Isolation, identification and effect of heavy metals on the growth of Cylindrospermopsis raciborskii helix from shrimp ponds

Abstract:

[Objective] We examined the physiological characteristics of invasive cyanobacterium Cylindrospermopsis raciborskii helix isolated from Litopenaeus vannamei culture ponds. [Methods] The algal strain was isolated and purified from shrimp ponds in Chenghai, Shantou, and identified by morphology and 16S rRNA sequence analysis. Then, with the general culture media of CT and BG11, we optimized the culture conditions. Finally, we analyzed the effect of heavy metals Cu²⁺ (0-0.8 mg/L), Cd²⁺ (0-4 mg/L) and Pb²⁺ (0-80 mg/L) on the growth of the isolated strain. [Results] The identity of 16S rRNA sequence of the isolated strain was higher than 98% with that of typical strains of Cylindrospermopsis raciborskii from GenBank. Under laboratory culture conditions, the optimal culture medium for the growth of the isolated strain was the modified BG11 (N 62 mg/L, N:P=9:1), the exponential biomass and growth rate were up to (0.632±0.170)×10⁷/L, (0.063±0.001)/d, respectively. The isolated strain tolerated heavy metals Cu²⁺, Cd²⁺ and Pb²⁺, and the tolerance concentrations was Pb²⁺ 1-40 mg/L, Cd²⁺ 0-0.5 mg/L, Cu²⁺ 0-0.2 mg/L. Furthermore, Cu²⁺ and Cd²⁺ inhibited the growth of the isolated strain, and the inhibition increased with enhancing of heavy metal concentration and contact time, the 96 h EC₅₀ of Cu²⁺ and Cd²⁺ were 0.125 and 0.551 mg/L for the strain, respectively, but Pb²⁺(0-80 mg/L) had a dual effect on its growth, which promoted growth at low concentration (≤ 40 mg/L) and inhibited growth at high concentration (≥ 80 mg/L). [Conclusion] A strain of Cylindrospermopsis raciborskii isolated from L. vannamei culture ponds has the potential of adsorbing heavy metal ions in shrimp ponds.