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In this study, the acute toxicity effects of a fluorescent xanthene dye, Rhodamine B (RhB), widely used in textile, paper, and leather industries was investigated on a freshwater microalgae Chlorella vulgaris. The acute toxicity of RhB on C. vulgaris was determined by examining the growth, cell morphology, pigment production, protein content, and the activities of oxidative stress enzymes. Based on the results of the toxicity study of 24–96 h, the median inhibitory concentration (IC50) values ranged from 69.94 to 31.29 mg L−1. The growth of C. vulgaris was conspicuously inhibited by RhB exposure, and the cell surfaces appeared to be seriously shrunk in SEM analysis. The growth of C. vulgaris was hindered after exposure to graded concentrations (10–50 mg L−1) of RhB. A significant reduction in growth rate, pigment synthesis (chlorophyll a, chlorophyll b, and carotenoid), and protein content was recorded in a dose-dependent manner. After 96 h exposure of C. vulgaris to 50 mg L−1 RhB, chlorophyll a, chlorophyll b, carotenoids, and protein contents were reduced by 71.59, 74.90, 65.84, and 74.20%, respectively. The activities of the antioxidant enzymes peroxidase (POD), and catalase (CAT) also increased markedly in the presence of RhB. A notable effect was observed on oxidative enzymes catalase and peroxidase, indicating that oxidative stress may be the primary factor in the inhibition of growth and pigment synthesis. Consequently, the experimental acute toxicity data were compared to the QSAR prediction made by the ECOSAR programme. Results showed that the experimental acute toxicity values were 67.74-fold lower than the ECOSAR predicted values. The study provides convincing evidence for the metabolic disruption in the ubiquitous microalgae C. vulgaris due to the RhB dye toxicity. [ABSTRACT FROM AUTHOR]

The present study reports the production, extraction, partial characterization, biological activities and use in textile dyeing of an orange pigment from Metabacillus idriensis strain LipT27 (MN818522.2). Pigment production occurred with 400 µg carotenoid/g biomass yield. Characterization of the methanol extracts of pigment by UV–Visible spectrophotometry, TLC, NMR, and FTIR indicated that the pigment was a carotenoid group pigment. The pigment exhibited antibacterial activity against Yersinia enterocolitica, Staphylococcus aureus, and Escherichia coli and antioxidant potential in DPPH and ABTS assays. In addition, the crude pigment was used in dyeing cotton fabrics. The first carotenoid from M. idriensis, which has strong antibacterial and antioxidant properties and also has the potential to be used as a dyeing agent for textiles, suggests that it can be used as a natural colorant substitute to synthetic dyes. [ABSTRACT FROM AUTHOR]