As antimicrobial resistance continues to outpace the development of new antibiotics, scientists are turning to an unlikely and abundant source of chemical innovation: seaweed. A comprehensive new review published in Discover Biotechnology argues that the secondary metabolites produced by marine macroalgae—compounds refined by millions of years of chemical warfare in the ocean—represent one of the most promising untapped reservoirs for next-generation microecological therapeutics. Written by Aravinth Annamalai and Prabhu Kolandhasamy of the Saveetha Institute of Medical and Technical Sciences in Chennai, India, the review synthesises evidence spanning natural product chemistry, microbial ecology and translational pharmacology, and makes the case that brown, red and green algae can yield molecules that both kill drug-resistant pathogens and reshape the human microbiome in medically meaningful ways.
The chemical arsenal on display is remarkable in its diversity. Brown algae of the class Phaeophyceae are dominated by phlorotannins, polyphenolic polymers built from phloroglucinol units and linked through ether, phenyl and dibenzodioxin bonds. The degree of polymerisation governs both solubility and bioactivity, and roughly 220 phlorotannin entries are catalogued in the Seaweed Metabolite Database. Red algae, which show the highest fingerprint diversity in that database with 645 recorded metabolites, specialise in sulfated galactans such as carrageenans and in an extraordinary array of halogenated terpenes and acetogenins, exemplified by compounds like elatol and isolaurinterol from the genus Laurencia. Laurencia dendroidea alone has yielded more than 40 unique terpenoids, supported by 21 identified terpene synthase genes. Green algae contribute sulfated polysaccharides known as ulvans, alongside specialised peptides with emerging biomedical relevance.
The antimicrobial mechanisms underlying these compounds are mechanistically distinct from those of classical antibiotics, which is precisely what makes them attractive in an era of multidrug resistance. Phlorotannins act through a combination of membrane disruption, chelation of essential metal ions and the generation of oxidative stress, while simultaneously interfering with quorum sensing—the chemical communication system bacteria use to coordinate virulence factor production and biofilm formation. Studies of phlorotannins from Hizikia fusiforme, for example, demonstrated both antimicrobial and anti-quorum-sensing activity. Halogenated terpenoids from Laurencia species show potent activity against Staphylococcus aureus and Vibrio species, an effect attributed to their lipophilic and electrophilic chemical character. Sulfated polysaccharides such as carrageenan and fucoidan take a different tack, interfering with bacterial adhesion and colonisation by altering electrostatic interactions at the microbial cell surface. Because these molecules hit multiple cellular targets at once, the risk of resistance emergence may be inherently lower than for single-target drugs.
The antiviral and antifungal records of these metabolites are equally striking. Sulfated polysaccharides including carrageenans and agars can mimic host cell receptors, preventing enveloped viruses from attaching to and entering target cells, while phlorotannins inhibit viral proteases and polymerases by binding to key viral proteins; a phlorotannin-rich extract of Ascophyllum nodosum has been shown to inhibit influenza infection. Against fungi, phlorotannins compromise cell wall integrity and block ergosterol biosynthesis—pathways reminiscent of synthetic antifungals but potentially less prone to resistance—while elatol exerts fungicidal effects through membrane disruption and oxidative stress. Antiparasitic activity has been traced to fatty acid derivatives and phenolic compounds that interfere with parasite metabolism and membrane stability. The review notes, however, that most of this evidence remains in vitro, and that in vivo validation in relevant animal models is urgently needed before clinical deployment.
Beyond direct pathogen killing, the most transformative dimension of the review concerns microbiome engineering. Seaweed-derived polysaccharides such as fucoidans, laminarins and ulvans act as selective prebiotics, enriching beneficial taxa such as Bifidobacterium, Lactobacillus and Akkermansia while suppressing opportunistic members of the Bacteroidetes and Proteobacteria. In broiler chickens, dietary inclusion of 5 to 10 grams per kilogram of seaweed polysaccharides improved intestinal architecture, microbial balance and weight gain in a dose-dependent manner. In pre-weaning Holstein calves, seaweed polysaccharide supplementation increased the abundance of Prevotella and Succiniclasticum, reduced diarrhoea incidence, lowered systemic inflammatory markers including IL-18, TNF-α and IFN-γ, and elevated immune effectors such as complement C3 and IgM. These effects were linked to increased abundance of gut microbes involved in alkaloid and glucocorticoid biosynthesis, suggesting a coordinated immunometabolic mechanism.
