Sep 10, 2007

From Aladdin’s Cave to Treasure Island

For a long time, it was thought that the land of actinomycetes was... well, land. I mean, they were supposed to be terrestrial creatures, even although some of them were isolated from samples taken in sea habitats (for instance, read this article from 1958). But these "marine" bacteria, generally found in shallow waters, were quite similar to their counterparts from land. For this reason, it was assumed that any actinomycetes obtained from the sea were just wash-offs from the shore.

Now this view is changing. But how can we say if a microbe isolated from a particular sea location is a true neighbor on the block (as opposed to be just derived from a passing-by or dormant spore, coming from land)? Ideally, it should be recognized by the following criteria: its ability to grow optimally at native conditions (salinity, pressure, temperature, nutrients); demonstration that the organism is really active on location; and the recognition of particular metabolic profiles, not found in terrestrial relatives. Nowadays, the existence of truly marine actinomycetes seems to be supported by solid data.

Similarly to their terrestrial relatives, marine microbes are a rich source of bioactive metabolites (antibiotics, antitumor drugs) and enzymes with different applications. For instance, cultivation of a marine actinomycete known as Salinispora tropica yielded a number of novel metabolites, not found before. One of these compounds, salinosporamide A, has antitumor properties and is currently being tested in humans for the treatment of cancer. Sequencing the genome of Salinispora tropica unveiled a number of genes coding for the synthesis of 17 potential metabolites; most of these compounds had not been detected in previous culturing of the microbe. Then, the researchers used the genetic information to guide a new chemical analysis of Salinispora cultures. The analysis uncovered an additional, novel compound (salinilactam), which had a structure corresponding to that deduced from the DNA sequence.

Let me finish with David Hopwood's words from Therapeutic treasures from the deep:

"In a recent book I likened the plethora of previously unknown genes in a newly sequenced Streptomyces genome to an Aladdin's Cave. Perhaps Treasure Island would be a more apt metaphor in this case [Salinispora]"


List of links:
- Article from 1958: Grein A, Meyers SP, Growth characteristics and antibiotic production of actinomycetes isolated from littoral sediments and materials suspended in sea water. J. Bacteriol. 1958, 76, 457-463.
- Marine actinomycetes: Bull AT, Stach JE, Ward AC, Goodfellow M, Marine actinobacteria: perspectives, challenges, future directions. Antonie Van Leeuwenhoek, 2005, 87, 65-79.
- Salinosporamide A: Wikipedia.
- Sequencing the genome of Salinispora tropica: Udwary DW, Zeigler L, Asolkar RN, Singan V, Lapidus A, Fenical W, Jensen PR, Moore BS, Genome sequencing reveals complex secondary metabolome in the marine actinomycete Salinispora tropica. Proc. Natl. Acad. Sci. USA, 2007 , 104, 10376-10381.
- Therapeutic treasures from the deep: Hopwood DA, Nat. Chem. Biol. 2007, 3, 457-458.
- Aladdin's Cave: Aladdin - Wikipedia.
- Treasure Island: Wikipedia.

Left, Aladdin in the Magic Garden, an illustration by Max Liebert for Ludwig Fulda's Aladin und die Wunderlampe. Source: Wikipedia.
Right, Jim Hawkins and the treasure of Treasure Island, an illustration by Georges Roux for the 1885 edition of Treasure Island by Robert Louis Stevenson. Source: Wikipedia.

This post is my contribution to Microbial Week, a collection of posts highlighting the many roles of microbes in deep-sea or marine environments. The event is organized by Christina Kellogg and the guys at Deep-Sea News.

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