Microbiology Research Journal International

Examining the Function of Metabolites Generated from Cyanobacteria as Antimicrobial Agents from a 21st-Century Perspective

2026-07-09T12:51:18+00:00

Cyanobacteria are among the oldest oxygenic photosynthetic organisms on Earth and occupy an extraordinarily broad range of ecological niches, from marine and freshwater systems to extreme terrestrial habitats. Their capacity to withstand intense ultraviolet radiation, desiccation, nutrient scarcity and microbial competition is underpinned by a rich biosynthetic repertoire of secondary metabolites, many of which display potent antibacterial, antifungal and antiviral activities. This review examines the chemical diversity, biosynthetic origin and mechanisms of action of cyanobacterial antimicrobial metabolites, situating the discussion within the contemporary crisis of antimicrobial resistance and the stagnation of conventional antibiotic discovery pipelines. Cyclic and linear peptides, alkaloids, polyketides, macrolides, lipids and lectins isolated predominantly from filamentous genera such as Nostoc, Lyngbya, Moorea, Fischerella, Calothrix and Anabaena are discussed with reference to their molecular targets, which include bacterial RNA polymerase, fungal ergosterol-rich membranes, viral envelope glycoproteins and components of the bacterial cell wall and electron transport chain. The contribution of non-ribosomal peptide synthetase and polyketide synthase gene clusters to this chemical diversity is examined alongside genome-mining approaches that have accelerated the discovery of cryptic biosynthetic pathways. Biotechnological obstacles to translating laboratory findings into clinically usable agents, including low and inconsistent yields, cultivation scale-up difficulties, structural complexity and the toxicological profile of certain cyanobacterial metabolites, are critically appraised, together with emerging nanoformulation strategies intended to overcome bioavailability constraints. The review concludes that cyanobacteria represent a comparatively underexploited reservoir of structurally novel antimicrobial chemotypes that merit sustained, mechanistically grounded investigation, while acknowledging that translational progress remains constrained by supply, safety and regulatory hurdles that have yet to be systematically resolved.

Antimicrobial Profiling of Selected Medicinal Plants from West Pokot, Kenya: Plant Parts and Concentration-Specific Effects

2026-07-02T05:49:28+00:00

Antimicrobial resistance has increased interest in evaluating medicinal plants as potential sources of bioactive compounds. This study evaluated the antibacterial and antifungal activities of selected medicinal plants from West Pokot County, Kenya, and determined the effects of plant part and extract concentration on antimicrobial activity. Leaf, stem bark, and root extracts of Lannea fulva, Ochna insculpta, Pittosporum viridiflorum, Schrebera alata, and Teclea pilosa were evaluated against four bacterial pathogens (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus cereus) and two fungal pathogens (Aspergillus fumigatus and Candida albicans). Antimicrobial activity was assessed using agar diffusion methods, with ciprofloxacin and amphotericin B as positive controls and dimethyl sulfoxide as the negative control. Data were analyzed using factorial analysis of variance, and mean separation was performed at p ≤ 0.05. The results showed that antimicrobial activity varied significantly with plant species, plant part, extract concentration, and microbial strain. Root extracts demonstrated higher antibacterial activity (mean inhibition zone = 10.773 mm) compared with leaf (9.936 mm) and stem bark extracts (9.241 mm). Among the crude extracts, Pittosporum viridiflorum root extract recorded the highest antibacterial activity in the plant-part comparison, producing an inhibition zone of 16.694 mm against E. coli. In concentration-based assays, P. viridiflorum root extract showed the highest antibacterial response against E. coli (22.11 mm) at 100% concentration. Antifungal activity differed significantly among plant species, plant parts, and concentrations. The highest antifungal activity among plant extracts was recorded in Schrebera alata root extract against A. fumigatus, producing an inhibition zone of 14.422 mm at 125% concentration. Amphotericin B produced the highest overall inhibition against fungal pathogens (15.081–16.057 mm), whereas dimethyl sulfoxide showed no meaningful activity (3.000 mm). The findings demonstrate that selected medicinal plants from West Pokot possess measurable antibacterial and antifungal properties, with clear plant part and concentration-dependent variations. Further phytochemical characterization, minimum inhibitory concentration determination, and toxicity evaluation are recommended before therapeutic application.

