THE IMPORTANCE OF ALGAL-MICROBIAL INTERACTIONS ON CHEMICAL TOXICITY

Abstract

Microalgae in nature normally thrive in symbiotic relationships with a diverse community of microorganisms, primarily bacteria. Despite it is recognised the crucial role of species interactions on community ecotoxicology, there remains a significant gap in the comprehensive understanding of chemical toxicity on algae when exposed in monoculture or in more ecological settings, such as with consortia with bacteria. This study aimed to investigate the effects of biological complexity when assessing the toxicity of two chemical pollutants, the herbicide terbutryn and the antibiotic ciprofloxacin. The biological models used in this study were the green microalgae Chlorella vulgaris cultured alone or in consortia with a bacterium (i.e., Pseudomonas putida). Additionally, the study examined how the presence of glucose, a widely existed nutrient, in the growth medium modulates the toxicity of these chemicals. The research methodology involved growth inhibition ecotoxicological assays of the C. vulgaris in pure culture and in consortia with P. putida to terbutryn and ciprofloxacin in a concentrationresponse manner for 72 hours. Results revealed that C. vulgaris displayed heightened sensitivity to terbutryn when cultured in consortia with P. putida, indicating the significant influence of species interactions on toxicity when the biological model has the receptor of the toxicant. Competition was hypothesized as the main driver of observed increased chemical toxicity. Conversely, the presence of consortia of P. putida had a limited effect on the toxicity of ciprofloxacin, likely due to the stronger inhibitory effect of the antibiotic on bacteria, supporting the hypothesis that competition modulates chemical toxicity. Furthermore, this study also shows that the presence of glucose in the growth medium significantly influenced the toxicity of both terbutryn and ciprofloxacin, with higher EC50 values observed in glucose-supplemented media compared to standard media. These findings highlight the importance of considering biological complexity and nutrient conditions in ecotoxicological assessments, providing insights into the interplay between species interactions and chemical toxicity in aquatic ecosystems.