As an aquatic environment pollutant, several studies have considered the negative impacts of antibiotics on marine primary producers (Sharma et al. 2021) (Miazek and Brozek-Pluska 2019). In the present study the effect of different groups of antibiotics on growth factors of T. chuii, including the cell density, dry weight, biomass productivity and chlorophyll contents were studied.
Quinoloes: In an earlier study 2.5 mg/L of CIP reduced the photosynthetic rate in S. capricornutum through 96 hours exposure, but significant difference was not observed in the chlorophyll contents, authors suggested the inhibitory effect of CIP may be due to the photosynthetic electron transport inhibition (Liu et al. 2011). In a later case Hagenbuch and Pinckney reported the marine species C. closterium and N. ramosissima sensitivity to CIP with IC50 values 55.43 and 72.12 mg/L respectively (Hagenbuch and Pinckney 2012). In contrary 2-150 mg/L dosages of CIP impact on C. pyrenoidosa were studied and microalgae growth was enhanced by 2-30 mg/L dosages whereas, it was declined by>100mg/L dosages and researchers proposed the high dosages of antibiotic may induce cells death, (Zhang et al. 2019).
On the other hand 16 days incubation of R. subcapitata with CIP, resulted in toxicant effect of 1-500µg/L dosages of the quinolone (Diniz et al. 2021).
Studding ENR effect on five fresh water green microalgae showed that low (≤1mg/L) dosages of ENR poorly inhibit the algal growth, whereas, the high dosages (≥100mg/L) of the quinolone, inhibit the algal growth strongly, 100 mg/L dosage of ENR showed inhibitory effect on different green fresh water microalgae species in a 11 days incubation (Xiong et al. 2017)a which is in contrary with the present study result, herein the enhancement effect of ENR on T. chuii was achieved.
Unlike some studies (Miazek and Brozek- Pluska, 2019) the enhanced growth of C. vulgaris was determined by adding NaCL to the algal medium containing LEV (Xiong et al. 2017)b. The same process was observed for applying salinity to Scenedesmus obliquus wastewater treatment (Xiong et al. 2017) b, The 76 hours EC50 value> 80 mg/L is reported for LEV incubating with P. subcapitata (Gonzalez-Pleiter et al. 2013) which is 85 times of the assessed EC50 of LEV for T. chuii in the present experiment and could explain the different sensitivity of fresh and marine species to the same antibiotics or the salinity role (Xiong et al. 2017) b on the quinolone influencing.
To knowledge of authors there is no evidence about NAL effect on microalgae growth. In the current experiment a weak inhibitory effect was observed by 1mg/L of Nal and LEV, the other dosages increased the T. Chuii growth.
In confirmation with quinolone stimulating effect on T.chuii and different effect of antibiotic dosages in present study, recently Ricky and colleague employed C. vulgaris for understanding if the green algae is suitable for CIP remediation in the high concentration; 5mg/L and in a 7 days incubation test (Richy et al. 2022) and reported reduction of algal growth up to the third date of the experiment, although the 7 days of exposure, resulted in stimulation the algal growth and the antibiotics removal by CIP 37% (Richy et al. 2022).
Tetracyclines: The toxic effect of tetracyclines on microalgae has been considered in different studies; TET inhibited the growth of fresh water green microalgae Selenastrum capricornutum and cyanobacterium Microcystis aeruginosa within the first 24 hour of a7 day incubation and affected the green algae more than the cyanobacter (Yang et al. 2013 )The antibiotic also inhibited the growth of C. vulgaris, Phaeodactylum tricornutum, Nodularia spumigena, and M. aeruginosa in longer exposing (10 days) (Siedlewicz et al. 2020) The 24 hours EC50 values 0.081 mg/ L was gained by incubation S. capricornutum with TET (Grinten et al. 2010)
In similar studies, OXY inhibited the growth of tetraselmis species, and IC50values 17.25 and 6.06 mg/L were obtained for T. suecica (Seoane et al. 2014) and T. chuii (Ferreira et al. 2007) respectively. It has become cleared that tetracyclines inhibit the chlorophyll synthesis and reduce the chlorophyll contents therefore (Liu et al. 2011). The reduction of algal growth is known due to chlorophyll synthesize decline and peroxide destruction of thylakoid membranes (Liu et al. 2011). Similar to the present study, the T. chuii specific growth rate and chlorophyll contents were inhibited by DOX and 96 hour EC50 22 mg/L was reported (Prata et al. 2018) which confirms the present study results, but herein the more toxicity of DOX is observed (EC50 =0.2754). Comparing data confirm the toxicity of tetracyclines on both fresh and marine species microalgae.
