Freshwater cyanobacteria and antibiotic pollution: The Ecotoxicological and Antibiotic Resistance perspectives

The release of antibiotics in natural ecosystems led to the development of antibiotic resistant (AR) microorganisms and alters the diversity/functioning of natural microbial communities. Freshwater cyanobacteria (CB) have been considered sensitive to antibiotics and they have been used as biologic indicators in environmental risk assessment of water contaminants, such as antibiotics. However, we have shown that CB strains from water environments exhibits reduced susceptibility to some antibiotics (nalidixic acid, trimethoprim), irrespective of the tested specie (Microcystis aeruginosa, Aphanizomenon gracile; Anabaena berghii, Planktothrix agardhii, Planktothrix mougeotti). The failure to detect genes conferring resistance to these antibiotics by PCR does not exclude the possibility of CB harbor AR determinants. NGS sequencing will help us to understand if unknown AR genes are present in CB genomes. Besides, we may also hypothesize that CB are intrinsically resistant to those compounds. On the other hand, the susceptibility to other antibiotics depended of the specie and/or the specie origin (freshwater reservoirs, wastewater treatment plants). Moreover, we also detect genes associated with resistance to other antibiotics (streptomycin, sulfonamides) and a class-1-type integron, in some strains. This suggests that CB might acquire resistant determinants from AR microbiota sharing the same habitats. Thus, the impact of antibiotic pollution in natural occurring CB is far from being elucidated. CB seems to have a role on water resistome but CB communities and their important ecological roles (primary and O2 production, CO2 fixation) may be also hampered by antibiotic exposure.N/