Publications

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2019
Tuttle, RN, Demko AM, Patin NV, Kapono CA, Donia MS, Dorrestein P, Jensen PR.  2019.  Detection of natural products and their producers in ocean sediments. Applied and Environmental Microbiology. 85   10.1128/aem.02830-18   AbstractWebsite

Thousands of natural products have been identified from cultured microorganisms, yet evidence of their production in the environment has proven elusive. Technological advances in mass spectrometry, combined with public data-bases, now make it possible to address this disparity by detecting compounds directly from environmental samples. Here, we used adsorbent resins, tandem mass spectrometry, and next-generation sequencing to assess the metabolome of marine sediments and its relationship to bacterial community structure. We identified natural products previously reported from cultured bacteria, providing evidence they are produced in situ, and compounds of anthropogenic origin, suggesting this approach can be used as an indicator of environmental impact. The bacterial metabolite staurosporine was quantified and shown to reach physiologically relevant concentrations, indicating that it may influence sediment community structure. Staurosporine concentrations were correlated with the relative abundance of the staurosporine-producing bacterial genus Salinispora and production confirmed in strains cultured from the same location, providing a link between compound and candidate producer. Metagenomic analyses revealed numerous biosynthetic gene clusters related to indolocarbazole biosynthesis, providing evidence for noncanonical sources of staurosporine and a path forward to assess the relationships between natural products and the organisms that produce them. Untargeted environmental metabolomics circumvents the need for laboratory cultivation and represents a promising approach to understanding the functional roles of natural products in shaping microbial community structure in marine sediments. IMPORTANCE Natural products are readily isolated from cultured bacteria and exploited for useful purposes, including drug discovery. However, these compounds are rarely detected in the environments from which the bacteria are obtained, thus limiting our understanding of their ecological significance. Here, we used environmental metabolomics to directly assess chemical diversity in marine sediments. We identified numerous metabolites and, in one case, isolated strains of bacteria capable of producing one of the compounds detected. Coupling environmental metabolomics with community and metagenomic analyses provides opportunities to link compounds and producers and begin to assess the complex interactions mediated by specialized metabolites in marine sediments.

2017
Letzel, AC, Li J, Amos GCA, Millan-Aguinaga N, Ginigini J, Abdelmohsen UR, Gaudencio SP, Ziemert N, Moore BS, Jensen PR.  2017.  Genomic insights into specialized metabolism in the marine actinomycete Salinispora. Environmental Microbiology. 19:3660-3673.   10.1111/1462-2920.13867   AbstractWebsite

Comparative genomics is providing new opportunities to address the diversity and distributions of genes encoding the biosynthesis of specialized metabolites. An analysis of 119 genome sequences representing three closely related species of the marine actinomycete genus Salinispora reveals extraordinary biosynthetic diversity in the form of 176 distinct biosynthetic gene clusters (BGCs) of which only 24 have been linked to their products. Remarkably, more than half of the BGCs were observed in only one or two strains, suggesting they were acquired relatively recently in the evolutionary history of the genus. These acquired gene clusters are concentrated in specific genomic islands, which represent hot spots for BGC acquisition. While most BGCs are stable in terms of their chromosomal position, others migrated to different locations or were exchanged with unrelated gene clusters suggesting a plug and play type model of evolution that provides a mechanism to test the relative fitness effects of specialized metabolites. Transcriptome analyses were used to address the relationships between BGC abundance, chromosomal position and product discovery. The results indicate that recently acquired BGCs can be functional and that complex evolutionary processes shape the micro-diversity of specialized metabolism observed in closely related environmental bacteria.

2016
Schorn, MA, Alanjary MM, Aguinaldo K, Korobeynikov A, Podell S, Patin N, Lincecum T, Jensen PR, Ziemert N, Moore BS.  2016.  Sequencing rare marine actinomycete genomes reveals high density of unique natural product biosynthetic gene clusters. Microbiology-Sgm. 162:2075-2086.   10.1099/mic.0.000386   AbstractWebsite

