Toxicity of triclosan, penconazole and metalaxyl on Caulobacter crescentus and a freshwater microbial community as assessed by flow cytometry

摘要

Biocides are widely used for domestic hygiene, agri_cultural and industrial applications. Their widespread use has resulted in their introduction into the envi_ronment and raised concerns about potential delete_rious effects on aquatic ecosystems. In this study, the toxicity of the biocides triclosan, penconazole and metalaxyl were evaluated with the freshwater bacte_rium Caulobacter crescentus and with a freshwater microbial community using a combination of single-and double-stain flow cytometric assays. Growth of C. crescentus and the freshwater community were repressed by triclosan but not by penconazole or metalaxyl at concentrations up to 250 μM. The repres_sive effect of triclosan was dependent on culture con_ditions. Caulobacter crescentus was more sensitive to triclosan when grown with high glucose at high cell density than when grown directly in sterilized lake water at low cell density. This suggests that the use of conventional growth conditions may overestimate biocide toxicity. Additional experiments showed that the freshwater community was more sensitive to tri_closan than C. crescentus, with 10 nM of triclosan being sufficient to repress growth and change the phylogenetic composition of the community. These results demonstrate that isolate-based assays may underestimate biocide toxicity and highlight the importance of assessing toxicity directly on natural microbial communities. Because 10 nM of triclosan is within the range of concentrations observed in fresh_water systems, these results also raise concerns about the risk of introducing triclosan into the environment.