Effect of Biofertilization with a Mixture of Arbuscular Mycorrhizal Fungi and Natural Phosphate from Tilemsi on the Growth and Grain Yield of Sorghum (Sorghum bicolor L. Moench) in the Field in Koumantou

2026-07-03T13:50:26+00:00

Sorghum is an important food-security crop in Mali, but productivity is often constrained by poor soil fertility, particularly low phosphorus availability. Arbuscular mycorrhizal fungi and locally available natural phosphate may provide an alternative or complementary approach to mineral fertilisation. This study evaluated the effect of biofertilisation with a mixture of arbuscular mycorrhizal fungi and Tilemsi natural phosphate on sorghum growth and grain yield under field conditions in Koumantou, Bougouni region, Mali. The experiment used a randomised block design with five treatments and four replications: an uninoculated and unfertilised control, mineral fertiliser, Tilemsi natural phosphate, arbuscular mycorrhizal fungal inoculum, and the inoculum combined with Tilemsi natural phosphate. The fungal inoculum comprised Rhizophagus irregulare, Glomus aggregatum, and Glomus mosseae. Plant height and stem diameter were measured during growth, while panicle length, panicle weight, dry aboveground biomass, grain yield, and 1000-grain weight were assessed at harvest. The experimental soil was acidic and low in organic matter, nitrogen, potassium, and available phosphorus. Fertilised and inoculated treatments generally improved growth compared with the control. At 100 days after emergence, plant height ranged from 195.06 cm in the control to 216.28 cm under mineral fertiliser; the combined treatment reached 214.03 cm. Dry aboveground biomass was highest under the combined treatment (39.31 g) compared with the control (22.44 g). Grain yield was also numerically higher under the combined treatment than under the control. These findings suggest that arbuscular mycorrhizal fungi combined with Tilemsi natural phosphate may support sorghum growth in phosphorus-poor field conditions.

Antibacterial, Bactericidal and Membrane-Disruptive Activities of Essential Oils from Callistemon salignus, Croton gratissimus and Melaleuca bracteata against Reference Enterococcus Species

2026-07-09T12:55:43+00:00

The increasing occurrence of antimicrobial-resistant Enterococcus species has encouraged the investigation of plant-derived products with antibacterial potential. This study evaluated the antibacterial, bactericidal, and membrane-disruptive activities of essential oils obtained from the leaves of Callistemon salignus, Croton gratissimus, and Melaleuca bracteata against five reference Enterococcus species: Enterococcus avium, Enterococcus casseliflavus, Enterococcus hirae, Enterococcus gallinarum, and Enterococcus faecalis. Antibacterial activity was assessed by agar disc diffusion, while minimum inhibitory concentration and minimum bactericidal concentration values were determined using broth microdilution-based methods. Bactericidal potential was further interpreted using MBC/MIC ratios, and membrane-disruptive activity was evaluated using membrane-damage indices. All tested essential oils produced measurable inhibition against at least some of the Enterococcus species, with inhibition zones ranging from 9.0 to 12.0 mm, compared with 25 to 47 mm for ciprofloxacin. Melaleuca bracteata essential oil showed the strongest overall activity, with MIC values ranging from 2.5 to 5.0 mg/mL and MBC values of 5.0 to >5.0 mg/mL. Callistemon salignus showed moderate activity, with MIC values from 2.5 to >5.0 mg/mL and MBC values of 5.0 to >5.0 mg/mL. Croton gratissimus showed comparatively weaker activity, with MIC values of 5.0 to >5.0 mg/mL and no detectable bactericidal activity within the tested concentration range. Membrane-damage indices were highest for M. bracteata against E. avium and E. faecalis. Overall, the findings indicate that M. bracteata and C. salignus possess measurable antibacterial effects against reference Enterococcus species, with membrane disruption likely contributing to their activity.