Eutrophication facilitates the proliferation of cyanobacteria, ultimately leading to the formation of harmful cyanobacterial blooms. Prodigiosin, known for its algicidal properties, presents significant potential for application in water pollution remediation. This study aims to identify and characterize a novel strain with superior prodigiosin production capabilities and to elucidate the algicidal mechanism of prodigiosin against Microcystis aeruginosa and Anabaena sp. by assessing the photosynthetic responses of algal cells in the presence of prodigiosin. The findings revealed the isolation and identification of a new strain, ZC52, classified as Serratia marcescens. The optimal medium composition was determined to be 20.0 mL·L⁻¹ glycerol, 15.0 g·L⁻¹ beef bone peptone, 15.0 g·L⁻¹ magnesium sulfate heptahydrate, 0.15 g·L⁻¹ corn dry powder, and 0.250% tyrosine, resulting in a 47.40% increase in prodigiosin yield, thereby achieving a production level of 7.644 g·L⁻¹. Moreover, the algicidal activity exhibited a concentration-dependent relationship, with 10.0 mg·L⁻¹ of prodigiosin leading to approximately 53.25% and 30.44% inhibition of chlorophyll a content within 24 h, demonstrating the potential of prodigiosin as an effective algicidal compound. Meanwhile, exposure to 10.0 mg·L⁻¹ of prodigiosin resulted in reductions of 46.88% and 21.02% in the Fv/Fm values of M. aeruginosa and Anabaena sp., respectively. Our results indicated that prodigiosin can inhibit the accumulation of photosynthetic pigments and significantly diminish algal photosynthetic efficiency. This study not only identifies valuable microbial resources for prodigiosin production but also provides a theoretical framework and empirical evidence to support the scientific management of cyanobacterial blooms.

Beauveria bassiana is one of the most widely used entomopathogenic fungi in insect pest management, and the need for rapid and reproducible quantification of fungal conidia to monitor process performance and to quality control products during biopesticide production is imperative. Conventional methodologies, such as hemocytometer counting and plate dilution assays, are time consuming, laborious and subject to significant operator-to-operator variability. Although optical methods have been increasingly explored for estimating fungal propagule concentrations, species-specific calibration, suspension stability, wavelength selection, and independent validation remain important for routine applications. In this study, we developed an agar–water-assisted UV–visible spectrophotometric calibration protocol for estimating conidial concentration using B. bassiana as a model entomopathogenic fungus. A 0.1% (w/v) agar–water suspension was used in order to get homogeneous, stable dispersions of conidia for optical measurements. Calibration of conidia concentration was accomplished through reliable optical density (OD) values measured at wavelengths 500 nm, 530 nm, 560 nm, 600 nm, and 650 nm. Linear correlations were observed across the tested wavelengths, with the highest goodness of fit for the model at 650 nm (R² = 0.9907). The resulting regression equation, conidia concentration (×10⁷ mL⁻¹) = 4.184 × OD₆₅₀—0.12450, has been independently verified with separate conidia batches, resulting in acceptable relative errors ranging from 13.78% and 18.98%. This agar–water-assisted OD₆₅₀ calibration model provides a practical and species-specific tool for the standardization of conidial dosages in biopesticide research, facilitating the reliable evaluation and application of entomopathogenic fungi within integrated pest management systems.