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EFFECT OF CARBOXYLIC IONOPHOROUS ANTIBACTERIALS ON THE GROWTH OF SELECTED MICROALGAE
Citation:
Walker, C C., S. W. Heinzerling, AND J C. Kurtz. EFFECT OF CARBOXYLIC IONOPHOROUS ANTIBACTERIALS ON THE GROWTH OF SELECTED MICROALGAE.
Description:
Carboxylic ionophorous antibiotics are routinely used in cattle, chicken and turkey concentrated feedlot operations as anticoccidial and growth promotant feed additives and may, through runoff and effluents, enter adjacent waterways. The effects of these compounds on the growth of selected microalgae were evaluated in laboratory cultures using two dinoflagellates (Karenia brevis and Alexandrium monilatum), a raphidophyte (Chattonella subsalsa) and a diatom (Thalassiosira weissflogii). Cultures were grown in L1 media, cell density was determined periodically from 48-168h post-innoculum using fluorometry and microscopy, and 48-168h median inhibitory concentrations (IC-50s) were calculated. The three ionophores tested, monensin, lasalocid A and salinomycin, showed similar activity and were toxic at nanomolar concentrations for all microalgae tested. The activity was generally concentration and time dependent except for the effect of monensin on A. monilatum and T. weissflogii whose IC-50s remained relatively static from 48 to 168h. The 168h IC-50s of monensin for the dinoflagellates K. brevis and A. monilatum were 104 and 227 nM respectively. The 168h IC-50 for monensin and the diatom T. weissfloggii was 170 nM and the raphidophyte, C. subsalsa, was the most sensitive microalgae tested with a monensin 168h IC-50 of 4 nM (2.7 ng/mL). Lasalocid A and salinomycin exhibited activity against K. brevis at concentrations similar to those of monensin with 168H IC-50s of 42 and 66 nM, respectively. Such effects may alter phytoplankton community structure and adversely affect food web dynamics.