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.

The consumption of lettuce is associated with an increased risk of ingesting nitrate, a naturally occurring and potentially harmful compound that can have adverse effects on human health. Hydroponic cultivation systems serve as effective tools for regulating nutrient solutions and nitrogen availability, which are essential for controlling nitrate levels. However, the techniques for reducing nutrient levels need to be appropriately calibrated based on lettuce growth responses and their interactions with the environment and growing conditions. Previous studies have demonstrated that plant probiotic actinomycetes can alleviate nutritional stress in various crops. However, there is a noticeable gap in research concerning the effects of actinomycetes on hydroponically grown lettuce, particularly under nutrient-limiting conditions. This study aimed to evaluate the effectiveness of the actinomycete Streptomyces thermocarboxydus S3 in enhancing lettuce growth in a nutrient-restricted hydroponic system. The results indicated that the detrimental effects of nutrient stress on lettuce were mitigated by the inoculation of lettuce with S. thermocarboxydus S3. This mitigation was evident in various growth parameters, including leaf count, shoot length, and the fresh and dry weights of both shoots and roots. In the presence of nutritional stress, S. thermocarboxydus S3 likely mitigated the negative effects on lettuce by reducing hydrogen peroxide levels, presumably through the synthesis of H₂O₂-scavenging enzymes. Furthermore, S. thermocarboxydus S3 successfully survived and colonized lettuce roots. Therefore, the inoculation of lettuce with S. thermocarboxydus S3 offers significant advantages for promoting lettuce growth in nutrient-limited hydroponic systems.

The development of sustainable microbial inoculants for crop production requires strains with demonstrated plant growth-promoting performance and well-characterized functional potential. This study evaluated the effect of Priestia sp. RMT2NF4, isolated from the rice rhizosphere, on sweet corn (Zea mays L.) seed physiological quality and early seedling vigor, supported by whole-genome sequencing analysis. Seed treatment effects were evaluated using a between-paper germination assay under controlled conditions at 25 °C for 7 days. Seed treatment with RMT2NF4 significantly increased germination percentage, germination index, and seedling growth rate by 13.26%, 21.30%, and 23.71%, respectively (p < 0.05). Inoculated seedlings also exhibited significantly greater shoot length, while root length and abnormal seedling proportion showed numerical but non-significant improvements. Genomic analysis identified genes putatively associated with tryptophan biosynthesis, nutrient acquisition, and stress adaptation. The integration of phenotypic validation and genome-informed functional profiling highlights the potential of RMT2NF4 and provides a basis for further evaluation of RMT2NF4 as a candidate plant growth-promoting bacterium to support sustainable sweet corn production and reduce reliance on chemical inputs.

Spent mushroom substrate (SMS), a lignocellulosic by-product of mushroom cultivation, represents a promising renewable carrier for microbial bioinoculants as well as agricultural waste valorization. This study evaluated SMS as a carrier for the plant growth-promoting actinobacterium Streptomyces gardneri MC1-2 and assessed its effects on tomato growth and soil bacterial communities. Three formulations were prepared: SMS alone (F1), SMS supplemented with 1% (w/w) carboxymethyl cellulose (CMC) (F2), and talc supplemented with 1% CMC and 1.5% CaCO₃ (F3). S. gardneri MC1-2 exhibited in vitro traits commonly associated with plant-beneficial activity, including indolic compound production, siderophore production, and inorganic phosphate solubilization. During 30 days of storage at 4, 30, and 40 °C, both SMS-based formulations maintained viable populations at a 3 Log CFU reduction, whereas the talc-based formulation lost viability within seven days. Among the formulations, F2 showed the best overall performance and was selected for the pot experiment. Direct inoculation with S. gardneri MC1-2 promoted tomato growth comparably to chemical fertilizer, while F2 strongly supported growth in sterile soil, where S. gardneri MC1-2 established and dominated the bacterial community. In non-sterile soil, reduced bacterial establishment suggested that competition with native microbiota limited inoculant performance. These findings demonstrate that SMS can serve as an effective carrier for Streptomyces-based bioinoculants with potential applications for sustainable crop production.