Microalgal biomass offers a promising biofertilizer option due to its nutrient-rich composition, adaptability, and environmental benefits. This study evaluated the potential of microalgal-based biofertilizers—microalgal Chlorella biomass, de-oiled microalgal biomass (DMB), and de-oiled and de-aqueous extract microalgal biomass (DAEMB)—in enhancing lettuce growth, soil nutrient dynamics, and microbial community composition. Lettuce seedlings were cultivated with these biofertilizers, and plant growth parameters, photosynthetic pigments, and nitrogen uptake were assessed. Soil incubation experiments further examined nutrient mineralization rates, while DNA sequencing analyzed shifts in rhizosphere microbial communities. Lettuce grown with these biofertilizers exhibited improved growth parameters compared to controls, with Chlorella biomass achieving a 31.89% increase in shoot length, 27.98% in root length, and a 47.33% increase in fresh weight. Chlorophyll a and total chlorophyll levels increased significantly in all treatments, with the highest concentrations observed in the Chlorella biomass treatment. Soil mineralization studies revealed that DMB and DAEMB provided a gradual nitrogen release, while Chlorella biomass exhibited a rapid nutrient supply. Microbial community analyses revealed shifts in bacterial and fungal diversity, with increased abundance of nitrogen-fixing and nutrient-cycling taxa. Notably, fungal diversity was enriched in biomass and DAEMB treatments, enhancing soil health and reducing pathogenic fungi. These findings highlight microalgal biofertilizers’ potential to enhance soil fertility, plant health, and sustainable resource use in agriculture.

In recent years, researchers have turned their attention to the co-cultivation of microalgae and plants as a means to enhance the growth of hydroponically cultivated plants while concurrently producing microalgal biomass. However, the techniques used require precise calibration based on plant growth responses and their interactions with the environment and cultivation conditions. This study initially focused on examining the impact of hydroponic nutrient concentrations on the growth of the microalga Chlorella sp. AARL G049. The findings revealed that hydroponic nutrient solutions with electrical conductivities (EC) of 450 µS/cm and 900 µS/cm elicited a positive response in microalgae growth, resulting in high-quality biomass characterized by an elevated lipid content and favorable properties for renewable biodiesel. The biomass also exhibited high levels of polyunsaturated fatty acids (PUFAs), indicating excellent nutritional indices. The microalgae culture and microalgae-free culture, along with inoculation-free lettuce (Lactuca sativa L. var. longifolia) and lettuce that was inoculated with plant growth actinobacteria, specifically the actinomycete Streptomyces thermocarboxydus S3, were subsequently integrated into a hydroponic deep-water culture system. The results indicated that several growth parameters of lettuce cultivated in treatments incorporating microalgae experienced a reduction of approximately 50% compared to treatments without microalgae, and lowering EC levels in the nutrient solution from 900 µS/cm to 450 µS/cm resulted in a similar approximately 50% reduction in lettuce growth. Nevertheless, the adverse impacts of microalgae and nutrient stress were alleviated through the inoculation with actinomycetes. Even though the co-cultivation system leads to reduced lettuce growth, the system enables the production of high-value microalgal biomass with exceptional biodiesel fuel properties, including superior oxidative stability (>13 h), a commendable cetane number (>62), and a high heating value (>40 MJ/kg). This biomass, with its potential as a renewable biodiesel feedstock, has the capacity to augment the overall profitability of the process. Hence, the co-cultivation of microalgae and actinomycete-inoculated lettuce appears to be a viable approach not only for hydroponic lettuce cultivation but also for the generation of microalgal biomass with potential applications in renewable energy.

Harmful algal blooms impact human welfare and are a global concern. Sargassum spp., a type of algae or seaweed that can potentially bloom in certain regions of the sea around Thailand, exhibits a noteworthy electron capacity as the sole reducing and stabilizing agent, which suggests its potential for mediating nanoparticle composites. This study proposes an eco-friendly microwave-assisted biosynthesis (MAS) method to fabricate silver nanoparticles coated with Sargassum aqueous extract (Ag/AgCl-NPs-ME). Ag/AgCl-NPs-ME were successfully synthesized in 1 min using a 20 mM AgNO₃ solution without additional hazardous chemicals. UV–visible spectroscopy confirmed their formation through a surface plasmon resonance band at 400–500 nm. XRD and FTIR analyses verified their crystalline nature and involvement of organic molecules. TEM and SEM characterization showed well-dispersed Ag/AgCl-NPs-ME with an average size of 36.43 nm. The EDS results confirmed the presence of metallic Ag⁺ and Cl⁻ ions. Ag/AgCl-NPs-ME exhibited significant antioxidant activity against free radicals (DPPH, ABTS, and FRAP), suggesting their effectiveness. They also inhibited enzymes (tyrosinase and ACE) linked to diseases, indicating therapeutic potential. Importantly, the Ag/AgCl-NPs-ME displayed remarkable cytotoxicity against cancer cells (A375, A549, and Caco-2) while remaining non-toxic to normal cells. DNA ladder and TUNEL assays confirmed the activation of apoptosis mechanisms in cancer cells after a 48 h treatment. These findings highlight the versatile applications of Ag/AgCl-NPs-ME in food, cosmetics, pharmaceuticals, and nutraceuticals.