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Microorganisms are a valuable source of pharmaceutically active chemicals, serving as scaffolds for synthesis as well as lead structures. Investigating novel biomes frequently yields intriguing chemistry; the Atacama Desert in Chile is one such example. This study reports the isolation of a new reduced anthracycline-related compound from the Atacama Desert-derived bacterium Saccharothrix S26. Structural characterisation was achieved by one-dimensional and two-dimensional NMR, HR-LCMS, and X-ray crystallography. The compound was tested against the ESKAPE pathogens, bovine mastitis-related pathogens, and the fungal strain Cryptococcus neoformans, but no antimicrobial activity was observed. [ABSTRACT FROM AUTHOR]

Two novel Micromonospora strains, STR1-7 T and STR1S-6 T , were isolated from the rhizosphere of a Parastrephia quadrangularis plant growing in the Salar de Tara region of the Atacama Desert, Chile. Chemotaxonomic, cultural and phenotypic features confirmed that the isolates belonged to the genus Micromonospora . They grew from 20 to 37 °C, from pH7 to 8 and in the presence of up to 3 %, w/v NaCl. The isolates formed distinct branches in Micromonospora gene trees based on 16S rRNA gene sequences and on a multi-locus sequence analysis of conserved house-keeping genes. A phylogenomic tree generated from the draft genomes of the isolates and their closest phylogenetic neighbours showed that isolate STR1-7 T is most closely related to Micromonospora orduensis S2509 T , and isolate STR1S-6 T forms a distinct branch that is most closely related to 12 validly named Micromonospora species, including Micromonospora saelicesensis the earliest proposed member of the group. The isolates were separated from one another and from their closest phylogenomic neighbours using a combination of chemotaxonomic, genomic and phenotypic features, and by low average nucleotide index and digital DNA-DNA hybridization values. Consequently, it is proposed that isolates STR1-7 T and STR1S-6 T be recognized as representing new species in the genus Micromonospora , namely as Micromonospora parastrephiae sp. nov. and Micromonospora tarensis sp. nov.; the type strains are STR1-7 T (=CECT 9665 T =LMG 30768 T ) and STR1S-6 T (=CECT 9666 T =LMG 30770 T ), respectively. Genome mining showed that the isolates have the capacity to produce novel specialized metabolites, notably antibiotics and compounds that promote plant growth, as well as a broad-range of stress-related genes that provide an insight into how they cope with harsh abiotic conditions that prevail in high-altitude Atacama Desert soils.

The taxonomic status, biotechnological and ecological potential of several Micromonospora strains isolated from an extreme hyper arid Atacama Desert soil were determined. Initially, a polyphasic study was undertaken to clarify the taxonomic status of five micromonosporae, strains LB4, LB19, LB32 T , LB39 T and LB41, isolated from an extreme hyper-arid soil collected from one of the driest regions of the Atacama Desert. All of the isolates were found to have chemotaxonomic, cultural and morphological properties consistent with their classification in the genus Micromonospora. Isolates LB32 T and LB39 T were distinguished from their nearest phylogenetic neighbours and proposed as new species, namely as Micromonospora arida sp. nov. and Micromonospora inaquosa sp. nov., respectively. Eluted methanol extracts of all of the isolates showed activity against a panel of bacterial and fungal indicator strains, notably against multi-drug resistant Klebsiella pneumoniae ATCC 700603 while isolates LB4 and LB41 showed pronounced anti-tumour activity against HepG2 cells. Draft genomes generated for the isolates revealed a rich source of novel biosynthetic gene clusters, some of which were unique to individual strains thereby opening up the prospect of selecting especially gifted micromonosporae for natural product discovery. Key stress-related genes detected in the genomes of all of the isolates provided an insight into how micromonosporae adapt to the harsh environmental conditions that prevail in extreme hyper-arid Atacama Desert soils.

Bio-guided fractionation of the culture broth extract of Streptomyces asenjonii strain KNN 42.f recovered from an extreme hyper-arid Atacama Desert soil in northern Chile led to the isolation of three new bioactive β-diketones; asenjonamides A-C (1-3) in addition to the known N-(2-(1H-indol-3-yl)-2-oxoethyl)acetamide (4), a series of bioactive acylated 4-aminoheptosyl-β-N-glycosides; spicamycins A-E (5-9), and seven known diketopiperazines (10-16). All isolated compounds were characterized by HRESIMS and NMR analyses and tested for their antibacterial effect against a panel of bacteria.