Macrolides: The results of present study suggest that inhibition effect of TYL is relates to the concentration of the macrolide, whereas 1mg/L of TYL increased the algal growth, the 0.5 and 0.25 mg/L reduced it. On the other hand the comparative experiment assessed the TYL effect on fresh and marine microalgae and evaluated IC50 0.27 and 0.99 mg/L for marine diatoms; Cylindrotheca closterium and Navicula ramosissima, respectively (Hagenbuch and Pinckney 2012 which are higher than evaluated parameters than fresh water species with 4days IC50 values; 74.3, 35 and 4.3 mg/L for C. vulgaris, D. subspicatus and R. subspicatus, whereas 1 day IC50 value 0.0089 mg/L was reported for P. subcapitata (Sharma et al. 2021) that seems the toxicant gets more effective over time.
Toxic effect of the other macrolide: ERY on green microalgae species have been evident previously by using S. capricornutum, C. vulgaris, Chlamydomonas reinhardtii and Ankestrodesmus falcatus, 0.35-12 mg/L of ERY inhibited 50% of the algal growth (Miazek and Brozek- Pluska 2019) the similar observation supports not only the toxicant effect of 0.3 mg/L ERY on S. capricornutum but also the reduction in the chlorophyll contents by increasing order of the macrolide concentration (Liu et al. 2011). More complete study demonstrated efficiency of ERY on transporting electron and photosystem I and II in cyanobacteria (Sharma et al. 2021) that explain the inhibitory mechanism of ERY on microalgae. The present study results are in line with the previous ones and confirm the inhibitory effect of ERY on T. chuii.
Penicillins: 76h EC507114.3 mg/L was evaluated by incubating P. subcapitata with AMP (Havelkova et al. 2016) that indicates the low toxicity of Penicilin to the eukaryote microalgae in line with other studies (Miazek and Brozek- Pluska 2019). Low sensitivity of green microalgae to AMX is reported (EC50>50 mg/L for Closterium ehrenbergii and R. subcapitata, and EC50>200 mg/L for C. pyrenoidosa) have been reported (Sharma et al. 2021). The present experiment obtained more sensitivity of T. chuii to penicillins than fresh water microalgae.
Sulfonamides: Several structure changes as mitochondria enlargement, lobed and displaced chloroplast, cell wall shrinkage was observed in incubation C. vulgaris with sulfonamides (Chen et al. 2020) Inhibition effect of TMP on fresh water green microalgae have been reported previously for different amount of sulfonamide and 3days IC50 value 90.83 mg/L and 4days IC50 values; >90.86 and >79mg/L were obtained for C. vulgaris and D. subspicatus and R. subspicatus respectively (Sharma et al. 2021) which are in accordant of present result, although T. chuii was inhibited by lower amounts of TMP in the current experiment and is more sensitive than fresh water species.
Comparing growth inhibitory effect of antibiotics has led to interesting result; Liu and colleagues indicated the more sensitivity of S. capricornutum to ERY than CIP (Liu et al. 2011). The more toxicity of protein synthesis inhibitor antibiotics than cell wall synthesis inhibitor antibiotics (TET>AMP) was proved earlier by Havelkova and team (Havelkova et al. 2016), a later comparative study revealed the lower toxicity of cell wall synthesis inhibitors on R. subcapitata among other antibiotics with different mode of action such as protein synthesis inhibitors and nucleic acid synthesis inhibitors; DOX>OXY>CIP>AMX (Fu et al. 2017),Which is in coordination with present study results, here the lower toxicity of AMX<DOX and OXY was revealed, the researchers proposed that antibiotics play as an electrophilic mechanism (Fu et al. 2017).
As Hagenbuch and Pinckney mentioned before and had determined earlier by Lai and team the IC50 values of fresh water microalgae to some antibiotics are higher than marine species, and marine microalgae are more sensitive to antibiotics than fresh water alga (Hagenbuch and Pinckney 2012). (Lai et al. 2009) which is similar to present experiment’s result for AMX, DOX, TET, OXY and explain the difference of obtained Ec50values in the current study and the other experiments.