Cultivation of Anabaena sp. at Different Phosphorus Excess Concentrations: Growth Parameters, Value-Added Metabolites, and Microcystin-LR Production

Abstract

Phosphorus is a key driver of cyanobacterial proliferation and the production of secondary metabolites in freshwater ecosystems. In this study, the effects of different phosphorus concentrations, including 7.10 (control treatment), 7.74, 8.38, and 9.66 mg L^-1 (CP₂₃₀, TP₂₅₀, TP₂₇₁, and TP₃₁₂, respectively), on growth, valuable biochemicals, as well as the toxicity potential of Anabaena sp. in BG-11 medium were investigated. Elevated phosphorus levels significantly enhanced chlorophyll a and total carotenoid contents, with the highest values recorded under 8.38 mg P L^-1 (1.16 ± 0.04 mg L^-1 and 1.07 ± 0.30 mg L^-1, respectively). This treatment also yielded the greatest total phenolic content (8.04 ± 0.32 mg GAE g^-1 DW^-1) and antioxidant activity (IC₅₀ = 2.98 ± 0.02 mg mL^-1). Antibacterial assays demonstrated notable inhibition zones against Escherichia coli (9.30 ± 1.20 mm) and Staphylococcus aureus (4.50 ± 0.90 mm) in the treatment with 8.38 mg P L^-1. GC/MS analysis showed that the cyanobacterial extracts contained several biomolecules such as phenol, 2,4-Di-tert-butylphenol, hexadecanoic acid methyl ester, and other compounds with antioxidant and antibacterial activity. Palmitic acid, palmitoleic acid, oleic acid, and linoleic acid were the dominant fatty acids in the lipid profile of Anabaena sp. In addition to its antibacterial properties, Anabaena sp. showed moderate to low toxicity against Daphnia magna, depending on the phosphorus concentration of the treatments. The findings of the current research indicated that Anabaena sp. not only produces cyanotoxins but also beneficial chemicals, positioning it as a potential new target for antibacterial and antioxidant drug development.

Keywords: Daphnia magna; antioxidant; cyanotoxins; fatty acids; phosphorus.

FIGURE 1

A schematic flow diagram summarizing the experimental design of the present study.

FIGURE 2

The effect of different concentrations of phosphorus on dry biomass (a) and pigments production (b) of Anabaena sp. Data are means ± SD from three replicates. Bars with different letters indicate significant differences according to Duncan's test (p < 0.05).

FIGURE 3

Effect of different concentrations of phosphorus on total phenolic content of Anabaena sp. Data represent means ± SD from three replicates. Bars with different letters indicate significant differences according to Duncan's test (p < 0.05).

FIGURE 4

Amounts of major components identified in methanolic extract of Anabaena sp. in different experimental treatments (a‐d). The category named ‘Others’ includes: Gibberellic acid, propanoate, neophytadiene, N‐ethyl‐1,3‐dithioisoindoline, 1,3‐Bis(trimethyl)benzene, and 3‐Nitrophthalic acid.

FIGURE 5

Effect of different methanolic extracts and media initial P concentrations on the antioxidant activity of Anabaena sp. Data represent means ± SD from three replicates. Bars with different letters indicate significant differences according to Duncan's test (p < 0.05).

FIGURE 6

Effect of lyophilized biomass of Anabaena sp. grown in different phosphorus concentrations on survival of D. magna during 96 h of exposure. Data present means ± SD from three replicates. Bars with different letters indicate significant differences according to Duncan's test (p < 0.05).