Toxic effect and adaptation in Scenedesmus intermedius to anthropogenic chloramphenicol contamination: genetic versus physiological mechanisms to rapid acquisition of xenobiotic resistance S. Sa ´nchez-Fortu ´n Æ F. Marva ´ Æ M. Rouco Æ E. Costas Æ V. Lo ´pez-Rodas Accepted: 21 February 2009 / Published online: 25 March 2009 Ó Springer Science+Business Media, LLC 2009 Abstract Anthropogenic water pollution is producing a challenge to the survival of phytoplankton populations. From an ecological point of view, the tolerance of these microorganisms to water pollution is of paramount importance since they are the principal primary producers of aquatic ecosystems. The adaptation of a common chlo- rophyta species (Scenedesmus intermedius) exposed to selected dose-response chloramphenicol (CAP) con- centrations has been analyzed. A fluctuation analysis demonstrated that CAP-resistant cells arise due to sponta- neous mutation which occurs randomly prior to the antibiotic exposure. CAP-inhibited growth and photosyn- thetic performance of algal cells at 0.28 mg/l, and the IC 50(72) value was established in 0.10 mg/l for both parameters. The mutation rate from CAP sensitivity to resistance was 1.01 9 10 -5 mutations per cell division, while the frequency of CAP-resistant allele in non-polluted environment was estimated to be 5.5 CAP-resistant mutants per 10 3 sensitive-cells. These results demonstrate that resistant mutants exhibit a diminished fitness until 5 mg/l of CAP, thus enabling the survival of microalgae population. Keywords Chloramphenicol  Scenedesmus intermedius  Toxicity  Mutation rate  Fluctuation analysis Introduction Human activities are changing biosphere-level processes (global change) and causing biodiversity crisis (Woodruff 2001; Myers and Knoll 2001). New substances are pol- luting water and causing environmental catastrophes in inland water systems. This is a problem of the utmost importance with basic research urgently needed to provide useful information to make future predictions, so that strategies may be designed to mitigate this environmental crisis (Ehrlich 2001). To this end, studies focused on dis- covering if essential microbes succumb to anthropogenic toxins are very significant (Woodruff 2001) since human activities are the greatest evolutionary force (Palumbi 2001). As microalgae are the primary producers of aquatic ecosystems (Kirk 1994; Falkowski and Raven 1997), the tolerance of these microorganisms to contaminated envi- ronments is very important from an ecological point of view. Antibiotics play a major role in modern agriculture and aquaculture activities with their use increasing in many developed nations (Sarmah et al. 2006). These drugs are mainly administered through medicated feed. This practice may result in the antibiotics entering the environment by leaching from uneaten feeds, unabsorbed particles present in manure, or from the discharge of aquatic animals (Robinson et al. 2007). Studies performed in intensive fish farms have demonstrated that about 70–80% of applied antibiotics administered to fish as food additives end up in the aquatic environment. This may result in adverse eco- logical effects, including the development of resistant bacterial populations, direct toxicity to microbiota, and/or possible risks in the transfer of these antibiotic resistances to human pathogenic microbes (Rigos et al. 2004). Therefore, the overuse and misuse of certain antibiotics has S. Sa ´nchez-Fortu ´n (&) Department of Toxicology and Pharmacology, Complutense University, Avda. Puerta de Hierro, s/n, 28040 Madrid, Spain e-mail: fortun@vet.ucm.es F. Marva ´  M. Rouco  E. Costas  V. Lo ´pez-Rodas Department of Genetics, School of Veterinary Sciences, Complutense University, Avda. Puerta de Hierro, s/n, 28040 Madrid, Spain 123 Ecotoxicology (2009) 18:481–487 DOI 10.1007/s10646-009-0303-8