The ecological sophistication of these interactions extends to the seaweeds themselves, which the authors describe as holobionts—integrated units of alga plus microbiota. Macroalgae such as Agarophyton vermiculophyllum engage in what researchers call chemically mediated microbial gardening, dynamically attracting symbiotic microbes and excluding pathogens depending on environmental conditions like salinity. Exometabolomic analyses show that macroalgae release distinctive nitrogenous and lipid-rich compounds that support microbial colonisation and nutrient cycling, and genomic surveys have identified more than 4,400 polysaccharide utilisation loci and roughly 8,800 biosynthetic gene clusters in algae-associated bacteria—clear evidence of co-evolutionary adaptation for metabolising algal substrates. Many metabolites previously credited to seaweeds are in fact synthesised or chemically modified by their associated microbiota, a realisation that reshapes how such compounds should be discovered, sourced and standardised.
Biotechnology is now converging to solve the longstanding problems that have kept these compounds out of the clinic. On the extraction side, green technologies—ultrasound-assisted extraction, microwave-assisted extraction, supercritical fluid extraction and enzymatic hydrolysis—are replacing crude solvent methods, improving yield, selectivity and sustainability. Natural deep eutectic solvents optimised for Fucus vesiculosus have delivered high-purity phlorotannins validated by HPLC-MS profiling. Nanotechnology offers solutions to the chronic bioavailability problem: red seaweed-derived nanoparticles provide biocompatibility and controlled release, while silver-based metal–organic frameworks embedded in κ-carrageenan hydrogels combine antibacterial action with the mechanical properties needed for wound dressings. One carrageenan–silver hydrogel composite has already entered commercial wound-healing use, and fucoidan–chitosan nanoparticles are in Phase I trials for targeted colorectal delivery of curcumin.
Synthetic biology is arguably the most ambitious frontier. Metagenomic mining of seaweed microbiota has illuminated vast biosynthetic potential in genera such as Pseudoalteromonas and Vibrio, and CRISPR-based editing combined with heterologous expression in fast-growing chassis like Vibrio natriegens is enabling high-yield biosynthesis of halogenated meroterpenes. The red algal lectin Griffithsin, produced by expression in Nicotiana benthamiana plants, has achieved preclinical validation as a topical antiviral microbicide, demonstrating industrial scalability. Bioinformatic platforms such as antiSMASH and BiG-SCAPE are accelerating the annotation of novel gene clusters encoding alkaloids, terpenoids and glycosides. On the regulatory side, the strongest proof of concept remains sodium oligomannate (GV-971), an oligosaccharide derived from marine algae that received conditional approval in China for Alzheimer’s disease following a 36-week Phase 3 trial—although the review stresses that broader global endorsement awaits more extensive chronic toxicity data.
The authors are candid about the obstacles that remain. Metabolite composition varies with season, geography, salinity, light and harvest conditions; the antimicrobial activity of Ulva lactuca extracts, remarkably, fluctuates with lunar phase at harvest. Poor oral bioavailability, low gastrointestinal stability, first-pass hepatic metabolism and batch-to-batch inconsistency in crude extracts complicate pharmacokinetic modelling and regulatory approval. Structural heterogeneity in fucoidans—where sulfation patterns and molecular weight determine bioactivity—means that harmonised analytical standards are lacking. The review calls for omics-guided bioactivity mapping, standardised extraction and assay protocols, microbiome-informed therapeutic design, and sustainable cultivation systems including land-based aquaculture and integrated multi-trophic approaches that recycle nutrients by pairing seaweed farming with fish or shellfish production. Photobioreactors and controlled tank cultures, in which salinity, light and nutrient stress can be tuned to boost production of phlorotannins, fucoidan and terpenoids, offer a path to reproducible, quality-controlled biomass.
