Figure 4. Neighbour-joining 16S rRNA gene tree highlighting presumptively novel Modestobacter species isolated from Atacama Desert soils
and species-concepts (Jensen, 2010; Freel et al., 2012). Salinispora arenicola and Salinispora tropica, the founder members of the genus, have a large fraction of their genomes devoted to the biosynthesis of structurally unique secondary metabolites, which are produced in species-specific patterns. Salinispora arenicola synthesizes compounds in the rifampicin and staurosporine classes and S. tropica compounds in the salinosporamide and
sporalide classes, including salinosporamide A which is in clinical trials for the treatment of cancer. The proposed type strain of Salinispora pacifica (Ahmed, pers. com.) produces the secondary metabolite cyanosporoside A which, to date, has not been detected in the other two Salinispora species. Another fascinating, but underexplored, biome that has only recently attracted the attention of
microbe hunters searching for potentially useful Actinobacteria is the temperate Atacama Desert in northern Chile. This is the worldâ&#x20AC;&#x2122;s most continuously arid desert and is also of interest to astrobiologists as the prevailing environmental conditions are considered to provide an accurate analogue of those prevailing in Martian soils. Most Atacama Desert soils are hyper-arid, that is, the ratio of mean annual rainfall to mean annual evaporation is <0.05, the corresponding ratio for the extreme hyper-arid soils of the Yungay region is <0.002. The harshness of these conditions is compounded by high UV radiation, very low concentrations of organic carbon and, in areas such as the Salor de Atacama, by high salinity. The most comprehensive investigation of culturable Actinobacteria from Atacama Desert soils is that of Okoro et al. (2009) who isolated significant numbers of Actinobacteria from arid, hyper-arid and extreme hyper-arid soils using several selective isolation procedures. Genotypic and phenotypic characterization studies showed that most of the isolates were putatively novel Streptomyces species, the remaining isolates formed new centres of taxonomic variation within the rare genera Amycolatopis and Lechevalieria. To date, additional studies have shown that three of the putatively novel streptomycetes do
Table 1. Selected biologically active products of potential value produced by novel actinobacteria isolated from extreme habitats Isolate
Source
Compound
Activity
Dermacoccus abyssi
Sediment, Mariana Trench
Dermacozines
Cytotoxic, radical scavenging
Micromonospora sp.
Marine ascidian
Diazepinomicin
Anticancer
Micromonospora sp.
Sediment (off the Mozambique coast)
Thiocoraline
Anticancer
Nocardiopsis sp.
Fjord sediment, Norway
Thiazolyl peptide
Antibacterial (inhibition of protein synthesis)
Salinispora arenicola
Sediment (off coast of Guam)
Saliniketals
Anticancer
Salinispora arenicola
Sediment (off coast of Palau)
Salinipyrones
Moderate inhibition of interleukin-5 production
Salinispora arenicola
Deep-sea sediment
Salinosporamide A
Anticancer (proteome inhibitor)
Streptomyces sp.
Arid Atacama Desert soil, Chile
Atacamycins
Antitumour
Streptomyces sp.
Hyper-arid Atacama Desert soil, Chile
Chaxamycins
Antibacterial, antitumour
Streptomyces sp.
Sediment, Canary Basin
Carboxamycin
Antibacterial, cytotoxic
Streptomyces sp.
Sediment (off Californian coast)
Marinopyrrols
Antibacterial, antitoxic
Streptomyces sp.
Surface of jellyfish, Florida Keys
Salinamides
Anti-inflammatory
Verrucosispora fiedleri
Sediment, Raune fjord, Norway
Proximicins
Cytotoxic
Verrucosispora maris
Sediment, Sea of Japan
atrop-Abyssomicin C
Antibacterial (inhibition of para-aminobenzoic acid pathway)
Data drawn from Abdel-Mageeb et al., (2010), Goodfellow & Fiedler (2010), Goodfellow et al., (2012b), Santhanam et al., (2012) and Zotchev (2012)
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