Interspecific competition between Microcystis aeruginosa and Chlamydomonas microsphaera stressed by tetracyclines

TL;DR: In this article , the effects of different concentrations of tetracyclines (tetracy-cline and oxytetracecline) in monoculture and co-culture were compared.

Abstract: The extensive use of tetracyclines in human and veterinary medicine causes contamination in the environment that could contribute to the spread of antibiotic-resistant bacteria or competition between species of phytoplankton. In this study, Microcystis aeruginosa (a bloom-forming cyanobacterium) and Chlamydomonas microsphaera (common green alga) were selected to test the effects of different concentrations of tetracyclines (tetracycline and oxytetracycline) in monoculture and co-culture. The results showed that compared with monoculture, the cell growth of C. microsphaera decreased significantly in co-culture treated with different concentrations of tetracycline and oxytetracycline. The ratios of inhibition of M. aeruginosa exposed to 0.1, 2, and 10 mg L-1 of tetracycline varied between 17.7 and 31.37% in co-culture compared with monoculture, while the cell growth of M. aeruginosa was enhanced by treatment with 0.1, 2, and 7.25 mg L-1 of oxytetracycline in co-culture. However, the cell growth of C. microsphaera was significantly inhibited by all the treatments in co-culture. With the treatment of tetracycline, the specific growth rate of M. aeruginosa was 0.36 to 0.31 day-1 in monoculture and co-culture, while that of C. microsphaera ranged from 0.38 to 0.26 day-1 in monoculture, and it decreased from 0.25 day-1 (0 mg L-1) to 0.08 day-1 (10 mg L-1) in co-culture. With the treatment of oxytetracycline, the specific growth rate of M. aeruginosa was stimulated in co-culture, while that of C. microsphaera was significantly inhibited in co-culture compared with monoculture. Therefore, although M. aeruginosa significantly inhibited C. microsphaera in co-culture with the tetracycline-free treatment, the competitive advantage of M. aeruginosa expanded following the addition of low or high concentrations of tetracyclines.