Traditional natural product discovery methods have nearly exhausted the accessible diversity of microbial chemicals, making new sources and techniques paramount in the search for new molecules. Marine actinomycete bacteria have recently come into the spotlight as fruitful producers of structurally diverse secondary metabolites, and remain relatively untapped. In this study, we sequenced 21 marine-derived actinomycete strains, rarely studied for their secondary metabolite potential and under-represented in current genomic databases. We found that genome size and phylogeny were good predictors of biosynthetic gene cluster diversity, with larger genomes rivalling the well-known marine producers in the Streptomyces and Salinispora genera. Genomes in the Micrococcineae suborder, however, had consistently the lowest number of biosynthetic gene clusters. By networking individual gene clusters into gene cluster families, we were able to computationally estimate the degree of novelty each genus contributed to the current sequence databases. Based on the similarity measures between all actinobacteria in the Joint Genome Institute's Atlas of Biosynthetic gene Clusters database, rare marine genera show a high degree of novelty and diversity, with Corynebacterium, Gordonia, Nocardiopsis, Saccharomonospora and Pseudonocardia genera representing the highest gene cluster diversity. This research validates that rare marine actinomycetes are important candidates for exploration, as they are relatively unstudied, and their relatives are historically rich in secondary metabolites.

2013
Becerril-Espinosa, A, Freel KC, Jensen PR, Soria-Mercado IE.  2013.  Marine Actinobacteria from the Gulf of California: diversity, abundance and secondary metabolite biosynthetic potential. Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology. 103:809-819.   10.1007/s10482-012-9863-3   AbstractWebsite

The Gulf of California is a coastal marine ecosystem characterized as having abundant biological resources and a high level of endemism. In this work we report the isolation and characterization of Actinobacteria from different sites in the western Gulf of California. We collected 126 sediment samples and isolated on average 3.1-38.3 Actinobacterial strains from each sample. Phylogenetic analysis of 136 strains identified them as members of the genera Actinomadura, Micromonospora, Nocardiopsis, Nonomuraea, Saccharomonospora, Salinispora, Streptomyces and Verrucosispora. These strains were grouped into 26-56 operational taxonomic units (OTUs) based on 16S rRNA gene sequence identities of 98-100 %. At 98 % sequence identity, three OTUs appear to represent new taxa while nine (35 %) have only been reported from marine environments. Sixty-three strains required seawater for growth. These fell into two OTUs at the 98 % identity level and include one that failed to produce aerial hyphae and was only distantly related (a parts per thousand currency sign95.5 % 16S identity) to any previously cultured Streptomyces sp. Phylogenetic analyses of ketosynthase domains associated with polyketide synthase genes revealed sequences that ranged from 55 to 99 % nucleotide identity to experimentally characterized biosynthetic pathways suggesting that some may be associated with the production of new secondary metabolites. These results indicate that marine sediments from the Gulf of California harbor diverse Actinobacterial taxa with the potential to produce new secondary metabolites.

Prieto-Davo, A, Villarreal-Gomez LJ, Forschner-Dancause S, Bull AT, Stach JEM, Smith DC, Rowley DC, Jensen PR.  2013.  Targeted search for actinomycetes from nearshore and deep-sea marine sediments. Fems Microbiology Ecology. 84:510-518.   10.1111/1574-6941.12082   AbstractWebsite

Sediment samples collected off the coast of San Diego were analyzed for actinomycete diversity using culture-independent techniques. Eight new operational taxonomic units (OTUs) in the Streptomycetaceae were identified as well as new diversity within previously cultured marine OTUs. Sequences belonging to the marine actinomycete genus Salinispora were also detected, despite the fact that this genus has only been reported from more tropical environments. Independent analyses of marine sediments from the Canary Basin (3814m) and the South Pacific Gyre (5126 and 5699m) also revealed Salinispora sequences providing further support for the occurrence of this genus in deep-sea sediments. Efforts to culture Salinispora spp. from these samples have yet to be successful. This is the first report of Salinispora spp. from marine sediments >1100m and suggests that the distribution of this genus is broader than previously believed.

2010
Jensen, PR.  2010.  Linking species concepts to natural product discovery in the post-genomic era. Journal of Industrial Microbiology & Biotechnology. 37:219-224.   10.1007/s10295-009-0683-z   AbstractWebsite

A widely accepted species concept for bacteria has yet to be established. As a result, species designations are inconsistently applied and tied to what can be considered arbitrary metrics. Increasing access to DNA sequence data and clear evidence that bacterial genomes are dynamic entities that include large numbers of horizontally acquired genes have added a new level of insight to the ongoing species concept debate. Despite uncertainties over how to apply species concepts to bacteria, there is clear evidence that sequence-based approaches can be used to resolve cohesive groups that maintain the properties of species. This cohesion is clearly evidenced in the genus Salinispora, where three species have been discerned despite very close relationships based on 16S rRNA sequence analysis. The major phenotypic differences among the three species are associated with secondary metabolite production, which occurs in species-specific patterns. These patterns are maintained on a global basis and provide evidence that secondary metabolites have important ecological functions. These patterns also suggest that an effective strategy for natural product discovery is to target the cultivation of new Salinispora taxa. Alternatively, bioinformatic analyses of biosynthetic genes provide opportunities to predict secondary metabolite novelty and reduce the redundant isolation of well-known metabolites. Although much remains to be learned about the evolutionary relationships among bacteria and how fundamental units of diversity can be resolved, genus and species descriptions remain the most effective method of scientific communication.