Taken together, the evidence assembled in this review paints seaweed-derived secondary metabolites as far more than a curiosity of marine natural product chemistry. They are multimodal antimicrobials capable of attacking pathogens through mechanisms that bypass existing resistance determinants; they are prebiotic scaffolds that can rebuild dysbiotic microbial communities and dampen inflammation; and they are scaffolds for nanocarriers and synthetic biology platforms that are already reaching commercial and clinical milestones. What is needed now, the authors conclude, is interdisciplinary alignment—marine biotechnologists, pharmacologists, microbial ecologists and clinicians working within shared analytical frameworks—to convert a chemically extraordinary ocean resource into dependable, evidence-based medicines for the microbiome-centred era of healthcare.
The timing of this review reflects a broader shift in how antimicrobial research is conceptualised. Rather than seeking single molecules that sterilise microbial communities, the microecological approach emphasises selective modulation—suppressing pathogens while preserving or even enriching commensal taxa. Seaweed metabolites are unusually well suited to this paradigm because their activities span both direct antimicrobial action and substrate-level nutrition of beneficial bacteria, a dual function rarely seen in conventional small-molecule antibiotics.
The taxonomic partitioning of metabolite classes among algal phyla is itself scientifically informative. The distinct biosynthetic capabilities of Phaeophyceae, Rhodophyta and Chlorophyta mean that sourcing decisions can be guided by target compound class: phlorotannins from brown algae for antioxidant and anti-quorum-sensing applications, carrageenans and halogenated terpenoids from red algae for antiviral and antibacterial purposes, and ulvans from green algae for prebiotic formulations. This phylum-specific specialisation, catalogued in resources such as the Seaweed Metabolite Database, provides a rational framework for bioprospecting programmes.
The open-access status of the review, published as volume 3, article number 7 of Discover Biotechnology, makes the full catalogue of compound classes, mechanisms and translational case studies freely available to researchers in regions where seaweed cultivation is already an established industry. The authors’ citation record, with the article already accumulating citations and thousands of accesses within weeks of publication, suggests substantial interest in microbiome-centred alternatives to conventional antibiotics. As regulatory agencies increasingly grapple with how to evaluate complex, heterogeneous natural products, the standardisation agenda outlined by Annamalai and Kolandhasamy may prove as consequential as the molecules themselves.
Subject of Research: Bioactive secondary metabolites from marine macroalgae for antimicrobial action and microbiome modulation
Article Title: Marine macroalgal metabolites in microbial modulation for next-generation microecological therapeutics
Article References: Annamalai, A., & Kolandhasamy, P. (2026). Marine macroalgal metabolites in microbial modulation for next-generation microecological therapeutics. Discover Biotechnology, 3(1), Article 7. https://doi.org/10.1007/s44340-025-00047-6
Image Credits: AI Generated
DOI: 10.1007/s44340-025-00047-6
Keywords: marine macroalgae, seaweed metabolites, antimicrobial resistance, phlorotannins, sulfated polysaccharides, fucoidan, carrageenan, microbiome modulation, prebiotics, synthetic biology, nanocarriers, microecological therapeutics
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Morgan Morrow. (September 10, 2026). Seaweed Metabolites Could Power the Next Wave of Microbiome Medicine. Scienmag. https://scienmag.com/seaweed-metabolites-could-power-the-next-wave-of-microbiome-medicine/
Morgan Morrow. “Seaweed Metabolites Could Power the Next Wave of Microbiome Medicine.” Scienmag, 10 September 2026, https://scienmag.com/seaweed-metabolites-could-power-the-next-wave-of-microbiome-medicine/. Accessed 10 September 2026.
Morgan Morrow. “Seaweed Metabolites Could Power the Next Wave of Microbiome Medicine.” Scienmag. September 10, 2026. https://scienmag.com/seaweed-metabolites-could-power-the-next-wave-of-microbiome-medicine/
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