Toxic Effects Of Polyhexamethylene Biguanide(PHMB) On Chlorella Pyrenoidosa

Polyhexamethylene biguanide(PHMB),a novel eco-friendly surfactant with wide spectrum,high efficiency,and long validity period,boasts strong bactericidal and bacteriostatic properties.PHMB is easily storable and transportable and insensitive to temperature and light with weak toxic and irritating effects.This surfactant finds widespread use in the pharmaceutical,daily chemical,and aquaculture industries.However,the persistent environmental pollution caused by surfactants still poses a significant threat to aquatic flora and fauna.As primary producers,algae play a crucial role in maintaining the balance of aquatic ecosystems.Chlorella pyrenoidosa is one of the common green algae,and is also a natural food commonly used in aquatic animals,with small individuals,easy to cultivate,fast growth,short reproductive cycle,more sensitive to stress,etc.,and is often selected as a model organism in toxicology experiments.In order to understand the influence of PHMB on aquatic ecological environment,the toxic effect of different concentrations of PHMB on C.pyrenoidosa was studied,so as to provide a theoretical basis for the application of PHMB in aquaculture.In this study,different concentrations of PHMB used to C.pyrenoidosa a after 0,3,6,and 9 d stress,the effects on the growth and photosynthetic physiological factors of C.pyrenoidosa were studied,and the changes of cell surface and ultrastructure of C.pyrenoidosa,as well as the changes of oxidative stress and photosynthesis-related gene expression of C.pyrenoidosa.The main research results were as follows:1.The cell density of Chlorella pyrenoidosa decreased with the increase of PHMB concentration,and the growth inhibition of Chlorella pyrenoidosa by PHMB manifested as a time-concentration effect.The change trend of chlorophyll a(Chl a)and chlorophyll b(Chl b)contents in Chlorella pyrenoidosa was positively correlated with the growth curve,and the contents in the concentration group(2 mg/L)and the high concentration group(4 mg/L)decreased significantly in the 6th and 9th days.At the same time,under PHMB stress,the content of soluble protein and soluble sugar in Chlorella pyrenoidosa decreased significantly,with the most significant change in the high concentration group(4 mg/L).At the same time,under PHMB stress,the content of soluble protein and soluble sugar in Chlorella pyrenoidosa decreased significantly,with the most significant change in the high concentration group(4 mg/L).2.The ionic conductivity of protein nuclei increases with the increase of PHMB concentration within 3-9 days.On the third day of exposure,no group aggregation phenomenon was found in all treatment groups.On the 6th day of exposure,group aggregation occurred in all experimental groups with different concentrations,and with the increase of concentration,the group aggregation phenomenon became more obvious.On the 9th day of exposure,in different concentration groups,algal cells showed a population aggregation phenomenon,which was more pronounced than on the 6th day,with more clustered substances.In the observation of ultrastructure,it was found that PHMB caused varying degrees of damage to the external structure of algae cells,including cell wall cracking and content leakage.The internal structure has obvious malformations,such as the loss of cell matrix,the destruction of the integrity of chloroplast and thylakoid,the deformation of mitochondria,the reduction of mitochondrial cristae,the atrophy of pigment bodies and lysosomes,the destruction of protein nuclear structure,and the disappearance of vacuoles.3.The activities of antioxidant enzymes(CAT,SOD,GSH-Px)and the content of MDA of C.pyrenoidosa under PHMB exposure at different time periods were determined.The results showed that PHMB of different concentrations induced the antioxidant stress response of Chlorella pyrenoidosa within 3-9 days.In the determination of the relative expression of photosynthesis-related genes pbsA,rbcL and rbcS,it showed a strong induction effect in C.pyrenoidosa after 3 days of PHMB exposure.After 9 days,the activities of antioxidant enzymes decreased significantly in the medium and high concentration groups(2 mg/L,4 mg/L).The expression changes of the rbcS gene were different from those of psbA and rbcL.After 9 days of exposure,the expression level in the high concentration group(4 mg/L)was significantly upregulated.This study showed the possible toxic effects of PHMB on aquatic animals and plants and its mechanism,which provided a theoretical basis for the rational use of PHMB in production.