Just as seaweed-clad characters in The Tempest obeyed the commands of a vengeful sorcerer, seaweed-dwelling bacteria may realize the biotechnological and pharmacological designs of scientists who are intent on overcoming drug resistance. One seaweed in particular, the macroalgae Laminaria ochroleuca, has been found to contain cultivable Actinobacteria that show promising antimicrobial and anticancer activities.

The finding appeared April 9 in the journal Frontiers in Microbiology, in an article titled, “Actinobacteria Isolated from Laminaria ochroleuca: A Source of New Bioactive Compounds.” The article describes how the seaweed, which was harvested from a rocky shore in northern Portugal, was processed to yield actinobacterial strains, which were then tested for antibacterial and anticancer activity.

“About half of the 20,000+ microbe-derived drug candidates currently known come from Actinobacteria,” said Maria de Fátima Carvalho, a researcher at the Interdisciplinary Center of Marine and Environmental Research (CIIMAR), Portugal. “Now the supply of new species on land—where they form spores and branched networks just like a fungus—is beginning to run out.”

In the sea, Actinobacteria is found predominantly in sediments on the sea floor, but it can also live inside other organisms that live and feed there—including brown algae (seaweed).

“Several novel drug leads derived from marine Actinobacteria are already known,” noted Carvalho, the senior author of the current study. “These include anticancer agent salinosporamide A, currently in clinical trials, and several new antibiotics that are effective against drug-resistant infections like MRSA and tuberculosis.”

“The brown alga L. ochroleuca forms complex structures called kelp forests, which are among the most diverse and productive ecosystems in the world,” continued Carvalho. “But until now, no-one had characterized the Actinobacteria that live inside L. ochroleuca.”

In other kelp species, Actinobacteria are known to provide protective compounds in exchange for nutrients and shelter, which could be a source of new drug candidates.

“After six weeks of culture in the lab, we isolated 90 Actinobacterial strains from the sample,” Carvalho explained. Extracts from these Actinobacteria were then screened for antimicrobial and anticancer activity.

“Forty-five isolates inhibited the growth of Candida albicans and/or Staphylococcus aureus, with MIC values ranging from <0.5 to 1000 μg mL−1. The actinobacterial isolates were also tested for their anticancer potential on two human cancer cell lines,” the authors of the current study indicated. “Twenty-eight extracts affected the viability of at least one human cancer cell line (breast carcinoma T-47D and neuroblastoma SH-SY5Y) and non-carcinogenic endothelial cell line (hCMEC/D3).”

Some extracts were active against these common pathogens even at extremely low concentrations, making them promising candidates for the discovery of antimicrobial drugs. Several also showed selective anticancer activity.

“Seven of the extracts inhibited growth of breast and particularly nerve cell cancers, while having no effect on noncancer cells,” Carvalho emphasized. “This study reveals that the seaweed L. ochroleuca is a rich source of Actinobacteria with promising antimicrobial and anticancer activities.”

Further tests on the most potent of these strains revealed that some of the effects are likely the result of newly discovered compounds.

“We identified extracts from two Actinobacteria strains that do not match any known compounds in the most comprehensive international database of natural bioactive compounds,” Carvalho added. “We intend to follow up on these exciting results.”

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