Abstract
Many pharmaceuticals have negative effects on biota when released into the environment. For example, recent work has shown that the commonly prescribed antidiabetic drug, metformin (N,N-dimethylbiguanide), has endocrine disrupting effects on fish. However, effects of metformin on aquatic primary producers are poorly known. We exposed cultured isolates of a freshwater chlorophyte, Chlorella vulgaris, to a range of metformin concentrations (0–767.9 mg L-1) to test the hypothesis that exposure negatively affects photosynthesis and growth. A cessation of growth, increase in non-photochemical quenching (NPQ, NPQmax), and reduced electron transport rate (ETR) were observed 24 h after exposure to a metformin concentration of 767.8 mg L-1 (4.6 mM). By 48 h, photosynthetic efficiency of photosystem II (Fv/Fm), α, the initial slope of the ETR-irradiance curve, and Ek (minimum irradiance required to saturate photosynthesis) were reduced. At a lower concentration (76.8 mg L-1), negative effects on photosynthesis (increase in NPQ, decrease in ETR) were delayed, occurring between 72 and 96 h. No negative effects on photosynthesis were observed at an exposure concentration of 1.5 mg L-1. It is likely that metformin impairs photosynthesis either through downstream effects from inhibition of complex I of the electron transport chain or via activation of the enzyme, SnRK1 (sucrose non-fermenting-related kinase 1), which acts as a cellular energy regulator in plants and algae and is an ortholog of the mammalian target of metformin, AMPK (5' adenosine monophosphate-activated protein kinase).
Highlights
Pharmaceuticals and personal care products (PPCPs) comprise a diverse class of chemical compounds that have gained attention as chemicals of emerging concern (CECs) due to their widespread detection in aquatic environments [1,2,3] and because of their bioactive properties [4,5,6]
Metformin reduced the culture density of C. vulgaris at exposures of 76.8 mg L-1 (0.46 mM) and 767.8 mg L-1 (4.6 mM) due to a rapid reduction in growth that was not observed in controls (Fig 1)
(NPQ), the dissipation of light energy not used to carry out photochemistry
Summary
Pharmaceuticals and personal care products (PPCPs) comprise a diverse class of chemical compounds that have gained attention as chemicals of emerging concern (CECs) due to their widespread detection in aquatic environments [1,2,3] and because of their bioactive properties [4,5,6]. The ecological effects of many active pharmaceutical ingredients (APIs) are poorly known, several have been implicated in acute [7,8] and chronic toxicity [9,10,11] to biota. Direct toxic effects of APIs on microalgae have been observed, with effects varying according to the species and drug [12,13,14,15,16]. Metformin and algal photosynthesis do not necessarily reflect the views of these funders. The work was supported through a Robert Malouf Marine Studies Fellowship to BMC. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript
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