The Atacama Desert is the most extreme non-polar biome on Earth, the core region of which is considered to represent the dry limit for life and to be an analogue for Martian soils. This study focused on actinobacteria because they are keystone species in terrestrial ecosystems and are acknowledged as an unrivalled source of bioactive compounds. Metagenomic analyses of hyper-arid and extreme hyper-arid soils in this desert revealed a remarkable degree of actinobacterial 'dark matter', evidenced by a detected increase of 34% in families against those that are validly published. Rank-abundance analyses indicated that these soils were high-diversity habitats and that the great majority of designated 'rare' genera (up to 60% of all phylotypes) were always rare. These studies have enabled a core actinobacterial microbiome common to both habitats to be defined. The great majority of detected taxa have not been recovered by culture dependent methods, neither, with very few exceptions, has their functional ecology been explored. A microbial seed bank of this magnitude has significance not just for Atacama soil ecosystem resilience but represents an enormous untapped resource for biotechnology discovery programmes in an era where resistance to existing antibiotics is rapidly becoming a major threat to global health.

Interests in the Atacama Desert of northern Chile until very recently were founded on its mineral resources, notably nitrate, copper, lithium and boron. Now this vast desert, the oldest and most arid on Earth, is revealing a microbial diversity that was unimagined even a decade or so ago; indeed the extreme hyper-arid core of the Desert was considered previously to be completely devoid of life. In this Perspective article we highlight pioneering research that, to the contrary, establishes the Atacama as a combination of rich microbial habitats including bacteria that influence biogeochemical transformations in the desert and others that are propitious sources of novel natural products. Many of the Atacama's habitats are especially rich in actinobacteria, not necessarily as dense populations but extensive in taxonomic diversity and capacities to synthesize novel secondary metabolites. Among the latter, compounds have been characterized that express a range of antibiotic, anti-cancer and anti- inflammatory properties to which a variety of bioinformatics and metabolic engineering tools are being applied in order to enhance potencies and productivities. Unquestionably the Atacama Desert is a living desert with regard to which future microbiology and biotechnology research presents exciting opportunities.

The taxonomic position of a Streptomyces strain isolated from an extreme hyper-arid soil sample collected from the Atacama Desert was determined using a polyphasic approach. The strain, isolate C60(T), had chemical and morphological features typical of members of the genus Streptomyces and formed a distinct phyletic line in the Streptomyces 16S rRNA gene tree, together with the type strain of Streptomyces radiopugnans. The two strains were distinguished readily using a combination of phenotypic properties and by a DNA-DNA relatedness value of 23.17 (± 0.95)%. On the basis of these genotypic and phenotypic data, it is proposed that isolate C60(T) (=CGMCC 4.7018(T)=KACC 15492(T)) be classified in the genus Streptomyces as Streptomyces atacamensis sp. nov.

The taxonomic position of a Streptomyces strain isolated from a hyper-arid desert soil was established using a polyphasic approach. The organism had chemical and morphological properties typical of the genus Streptomyces and formed a phyletic line at the periphery of the Streptomyces coeruleorubidus subcluster in the 16S rRNA gene tree. DNA:DNA relatedness values between the isolate and its nearest phylogenetic neighbours, Streptomyces lomondensis NRRL 3252(T) and Streptomyces lusitanus NRRL B-12501(T) were 42.5 (±0.48)% and 25.0 (±1.78)%, respectively. The isolate was readily distinguished from these organisms using a combination of morphological and phenotypic properties. On the basis of these results, it is proposed that isolate C63(T) (CGMCC 4.6997(T), = KACC 15425(T)) be classified as the type strain of Streptomyces deserti sp. nov.

Three new 22-membered macrolactone antibiotics, atacamycins A-C, were produced by Streptomyces sp. C38, a strain isolated from a hyper-arid soil collected from the Atacama Desert in the north of Chile. The metabolites were discovered in our HPLC-diode array screening and isolated from the mycelium by extraction and chromatographic purification steps. The structures were determined by mass spectrometry and NMR experiments. Atacamycins A, B and C exhibited moderate inhibitory activities against the enzyme phosphodiesterase (PDE-4B2), whereas atacamycin A showed a moderate antiproliferative activity against adeno carcinoma and breast carcinoma cells.

The Atacama Desert presents one of the most extreme environments on Earth and we report here the first extensive isolations of actinomycetes from soils at various locations within the Desert. The use of selective isolation procedures enabled actinomycetes to be recovered from arid, hyper-arid and even extreme hyper-arid environments in significant numbers and diversity. In some cases actinomycetes were the only culturable bacteria to be isolated under the conditions of this study. Phylogenetic analysis and some phenotypic characterisation revealed that the majority of isolates belonged to members of the genera Amycolatopsis, Lechevalieria and Streptomyces, a high proportion of which represent novel centres of taxonomic variation. The results of this study support the view that arid desert soils constitute a largely unexplored repository of novel bacteria, while the high incidence of non-ribosomal peptide synthase genes in our isolates recommend them as promising material in screening for new bioactive natural products.