One of the greatest challenges facing modern medicine today is antibiotic resistance. Almost a century since Penicillin was first discovered in strains of mold, medical science has isolated thousands of defensive, antibiotic compounds from microbes. These bio-active microbial metabolites have been mass produced as antibiotics to help humans fight infections.

Because the human microbiome depends on commensal (friendly) microbes in order to function optimally, antibiotics pose new challenges to the long term health and sustainability of the vast network of friendly microorganisms that lives in the human gut. Modern day antibiotics, although typically effective in acute situations, are not a sustainable solution for long-term immunity and gut health. New research published in Frontiers in Microbiology finds that seaweed forests may hold the key to overcoming antibiotic resistance.

Microorganisms are firstly working for us, not against us

A common species of seaweed called Laminaria ochroleuca is a rich source of friendly bacteria that can help humans fight microbial resistance, while providing anticancer activity. This species of seaweed, also referred to as golden kelp, is loaded with gram-positive bacteria called actinobacteria.

Soil-based actinobacteria are currently used in the production of about 10,000 different antibiotics and were instrumental in the development of life saving antibiotics, vancomycin and rifamycin. Actinobacteria exhibit a wide spectrum of bioactive microbial metabolites that have evolved alongside several valuable biosynthetic gene clusters. Now, researchers are looking to the sea to find an entirely new constellation of actinobacteria and their secondary metabolites for the treatment of disease. One of the richest sources of these microbial medicines can be found in golden kelp.

Senior study author Dr. Maria de Fátima Carvalho of the Interdisciplinary Center of Marine and Environmental Research (CIIMAR), Portugal says that actinobacteria form spores and branched networks “just like a fungus.” However, these land-based secondary metabolites are “beginning to run out.” A richer source of bio-active microbial molecules still exists, in the under-explored marine phylum of actinobacteria. Each strain of actinobacteria contains the genetic instructions to produce between 15 and 25 secondary metabolites.

“Several novel drug leads derived from marine Actinobacteria are already known,” says Carvalho. “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.” These actinobacteria also reside on sponges, fish, mollusks, mangroves and sea sediments. In order to stay one step ahead of evolving pathogens, medical science must tap into the metabolites of sea-dwelling actinobacteria.

Forty-five new actinobacteria samples isolated from golden kelp, could help fight infections and certain cancers

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

The research team gathered a sample of Laminaria ochroleuca from a rocky shore in northern Portugal. For six weeks, the researchers cultured 90 strains of actinobacteria from the kelp sample. Two of the isolated strains could not be identified in the comprehensive international database of natural bio-active compounds. Exactly half of the microbial extracts (45 samples) halted the growth of Candida albicans, Staphylococcus aureaus, or both. The microbial extracts were effective against these pathogens at very low concentrations. Even more remarkably, seven of the actinobacteria extracts inhibited the growth of nerve cell cancers and breast cancers. The extracts did not harm non-cancerous cells, making them a viable candidate for the development of new immunotherapy drugs.

“This study reveals that the seaweed L. ochroleuca is a rich source of Actinobacteria with promising antimicrobial and anticancer activities,” sums up Carvalho.