Effects of single and combined pollution of antibiotics and cadmium on growth of Synechocystis sp.PCC6803
Antibiotics and heavy metals are persistent pollutants in the environment,and the assess-ment of their toxicity to organisms has always been a hotspot of study.This article investigated the effects of single and combined pollution of tetracycline/sulfamethoxazole and cadmium ions on the growth of Syn-echocystis sp.PCC6803.The results showed that a single exposure to 100 ng/L sulfamethoxazole(SMX)stimulated the growth and photosynthetic activity of Synechocystis,whereas treatment with tetracycline(TC)had no significant effect.Cadmium ions(Cd2+)at 0.001 mg/L did not significantly affect the physiol-ogy of Synechocystis,but Cd2+at 0.5 mg/L significantly inhibited the growth and photosynthesis of Syn-echocystis.This concentration downregulated photosynthesis-related gene(psbA2),disrupted the antioxi-dant system of Synechocystis,damaged its cell membranes,and stimulated the secretion of its extracellular polysaccharides.When 100 ng/L TC coexisted with 0.001 mg/L Cd2+synergistically,the cellular esterase activity was stimulated.100 ng/L SMX alleviated oxidative damage caused by 0.5 mg/L Cd2+,resulting in the reduced production of reactive oxygen species(ROS),the decreased activity of superoxide dismutase(SOD),and the low content of malonaldehyde(MDA)compared to the group treated by single 0.5 mg/L Cd2+.When both were present simultaneously,they synergistically stimulated the activity of esterase in Synechocystis.Low concentrations of tetracycline had minimal impact on cell growth and did not significant-ly alter the cytotoxicity of Cd2+on cells.In contrast,low concentrations of sulfamethoxazole promoted cell growth and mitigated the cytotoxic effects of Cd2+on cells.It is indicated that it is necessary to comprehen-sively consider the combined pollution of antibiotics and heavy metals when pollution is assessed.
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