The Madeira Archipelago As a Significant Source of Marine-Derived Actinomycete Diversity with Anticancer and Antimicrobial Potential

Abstract

Marine-derived actinomycetes have demonstrated an ability to produce novel compounds with medically relevant biological activity. Studying the diversity and biogeographical patterns of marine actinomycetes offers an opportunity to identify genera that are under environmental pressures, which may drive adaptations that yield specific biosynthetic capabilities. The present study describes research efforts to explore regions of the Atlantic Ocean, specifically around the Madeira Archipelago, where knowledge of the indigenous actinomycete diversity is scarce. A total of 400 actinomycetes were isolated, sequenced, and screened for antimicrobial and anticancer activities. The three most abundant genera identified were Streptomyces, Actinomadura, and Micromonospora. Phylogenetic analyses of the marine OTUs isolated indicated that the Madeira Archipelago is a new source of actinomycetes adapted to life in the ocean. Phylogenetic differences between offshore (>100 m from shore) and nearshore (< 100 m from shore) populations illustrates the importance of sampling offshore in order to isolate new and diverse bacterial strains. Novel phylotypes from chemically rich marine actinomycete groups like MAR4 and the genus Salinispora were isolated. Anticancer and antimicrobial assays identified Streptomyces, Micromonospora, and Salinispora as the most biologically active genera. This study illustrates the importance of bioprospecting efforts at unexplored regions of the ocean to recover bacterial strains with the potential to produce novel and interesting chemistry.

Keywords: Madeira Archipelago; anticancer activity; antimicrobial activity; cultivable bacterial diversity; marine actinomycete phylogeny; marine actinomycetes; marine sediments; natural product discovery.

Figure 1

Rarefaction curves of isolated marine derived actinomycetes from the Madeira Archipelago. Both observed (sobs) and estimated (chao) diversity curves show that saturation has not been reached within the diversity of cultivated marine-derived actinomycetes.

Figure 2

Maximum Likelihood phylogenetic tree of the 16s rRNA gene from 71 representative actinomycete OTUs from the Madeira Archipelago and their GenBank nearest neighbor. The tree was created using 1279 bp and 1000 bootstraps. Numbers in parenthesis are GenBank accession numbers and PTM number refers to internal reference collection number. Stars show those OTUs where strains with a requirement of seawater for growth were observed. Bacillus methanolicus was used as an outgroup.

Figure 3

UniFrac dissimilarity dendograms per habitat (top) and as a group of inshore and offshore samples (bottom).

Figure 4

Maximum Likelihood phylogenetic tree using 16s rRNA (1279 bp and 1000 bootstraps) from Madeira actinomycete strains belonging to the previously described MAR4 group. Reference MAR4 strains were used to create the tree. PTM numbers of the Madeira strains are shown followed by a dark filled circle. Streptomyces rubreogriseus was used as an outgroup.

Figure 5

Maximum Likelihood phylogenetic tree using 16s rRNA (1279 bp and 1000 bootstraps) from Madeira actinomycete strains belonging to the previously described Salinispora genus. Reference Salinispora strains were used to create the tree. Salinispora species are named and followed by their GenBank accession number in parenthesis. PTM numbers of the Madeira strains are shown. Verrucosispora maris was used as an outgroup.