| Summary: | ABSTRACT
The phylum Actinobacteria constitutes one of the largest and anciently divergent phyla
within the Bacteria domain. Actinobacterial diversity has been thoroughly researched
in various environments due to its unique biotechnological potential. Such studies
have focused mostly on soil communities, but more recently marine and extreme
environments have also been explored, finding rare taxa and demonstrating dispersal
limitation and biogeographic patterns for Streptomyces. To test the distribution of
Actinobacteria populations on a small scale, we chose the extremely oligotrophic and
biodiverse Cuatro Cienegas Basin (CCB), an endangered oasis in the Chihuahuan desert
to assess the diversity and uniqueness of Actinobacteria in the Churince System with
a culture-dependent approach over a period of three years, using nine selective media.
The 16S rDNA of putative Actinobacteria were sequenced using both bacteria universal
and phylum-specific primer pairs. Phylogenetic reconstructions were performed to
analyze OTUs clustering and taxonomic identification of the isolates in an evolutionary
context, using validated type species of Streptomyces from previously phylogenies
as a reference. Rarefaction analysis for total Actinobacteria and for Streptomyces
isolates were performed to estimate species’ richness in the intermediate lagoon (IL)
in the oligotrophic Churince system. A total of 350 morphologically and nutritionally
diverse isolates were successfully cultured and characterized as members of the Phylum
Actinobacteria. A total of 105 from the total isolates were successfully subcultured,
processed for DNA extraction and 16S-rDNA sequenced. All strains belong to the order
Actinomycetales, encompassing 11 genera of Actinobacteria; the genus Streptomyces
was found to be the most abundant taxa in all the media tested throughout the 3-
year sampling period. Phylogenetic analysis of our isolates and another 667 reference
strains of the family Streptomycetaceae shows that our isolation effort produced 38
unique OTUs in six new monophyletic clades. This high biodiversity and uniqueness
of Actinobacteria in an extreme oligotrophic environment, which has previously been
reported for its diversity and endemicity, is a suggestive sign of microbial biogeography
of Actinobacteria and it also represents an invaluable source of biological material for
future ecological and bioprospecting studies.
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