2008
Prieto-Davo, A, Fenical W, Jensen PR.  2008.  Comparative actinomycete diversity in marine sediments. Aquatic Microbial Ecology. 52:1-11.   10.3354/ame01211   AbstractWebsite

The diversity of cultured actinomycete bacteria was compared between near- and offshore marine sediments. Strains were tested for the effects of seawater on growth and analyzed for 16S rRNA gene sequence diversity. In total, 623 strains representing 6 families in the order Actinomycetales were cultured. These strains were binned into 16 to 63 operational taxonomic units (OTUs) over a range of 97 to 100 % sequence identity. The majority of the OTUs were closely related (> 98 % sequence identity) to strains previously reported from non-marine sources; indicating that most are not restricted to the sea. However, new OTUs averaged 96.6 % sequence identity with previously cultured strains and ca. one-third of the OTUs were marine-specific, suggesting that sediment communities include considerable actinomycete diversity that does not occur on land. Marine specificity did not increase at the off-shore sites, indicating high levels of terrestrial influence out to 125 km from shore. The requirement of seawater for growth was observed among < 6%. of the strains, while all members of 9 OTUs possessed this trait, revealing a high degree of marine adaptation among some lineages. Statistical analyses predicted greater OTU diversity at the off-shore sites and provided a rationale for expanded exploration of deep-sea samples. A change in community composition was observed, with the number of Micromonospora OTUs increasing in the off-shore samples. UniFrac (see http://bmf2.colorado.edu/unifrac) statistics support a difference in community composition between near- and off-shore locations. Overall, 123 of 176 strains had distinct 16S rRNA gene sequences, indicating a high level of actinomycete diversity in marine sediments.

2007
Gontang, EA, Fenical W, Jensen PR.  2007.  Phylogenetic diversity of gram-positive bacteria cultured from marine sediments. Applied and Environmental Microbiology. 73:3272-3282.   10.1128/aem.02811-06   AbstractWebsite

Major advances in our understanding of marine bacterial diversity have been gained through studies of bacterioplankton, the vast majority of which appear to be gram negative. Less effort has been devoted to studies of bacteria inhabiting marine sediments, yet there is evidence to suggest that gram-positive bacteria comprise a relatively large proportion of these communities. To further expand our understanding of the aerobic gram-positive bacteria present in tropical marine sediments, a culture-dependent approach was applied to sediments collected in the Republic of Palau from the intertidal zone to depths of 500 m. This investigation resulted in the isolation of 1,624 diverse gram-positive bacteria spanning 22 families, including many that appear to represent new taxa. Phylogenetic analysis of 189 representative isolates, based on 16S rRNA gene sequence data, indicated that 124 (65.6%) belonged to the class Actinobacteria while the remaining 65 (34.4%) were members of the class Bacilli. Using a sequence identity value of >= 98%, the 189 isolates grouped into 78 operational taxonomic units, of which 29 (37.2%) are likely to represent new taxa. The high degree of phylogenetic novelty observed during this study highlights the fact that a great deal remains to be learned about the diversity of gram-positive bacteria in marine sediments.

2006
Fenical, W, Jensen PR.  2006.  Developing a new resource for drug discovery: marine actinomycete bacteria. Nature Chemical Biology. 2:666-673.   10.1038/nchembio841   AbstractWebsite

Natural products are both a fundamental source of new chemical diversity and an integral component of today's pharmaceutical compendium. Yet interest in natural-product drug discovery has waned, in part owing to diminishing returns from traditional resources such as soil bacteria. The oceans cover 70% of the Earth's surface and harbor most of the planet's biodiversity. Although marine plants and invertebrates have received considerable attention as a resource for natural-product discovery, the microbiological component of this diversity remains relatively unexplored. Recent studies have revealed that select groups of marine actinomycetes are a robust source of new natural products. Members of the genus Salinispora have proven to be a particularly rich source of new chemical structures, including the potent proteasome inhibitor salinosporamide A, and other distinct groups are yielding new classes of terpenoids, amino acid-derived metabolites and polyene macrolides. The continued development of improved cultivation methods and technologies for accessing deep-sea environments promises to provide access to this significant new source of chemical diversity.