing Actinobacteria strains, isolated from 13 different precipitation events at three locations in Northern and Southern Spain. Rain samples were collected throughout 2013–2016, from events with prevailing Western winds. NOAA HYSPLIT meteorological analyses were used to estimate the sources and trajectories of the air-mass that caused the rainfall events. Five-day backward air masses trajectories of the diverse events reveals a main oceanic source from the North Atlantic Ocean, and in some events long range transport from the Pacific and the Arctic Oceans; terrestrial sources from continental North America and Western Europe were also estimated. Different strains were isolated depending on the precipitation event and the latitude of the sampling site. Taxonomic identification by 16S rRNA sequencing and phylogenetic analysis revealed these strains to belong to two Actinobacteria genera. Most of the isolates belong to the genus Streptomyces, thus increasing the number of species of this genus isolated from the atmosphere. Furthermore, five strains belonging to the rare Actinobacterial genus Nocardiopsis were isolated in some events. These results reinforce our previous Streptomyces atmospheric dispersion model, which we extend herein to the genus Nocardiopsis. Production of bioactive secondary metabolites was analyzed by LC-UV-MS. Comparative analyses of Streptomyces and Nocardiopsis metabolites with natural product databases led to the identification of multiple, chemically diverse, compounds. Among bioactive natural products identified 55% are antibiotics, both antibacterial and antifungal, and 23% have antitumor or cytotoxic properties; also compounds with antiparasitic, anti-inflammatory, immunosuppressive, antiviral, insecticidal, neuroprotective, anti-arthritic activities were found. Our findings suggest that over time, through samples collected from different precipitation events, and space, in different sampling places, we can have access to a great diversity of Actinobacteria producing an extraordinary reservoir of bioactive natural products, from remote and very distant origins, thus highlighting the atmosphere as a contrasted source for the discovery of novel compounds of relevance in medicine and biotechnology.

Identification and antibacterial evaluation of endophytic actinobacteria from Luffa cylindrica

“…The present study demonstrated the antibacterial effect and inhibitory potential of endophytic bacteria isolated from L. cylindrica against test bacteria. The results revealed that the crude extracts of the isolates were able to inhibit the growth of at least one of the test bacteria due to the presence of natural bioactive compounds with growth-inhibitory properties 8 , 50 . This finding is consistent with other studies, which reported the endophytic actinobacteria as a potential source of secondary metabolites containing bioactive compounds 50 , 51 .…”

“…The results revealed that the crude extracts of the isolates were able to inhibit the growth of at least one of the test bacteria due to the presence of natural bioactive compounds with growth-inhibitory properties 8 , 50 . This finding is consistent with other studies, which reported the endophytic actinobacteria as a potential source of secondary metabolites containing bioactive compounds 50 , 51 . Some strains such as KUMS-B6 isolate had antagonist activity against both gram-positive and gram-negative bacteria.…”

Overview on Strategies and Assays for Antibiotic Discovery

“…The plug-based diffusion assay has the advantage that the producer can be cultivated independently on different media. Thus, the testing of various antibiotic production conditions is feasible [ 21 , 22 , 23 , 24 , 27 , 44 ]. Recently, a 96-well microplate-based system, suitable for the screening of actinomycete strain collections in agar-plug assays, was established [ 20 ].…”

Natural products, including a new caboxamycin, from Streptomyces and other Actinobacteria isolated in Spain from storm clouds transported by Northern winds of Arctic origin

“…Carlsbergensis. Analyses were performed in TSA1/2 (Merck) against bacteria and in Sabouraud 1/2 (Pronadisa) against yeast, and Frontiers in Chemistry frontiersin.org bioassays were carried out both with agar plugs (7 mm diameter) and also with 6-mm-diameter AA Discs (Whatman), loaded with ethyl acetate extracts of bioactive isolates, as previously reported (Sarmiento-Vizcaíno et al, 2021). Agar plugs assays detect all diffusible compounds produced by actinobacterial strains, both polar and apolar, whereas the AA discs bioassays only detect diffusible apolar molecules extracted with ethyl acetate.…”