Defensive compounds produced by microbes are an important source of antibiotics and other medicines. However, in light of the increasing resistant microbes, researchers are taking their search for drug candidates offshore. A new study published in Frontiers in Microbiology reported that a common species of seaweed, Laminaria ochroleuca, is a rich source of bacteria with antimicrobial and anticancer activities, as well as potential new drug candidates.
"About half of the 20,000+ microbe-derived drug candidates currently known come from Actinobacteria," says researcher Maria de Fátima Carvalho from the Interdisciplinary Centre of Marine and Environmental Research (CIIMAR) in 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."
They are relatively unexplored but marine Actinobacteria are a rich source of bioactive microbial molecules. "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."
Predominantly found in sediments on the sea floor, Actinobacteria can also live inside other organisms that live and feed there. "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 characterised the Actinobacteria that live inside L. ochroleuca."
Carvalho's team analysed a sample of L. ochroleuca from a rocky shore off northern Portugal. Following six weeks of culture in the lab, researchers isolated 90 Actinobacterial strains from the sample, which were then screened for antimicrobial and anticancer activity.
"45 of the Actinobacterial extracts inhibited growth of Candida albicans, Staphylococcus aureus, or both," says Carvalho.
Some extracts were active against common pathogens even at low concentrations, making them promising candidates for the discovery of antimicrobial drugs. A number of them also showed selective anticancer activity. The team are keen to take this work forward in their future research.